From f00da4579e2b00c3cb1577fc6fe78aca5b87423e Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Thu, 11 Feb 2021 18:56:15 +0000
Subject: [PATCH 01/22] add get dims, coords, indexes

---
 cf_xarray/accessor.py | 96 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 72 insertions(+), 24 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 01c2ce4d..ced60af4 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -249,7 +249,9 @@ def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List
         return []
 
 
-def _get_axis_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
+def _get_axis_coord(
+    var: Union[DataArray, Dataset], key: str, error: bool = True
+) -> List[str]:
     """
     Translate from axis or coord name to variable name
 
@@ -283,7 +285,7 @@ def _get_axis_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
     """
 
     valid_keys = _COORD_NAMES + _AXIS_NAMES
-    if key not in valid_keys:
+    if error and key not in valid_keys:
         raise KeyError(
             f"cf_xarray did not understand key {key!r}. Expected one of {valid_keys!r}"
         )
@@ -313,6 +315,56 @@ def _get_axis_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
     return list(results)
 
 
+def _get_all(var: Union[DataArray, Dataset], key: str) -> List[str]:
+
+    results = set(_get_axis_coord(var, key, error=False))
+    for func in (_get_measure, _get_with_standard_name):
+        results.update(func(var, key))
+
+    return list(results)
+
+
+def _get_dims(var: Union[DataArray, Dataset], key: str) -> List[str]:
+    results = set(_get_all(var, key)).intersection(var.dims)
+    return list(results)
+
+
+def _get_single_dim(var: Union[DataArray, Dataset], key: str) -> List[str]:
+    return _get_single(var, key, _get_dims)
+
+
+def _get_coords(var: Union[DataArray, Dataset], key: str) -> List[str]:
+    results = set(_get_all(var, key)).intersection(var.coords)
+    return list(results)
+
+
+def _get_single_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
+    return _get_single(var, key, _get_coords)
+
+
+def _get_indexes(var: Union[DataArray, Dataset], key: str) -> List[str]:
+    results = set(_get_all(var, key)).intersection(var.indexes)
+    return list(results)
+
+
+def _get_single_index(var: Union[DataArray, Dataset], key: str) -> List[str]:
+    return _get_single(var, key, _get_indexes)
+
+
+def _get_single(var: Union[DataArray, Dataset], key: str, func):
+
+    results = func(var, key)
+
+    if len(results) > 1:
+        raise KeyError(
+            f"Multiple results for {key!r} found: {results!r}. I expected only one."
+        )
+    elif len(results) == 0:
+        raise KeyError(f"No results found for {key!r}.")
+
+    return results
+
+
 def _get_measure_variable(
     da: DataArray, key: str, error: bool = True, default: str = None
 ) -> List[DataArray]:
@@ -374,34 +426,30 @@ def _get_with_standard_name(
 
 #: Default mappers for common keys.
 _DEFAULT_KEY_MAPPERS: Mapping[str, Tuple[Mapper, ...]] = {
-    "dim": (_get_axis_coord, _get_with_standard_name),
-    "dims": (_get_axis_coord, _get_with_standard_name),  # transpose
-    "drop_dims": (_get_axis_coord, _get_with_standard_name),  # drop_dims
-    "dimensions": (_get_axis_coord, _get_with_standard_name),  # stack
-    "dims_dict": (_get_axis_coord, _get_with_standard_name),  # swap_dims, rename_dims
-    "shifts": (_get_axis_coord, _get_with_standard_name),  # shift, roll
-    "pad_width": (_get_axis_coord, _get_with_standard_name),  # shift, roll
-    "names": (
-        _get_axis_coord,
-        _get_measure,
-        _get_with_standard_name,
-    ),  # set_coords, reset_coords, drop_vars
-    "labels": (_get_axis_coord, _get_measure, _get_with_standard_name),  # drop
-    "coords": (_get_axis_coord, _get_with_standard_name),  # interp
-    "indexers": (_get_axis_coord, _get_with_standard_name),  # sel, isel, reindex
+    "dim": (_get_dims,),
+    "dims": (_get_dims,),  # transpose
+    "drop_dims": (_get_dims,),  # drop_dims
+    "dimensions": (_get_dims,),  # stack
+    "dims_dict": (_get_dims,),  # swap_dims, rename_dims
+    "shifts": (_get_dims,),  # shift, roll
+    "pad_width": (_get_dims,),  # shift, roll
+    "names": (_get_all,),  # set_coords, reset_coords, drop_vars
+    "labels": (_get_all,),  # drop
+    "coords": (_get_coords,),  # interp
+    "indexers": (_get_indexes,),  # sel, isel, reindex
     # "indexes": (_get_axis_coord,),  # set_index
-    "dims_or_levels": (_get_axis_coord, _get_with_standard_name),  # reset_index
-    "window": (_get_axis_coord, _get_with_standard_name),  # rolling_exp
-    "coord": (_get_axis_coord_single,),  # differentiate, integrate
+    "dims_or_levels": (_get_indexes,),  # reset_index
+    "window": (_get_dims,),  # rolling_exp
+    "coord": (_get_coords,),  # differentiate, integrate
     "group": (
         _get_axis_coord_single,
         _get_groupby_time_accessor,
         _get_with_standard_name,
     ),
-    "indexer": (_get_axis_coord_single,),  # resample
-    "variables": (_get_axis_coord, _get_with_standard_name),  # sortby
+    "indexer": (_get_single_index,),  # resample
+    "variables": (_get_all,),  # sortby
     "weights": (_get_measure_variable,),  # type: ignore
-    "chunks": (_get_axis_coord, _get_with_standard_name),  # chunk
+    "chunks": (_get_dims,),  # chunk
 }
 
 
@@ -907,7 +955,7 @@ def _rewrite_values(
         # these are valid for .sel, .isel, .coarsen
         all_mappers = ChainMap(
             key_mappers,
-            dict.fromkeys(var_kws, (_get_axis_coord, _get_with_standard_name)),
+            dict.fromkeys(var_kws, (_get_all,)),
         )
 
         for key in set(all_mappers) & set(kwargs):

From 365b7e800ed930b0c6993d48f37a409821bf0fb5 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Thu, 11 Feb 2021 12:21:17 -0700
Subject: [PATCH 02/22]  better mappers draft

---
 cf_xarray/accessor.py            | 73 +++++++++++++++++++++-----------
 cf_xarray/tests/test_accessor.py |  3 +-
 doc/whats-new.rst                |  2 +-
 3 files changed, 50 insertions(+), 28 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 01c2ce4d..6accdc56 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -372,36 +372,46 @@ def _get_with_standard_name(
     return varnames
 
 
+def _get_all(obj: Union[DataArray, Dataset], key: Union[str, List[str]]) -> List[str]:
+    all_mappers = (_get_axis_coord, _get_measure, _get_with_standard_name, _get_measure)
+    results = apply_mapper(all_mappers, obj, key, error=False, default=None)
+    return results
+
+
+def _get_dims(obj: Union[DataArray, Dataset], key: Union[str, List[str]]):
+    return [k for k in _get_all(obj, key) if k in obj.dims]
+
+
+def _get_indexes(obj: Union[DataArray, Dataset], key: Union[str, List[str]]):
+    return [k for k in _get_all(obj, key) if k in obj.indexes]
+
+
+def _get_coords(obj: Union[DataArray, Dataset], key: Union[str, List[str]]):
+    return [k for k in _get_all(obj, key) if k in obj.coords]
+
+
 #: Default mappers for common keys.
 _DEFAULT_KEY_MAPPERS: Mapping[str, Tuple[Mapper, ...]] = {
-    "dim": (_get_axis_coord, _get_with_standard_name),
-    "dims": (_get_axis_coord, _get_with_standard_name),  # transpose
-    "drop_dims": (_get_axis_coord, _get_with_standard_name),  # drop_dims
-    "dimensions": (_get_axis_coord, _get_with_standard_name),  # stack
-    "dims_dict": (_get_axis_coord, _get_with_standard_name),  # swap_dims, rename_dims
-    "shifts": (_get_axis_coord, _get_with_standard_name),  # shift, roll
-    "pad_width": (_get_axis_coord, _get_with_standard_name),  # shift, roll
-    "names": (
-        _get_axis_coord,
-        _get_measure,
-        _get_with_standard_name,
-    ),  # set_coords, reset_coords, drop_vars
-    "labels": (_get_axis_coord, _get_measure, _get_with_standard_name),  # drop
-    "coords": (_get_axis_coord, _get_with_standard_name),  # interp
-    "indexers": (_get_axis_coord, _get_with_standard_name),  # sel, isel, reindex
+    "dim": (_get_dims,),  # (_get_axis_coord, _get_with_standard_name),
+    "dims": (_get_dims,),  # (_get_axis_coord, _get_with_standard_name),  # transpose
+    "drop_dims": (_get_dims,),  # drop_dims
+    "dimensions": (_get_dims,),  # stack
+    "dims_dict": (_get_dims,),  # swap_dims, rename_dims
+    "shifts": (_get_dims,),  # shift, roll
+    "pad_width": (_get_dims,),  # shift, roll
+    "names": (_get_all,),  # set_coords, reset_coords, drop_vars
+    "labels": (_get_indexes,),  # drop_sel
+    "coords": (_get_dims,),  # interp
+    "indexers": (_get_indexes,),  # sel, isel, reindex
     # "indexes": (_get_axis_coord,),  # set_index
-    "dims_or_levels": (_get_axis_coord, _get_with_standard_name),  # reset_index
-    "window": (_get_axis_coord, _get_with_standard_name),  # rolling_exp
+    "dims_or_levels": (_get_dims,),  # reset_index
+    "window": (_get_dims,),  # rolling_exp
     "coord": (_get_axis_coord_single,),  # differentiate, integrate
-    "group": (
-        _get_axis_coord_single,
-        _get_groupby_time_accessor,
-        _get_with_standard_name,
-    ),
-    "indexer": (_get_axis_coord_single,),  # resample
-    "variables": (_get_axis_coord, _get_with_standard_name),  # sortby
+    "group": (_get_all, _get_groupby_time_accessor),  # groupby
+    "indexer": (_get_indexes,),  # resample
+    "variables": (_get_all,),  # sortby
     "weights": (_get_measure_variable,),  # type: ignore
-    "chunks": (_get_axis_coord, _get_with_standard_name),  # chunk
+    "chunks": (_get_dims,),  # chunk
 }
 
 
@@ -430,6 +440,9 @@ def _build_docstring(func):
     can be used for arguments.
     """
 
+    get_all_docstring = (
+        f"One or more of {(_AXIS_NAMES + _COORD_NAMES)!r};\n\t\t\tor standard names"
+    )
     # this list will need to be updated any time a new mapper is added
     mapper_docstrings = {
         _get_axis_coord: f"One or more of {(_AXIS_NAMES + _COORD_NAMES)!r}",
@@ -437,6 +450,10 @@ def _build_docstring(func):
         _get_groupby_time_accessor: "Time variable accessor e.g. 'T.month'",
         _get_with_standard_name: "Standard names",
         _get_measure_variable: f"One of {_CELL_MEASURES!r}",
+        _get_all: get_all_docstring,
+        _get_indexes: get_all_docstring + "present in .indexes",
+        _get_dims: get_all_docstring + "present in .dims",
+        _get_coords: get_all_docstring + "present in .coords",
     }
 
     sig = inspect.signature(func)
@@ -1374,6 +1391,12 @@ def guess_coord_axis(self, verbose: bool = False) -> Union[DataArray, Dataset]:
                     obj[var].attrs = dict(ChainMap(obj[var].attrs, ATTRS[axis]))
         return obj
 
+    def drop(self, *args, **kwargs):
+        raise NotImplementedError(
+            "cf-xarray does not support .drop."
+            "Please use .cf.drop_vars or .cf.drop_sel as appropriate."
+        )
+
 
 @xr.register_dataset_accessor("cf")
 class CFDatasetAccessor(CFAccessor):
diff --git a/cf_xarray/tests/test_accessor.py b/cf_xarray/tests/test_accessor.py
index 2682ccf9..af8e5570 100644
--- a/cf_xarray/tests/test_accessor.py
+++ b/cf_xarray/tests/test_accessor.py
@@ -849,8 +849,7 @@ def test_standard_name_mapper():
 
 
 @pytest.mark.parametrize("obj", objects)
-@pytest.mark.parametrize("attr", ["drop", "drop_vars", "set_coords"])
-@pytest.mark.filterwarnings("ignore:dropping .* using `drop` .* deprecated")
+@pytest.mark.parametrize("attr", ["drop_vars", "set_coords"])
 def test_drop_vars_and_set_coords(obj, attr):
 
     # DataArray object has no attribute set_coords
diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index e6be6541..787d51fb 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -9,7 +9,7 @@ v0.4.1 (unreleased)
 - Replace ``cf.describe()`` with :py:meth:`Dataset.cf.__repr__`. By `Mattia Almansi`_.
 - Automatically set ``x`` or ``y`` for :py:attr:`DataArray.cf.plot`. By `Deepak Cherian`_.
 - Added scripts to document :ref:`criteria` with tables. By `Mattia Almansi`_.
-- Support for ``.drop()``, ``.drop_vars()``, ``.drop_sel()``, ``.drop_dims()``, ``.set_coords()``, ``.reset_coords()``. By `Mattia Almansi`_.
+- Support for ``.drop_vars()``, ``.drop_sel()``, ``.drop_dims()``, ``.set_coords()``, ``.reset_coords()``. By `Mattia Almansi`_.
 - Support for using ``standard_name`` in more functions. (:pr:`128`) By `Deepak Cherian`_
 - Allow :py:meth:`DataArray.cf.__getitem__` with standard names. By `Deepak Cherian`_
 - Rewrite the ``values`` of :py:attr:`Dataset.coords` and :py:attr:`Dataset.data_vars` with objects returned

From 6f0b2d4c65985f7f0eb8b6bd87bed273ac4fbc52 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Thu, 11 Feb 2021 21:27:20 +0000
Subject: [PATCH 03/22] remove malmans2 _get_funcs

---
 cf_xarray/accessor.py | 50 ++++++-------------------------------------
 1 file changed, 7 insertions(+), 43 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index e0416dec..f9eaf6db 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -315,42 +315,6 @@ def _get_axis_coord(
     return list(results)
 
 
-def _get_all(var: Union[DataArray, Dataset], key: str) -> List[str]:
-
-    results = set(_get_axis_coord(var, key, error=False))
-    for func in (_get_measure, _get_with_standard_name):
-        results.update(func(var, key))
-
-    return list(results)
-
-
-def _get_dims(var: Union[DataArray, Dataset], key: str) -> List[str]:
-    results = set(_get_all(var, key)).intersection(var.dims)
-    return list(results)
-
-
-def _get_single_dim(var: Union[DataArray, Dataset], key: str) -> List[str]:
-    return _get_single(var, key, _get_dims)
-
-
-def _get_coords(var: Union[DataArray, Dataset], key: str) -> List[str]:
-    results = set(_get_all(var, key)).intersection(var.coords)
-    return list(results)
-
-
-def _get_single_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
-    return _get_single(var, key, _get_coords)
-
-
-def _get_indexes(var: Union[DataArray, Dataset], key: str) -> List[str]:
-    results = set(_get_all(var, key)).intersection(var.indexes)
-    return list(results)
-
-
-def _get_single_index(var: Union[DataArray, Dataset], key: str) -> List[str]:
-    return _get_single(var, key, _get_indexes)
-
-
 def _get_single(var: Union[DataArray, Dataset], key: str, func):
 
     results = func(var, key)
@@ -424,28 +388,28 @@ def _get_with_standard_name(
     return varnames
 
 
-def _get_all(obj: Union[DataArray, Dataset], key: Union[str, List[str]]) -> List[str]:
-    all_mappers = (_get_axis_coord, _get_measure, _get_with_standard_name, _get_measure)
+def _get_all(obj: Union[DataArray, Dataset], key: str) -> List[str]:
+    all_mappers = (_get_axis_coord, _get_measure, _get_with_standard_name)
     results = apply_mapper(all_mappers, obj, key, error=False, default=None)
     return results
 
 
-def _get_dims(obj: Union[DataArray, Dataset], key: Union[str, List[str]]):
+def _get_dims(obj: Union[DataArray, Dataset], key: str):
     return [k for k in _get_all(obj, key) if k in obj.dims]
 
 
-def _get_indexes(obj: Union[DataArray, Dataset], key: Union[str, List[str]]):
+def _get_indexes(obj: Union[DataArray, Dataset], key: str):
     return [k for k in _get_all(obj, key) if k in obj.indexes]
 
 
-def _get_coords(obj: Union[DataArray, Dataset], key: Union[str, List[str]]):
+def _get_coords(obj: Union[DataArray, Dataset], key: str):
     return [k for k in _get_all(obj, key) if k in obj.coords]
 
 
 #: Default mappers for common keys.
 _DEFAULT_KEY_MAPPERS: Mapping[str, Tuple[Mapper, ...]] = {
-    "dim": (_get_dims,),  # (_get_axis_coord, _get_with_standard_name),
-    "dims": (_get_dims,),  # (_get_axis_coord, _get_with_standard_name),  # transpose
+    "dim": (_get_dims,),
+    "dims": (_get_dims,),  # transpose
     "drop_dims": (_get_dims,),  # drop_dims
     "dimensions": (_get_dims,),  # stack
     "dims_dict": (_get_dims,),  # swap_dims, rename_dims

From f46222655d58b80c1015b5d081680041f75414b8 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Fri, 12 Feb 2021 19:23:02 +0000
Subject: [PATCH 04/22] add single decorator

---
 cf_xarray/accessor.py            | 43 ++++++++++++++++----------------
 cf_xarray/tests/test_accessor.py |  1 +
 2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index f9eaf6db..a81792c1 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -3,6 +3,7 @@
 import itertools
 import warnings
 from collections import ChainMap
+from functools import wraps
 from typing import (
     Any,
     Callable,
@@ -249,9 +250,7 @@ def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List
         return []
 
 
-def _get_axis_coord(
-    var: Union[DataArray, Dataset], key: str, error: bool = True
-) -> List[str]:
+def _get_axis_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     Translate from axis or coord name to variable name
 
@@ -285,7 +284,7 @@ def _get_axis_coord(
     """
 
     valid_keys = _COORD_NAMES + _AXIS_NAMES
-    if error and key not in valid_keys:
+    if key not in valid_keys:
         raise KeyError(
             f"cf_xarray did not understand key {key!r}. Expected one of {valid_keys!r}"
         )
@@ -315,20 +314,6 @@ def _get_axis_coord(
     return list(results)
 
 
-def _get_single(var: Union[DataArray, Dataset], key: str, func):
-
-    results = func(var, key)
-
-    if len(results) > 1:
-        raise KeyError(
-            f"Multiple results for {key!r} found: {results!r}. I expected only one."
-        )
-    elif len(results) == 0:
-        raise KeyError(f"No results found for {key!r}.")
-
-    return results
-
-
 def _get_measure_variable(
     da: DataArray, key: str, error: bool = True, default: str = None
 ) -> List[DataArray]:
@@ -406,6 +391,21 @@ def _get_coords(obj: Union[DataArray, Dataset], key: str):
     return [k for k in _get_all(obj, key) if k in obj.coords]
 
 
+def _single(func):
+    @wraps(func)
+    def get_single(obj: Union[DataArray, Dataset], key: str):
+        results = func(obj, key)
+        if len(results) > 1:
+            raise KeyError(
+                f"Multiple results for {key!r} found: {results!r}. I expected only one."
+            )
+        elif len(results) == 0:
+            raise KeyError(f"No results found for {key!r}.")
+        return results
+
+    return get_single
+
+
 #: Default mappers for common keys.
 _DEFAULT_KEY_MAPPERS: Mapping[str, Tuple[Mapper, ...]] = {
     "dim": (_get_dims,),
@@ -423,8 +423,8 @@ def _get_coords(obj: Union[DataArray, Dataset], key: str):
     "dims_or_levels": (_get_dims,),  # reset_index
     "window": (_get_dims,),  # rolling_exp
     "coord": (_get_axis_coord_single,),  # differentiate, integrate
-    "group": (_get_all, _get_groupby_time_accessor),  # groupby
-    "indexer": (_get_indexes,),  # resample
+    "group": (_single(_get_all), _get_groupby_time_accessor),  # groupby
+    "indexer": (_single(_get_indexes),),  # resample
     "variables": (_get_all,),  # sortby
     "weights": (_get_measure_variable,),  # type: ignore
     "chunks": (_get_dims,),  # chunk
@@ -466,6 +466,7 @@ def _build_docstring(func):
         _get_groupby_time_accessor: "Time variable accessor e.g. 'T.month'",
         _get_with_standard_name: "Standard names",
         _get_measure_variable: f"One of {_CELL_MEASURES!r}",
+        _single(_get_all): get_all_docstring.replace("One or more of", "One of"),
         _get_all: get_all_docstring,
         _get_indexes: get_all_docstring + "present in .indexes",
         _get_dims: get_all_docstring + "present in .dims",
@@ -477,7 +478,7 @@ def _build_docstring(func):
     for k in set(sig.parameters.keys()) & set(_DEFAULT_KEY_MAPPERS):
         mappers = _DEFAULT_KEY_MAPPERS.get(k, [])
         docstring = ";\n\t\t\t".join(
-            mapper_docstrings.get(mapper, "unknown. please open an issue.")
+            mapper_docstrings.get(id(mapper), "unknown. please open an issue.")
             for mapper in mappers
         )
         string += f"\t\t{k}: {docstring} \n"
diff --git a/cf_xarray/tests/test_accessor.py b/cf_xarray/tests/test_accessor.py
index af8e5570..4392261f 100644
--- a/cf_xarray/tests/test_accessor.py
+++ b/cf_xarray/tests/test_accessor.py
@@ -624,6 +624,7 @@ def test_get_bounds_dim_name():
 
 
 def test_docstring():
+    print(airds.cf.groupby.__doc__)
     assert "One of ('X'" in airds.cf.groupby.__doc__
     assert "One or more of ('X'" in airds.cf.mean.__doc__
 

From be74e466e9c6d4577a791224349f3a67ee750d39 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Fri, 12 Feb 2021 19:25:31 +0000
Subject: [PATCH 05/22] remove id()

---
 cf_xarray/accessor.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index a81792c1..e59c4020 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -478,7 +478,7 @@ def _build_docstring(func):
     for k in set(sig.parameters.keys()) & set(_DEFAULT_KEY_MAPPERS):
         mappers = _DEFAULT_KEY_MAPPERS.get(k, [])
         docstring = ";\n\t\t\t".join(
-            mapper_docstrings.get(id(mapper), "unknown. please open an issue.")
+            mapper_docstrings.get(mapper, "unknown. please open an issue.")
             for mapper in mappers
         )
         string += f"\t\t{k}: {docstring} \n"

From 4cab0c801a35627d53f57ddd901ebe5529e44e09 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sat, 20 Feb 2021 15:54:05 +0000
Subject: [PATCH 06/22] fix docstring and more decorators

---
 cf_xarray/accessor.py | 117 +++++++++++++++++++++++-------------------
 1 file changed, 64 insertions(+), 53 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index e59c4020..364d607c 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -3,7 +3,6 @@
 import itertools
 import warnings
 from collections import ChainMap
-from functools import wraps
 from typing import (
     Any,
     Callable,
@@ -250,6 +249,9 @@ def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List
         return []
 
 
+_get_groupby_time_accessor.__doc__ = "Time variable accessor e.g. 'T.month'"
+
+
 def _get_axis_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     Translate from axis or coord name to variable name
@@ -314,16 +316,6 @@ def _get_axis_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
     return list(results)
 
 
-def _get_measure_variable(
-    da: DataArray, key: str, error: bool = True, default: str = None
-) -> List[DataArray]:
-    """ tiny wrapper since xarray does not support providing str for weights."""
-    varnames = apply_mapper(_get_measure, da, key, error, default)
-    if len(varnames) > 1:
-        raise KeyError(f"Multiple measures found for key {key!r}: {varnames!r}.")
-    return [da[varnames[0]]]
-
-
 def _get_measure(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     Translate from cell measures to appropriate variable name.
@@ -358,6 +350,11 @@ def _get_measure(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return list(results)
 
 
+_get_measure.__doc__ = (
+    f"One or more of {_CELL_MEASURES!r};" "\n\t\t\tor arbitraty measures"
+)
+
+
 def _get_with_standard_name(
     obj: Union[DataArray, Dataset], name: Union[str, List[str]]
 ) -> List[str]:
@@ -379,20 +376,49 @@ def _get_all(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return results
 
 
-def _get_dims(obj: Union[DataArray, Dataset], key: str):
-    return [k for k in _get_all(obj, key) if k in obj.dims]
+_get_all.__doc__ = (
+    f"One or more of {(_AXIS_NAMES + _COORD_NAMES + _CELL_MEASURES)!r};"
+    "\n\t\t\tor arbitraty measures, or standard names"
+)
+
+
+def _dims(func):
+    @functools.wraps(func)
+    def get_dims(obj: Union[DataArray, Dataset], key: str):
+        return [k for k in func(obj, key) if k in obj.dims]
+
+    get_dims.__doc__ = func.__doc__ + " present in .dims"
+    return get_dims
+
+
+def _indexes(func):
+    @functools.wraps(func)
+    def get_indexes(obj: Union[DataArray, Dataset], key: str):
+        return [k for k in func(obj, key) if k in obj.dims]
+
+    get_indexes.__doc__ = func.__doc__ + " present in .indexes"
+    return get_indexes
+
+
+def _coords(func):
+    @functools.wraps(func)
+    def get_coords(obj: Union[DataArray, Dataset], key: str):
+        return [k for k in func(obj, key) if k in obj.coords]
 
+    get_coords.__doc__ = func.__doc__ + " present in .coords"
+    return get_coords
 
-def _get_indexes(obj: Union[DataArray, Dataset], key: str):
-    return [k for k in _get_all(obj, key) if k in obj.indexes]
 
+def _variables(func):
+    @functools.wraps(func)
+    def get_variables(obj: Union[DataArray, Dataset], key: str):
+        return [obj[k] for k in func(obj, key)]
 
-def _get_coords(obj: Union[DataArray, Dataset], key: str):
-    return [k for k in _get_all(obj, key) if k in obj.coords]
+    return get_variables
 
 
 def _single(func):
-    @wraps(func)
+    @functools.wraps(func)
     def get_single(obj: Union[DataArray, Dataset], key: str):
         results = func(obj, key)
         if len(results) > 1:
@@ -403,31 +429,33 @@ def get_single(obj: Union[DataArray, Dataset], key: str):
             raise KeyError(f"No results found for {key!r}.")
         return results
 
+    get_single.__doc__ = func.__doc__.replace("One or more of", "One of")
+
     return get_single
 
 
 #: Default mappers for common keys.
 _DEFAULT_KEY_MAPPERS: Mapping[str, Tuple[Mapper, ...]] = {
-    "dim": (_get_dims,),
-    "dims": (_get_dims,),  # transpose
-    "drop_dims": (_get_dims,),  # drop_dims
-    "dimensions": (_get_dims,),  # stack
-    "dims_dict": (_get_dims,),  # swap_dims, rename_dims
-    "shifts": (_get_dims,),  # shift, roll
-    "pad_width": (_get_dims,),  # shift, roll
+    "dim": (_dims(_get_all),),
+    "dims": (_dims(_get_all),),  # transpose
+    "drop_dims": (_dims(_get_all),),  # drop_dims
+    "dimensions": (_dims(_get_all),),  # stack
+    "dims_dict": (_dims(_get_all),),  # swap_dims, rename_dims
+    "shifts": (_dims(_get_all),),  # shift, roll
+    "pad_width": (_dims(_get_all),),  # shift, roll
     "names": (_get_all,),  # set_coords, reset_coords, drop_vars
-    "labels": (_get_indexes,),  # drop_sel
-    "coords": (_get_dims,),  # interp
-    "indexers": (_get_indexes,),  # sel, isel, reindex
+    "labels": (_indexes(_get_all),),  # drop_sel
+    "coords": (_dims(_get_all),),  # interp
+    "indexers": (_dims(_get_all),),  # sel, isel, reindex
     # "indexes": (_get_axis_coord,),  # set_index
-    "dims_or_levels": (_get_dims,),  # reset_index
-    "window": (_get_dims,),  # rolling_exp
-    "coord": (_get_axis_coord_single,),  # differentiate, integrate
+    "dims_or_levels": (_dims(_get_all),),  # reset_index
+    "window": (_dims(_get_all),),  # rolling_exp
+    "coord": (_single(_coords(_get_all)),),  # differentiate, integrate
     "group": (_single(_get_all), _get_groupby_time_accessor),  # groupby
-    "indexer": (_single(_get_indexes),),  # resample
+    "indexer": (_single(_indexes(_get_all)),),  # resample
     "variables": (_get_all,),  # sortby
-    "weights": (_get_measure_variable,),  # type: ignore
-    "chunks": (_get_dims,),  # chunk
+    "weights": (_variables(_single(_get_all)),),  # type: ignore
+    "chunks": (_dims(_get_all),),  # chunk
 }
 
 
@@ -456,36 +484,19 @@ def _build_docstring(func):
     can be used for arguments.
     """
 
-    get_all_docstring = (
-        f"One or more of {(_AXIS_NAMES + _COORD_NAMES)!r};\n\t\t\tor standard names"
-    )
-    # this list will need to be updated any time a new mapper is added
-    mapper_docstrings = {
-        _get_axis_coord: f"One or more of {(_AXIS_NAMES + _COORD_NAMES)!r}",
-        _get_axis_coord_single: f"One of {(_AXIS_NAMES + _COORD_NAMES)!r}",
-        _get_groupby_time_accessor: "Time variable accessor e.g. 'T.month'",
-        _get_with_standard_name: "Standard names",
-        _get_measure_variable: f"One of {_CELL_MEASURES!r}",
-        _single(_get_all): get_all_docstring.replace("One or more of", "One of"),
-        _get_all: get_all_docstring,
-        _get_indexes: get_all_docstring + "present in .indexes",
-        _get_dims: get_all_docstring + "present in .dims",
-        _get_coords: get_all_docstring + "present in .coords",
-    }
-
     sig = inspect.signature(func)
     string = ""
     for k in set(sig.parameters.keys()) & set(_DEFAULT_KEY_MAPPERS):
         mappers = _DEFAULT_KEY_MAPPERS.get(k, [])
         docstring = ";\n\t\t\t".join(
-            mapper_docstrings.get(mapper, "unknown. please open an issue.")
+            mapper.__doc__ if mapper.__doc__ else "unknown. please open an issue."
             for mapper in mappers
         )
         string += f"\t\t{k}: {docstring} \n"
 
     for param in sig.parameters:
         if sig.parameters[param].kind is inspect.Parameter.VAR_KEYWORD:
-            string += f"\t\t{param}: {mapper_docstrings[_get_axis_coord]} \n\n"
+            string += f"\t\t{param}: {_get_all.__doc__} \n\n"
     return (
         f"\n\tThe following arguments will be processed by cf_xarray: \n{string}"
         "\n\t----\n\t"

From f30e7fe62d18f3fa84ed27ac044b5d0559a6f761 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sat, 20 Feb 2021 16:58:28 +0000
Subject: [PATCH 07/22] back to undecorated

---
 cf_xarray/accessor.py | 60 +++++++++++++++++++------------------------
 1 file changed, 27 insertions(+), 33 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 364d607c..b4256d86 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -382,31 +382,25 @@ def _get_all(obj: Union[DataArray, Dataset], key: str) -> List[str]:
 )
 
 
-def _dims(func):
-    @functools.wraps(func)
-    def get_dims(obj: Union[DataArray, Dataset], key: str):
-        return [k for k in func(obj, key) if k in obj.dims]
+def _get_dims(obj: Union[DataArray, Dataset], key: str):
+    return [k for k in _get_all(obj, key) if k in obj.dims]
 
-    get_dims.__doc__ = func.__doc__ + " present in .dims"
-    return get_dims
 
+_get_dims.__doc__ = _get_all.__doc__ + " present in .dims"
 
-def _indexes(func):
-    @functools.wraps(func)
-    def get_indexes(obj: Union[DataArray, Dataset], key: str):
-        return [k for k in func(obj, key) if k in obj.dims]
 
-    get_indexes.__doc__ = func.__doc__ + " present in .indexes"
-    return get_indexes
+def _get_indexes(obj: Union[DataArray, Dataset], key: str):
+    return [k for k in _get_all(obj, key) if k in obj.indexes]
 
 
-def _coords(func):
-    @functools.wraps(func)
-    def get_coords(obj: Union[DataArray, Dataset], key: str):
-        return [k for k in func(obj, key) if k in obj.coords]
+_get_indexes.__doc__ = _get_all.__doc__ + " present in .indexes"
+
+
+def _get_coords(obj: Union[DataArray, Dataset], key: str):
+    return [k for k in _get_all(obj, key) if k in obj.coords]
+
 
-    get_coords.__doc__ = func.__doc__ + " present in .coords"
-    return get_coords
+_get_coords.__doc__ = _get_all.__doc__ + " present in .coords"
 
 
 def _variables(func):
@@ -436,26 +430,26 @@ def get_single(obj: Union[DataArray, Dataset], key: str):
 
 #: Default mappers for common keys.
 _DEFAULT_KEY_MAPPERS: Mapping[str, Tuple[Mapper, ...]] = {
-    "dim": (_dims(_get_all),),
-    "dims": (_dims(_get_all),),  # transpose
-    "drop_dims": (_dims(_get_all),),  # drop_dims
-    "dimensions": (_dims(_get_all),),  # stack
-    "dims_dict": (_dims(_get_all),),  # swap_dims, rename_dims
-    "shifts": (_dims(_get_all),),  # shift, roll
-    "pad_width": (_dims(_get_all),),  # shift, roll
+    "dim": (_get_dims,),
+    "dims": (_get_dims,),  # transpose
+    "drop_dims": (_get_dims,),  # drop_dims
+    "dimensions": (_get_dims,),  # stack
+    "dims_dict": (_get_dims,),  # swap_dims, rename_dims
+    "shifts": (_get_dims,),  # shift, roll
+    "pad_width": (_get_dims,),  # shift, roll
     "names": (_get_all,),  # set_coords, reset_coords, drop_vars
-    "labels": (_indexes(_get_all),),  # drop_sel
-    "coords": (_dims(_get_all),),  # interp
-    "indexers": (_dims(_get_all),),  # sel, isel, reindex
+    "labels": (_get_indexes,),  # drop_sel
+    "coords": (_get_dims,),  # interp
+    "indexers": (_get_dims,),  # sel, isel, reindex
     # "indexes": (_get_axis_coord,),  # set_index
-    "dims_or_levels": (_dims(_get_all),),  # reset_index
-    "window": (_dims(_get_all),),  # rolling_exp
-    "coord": (_single(_coords(_get_all)),),  # differentiate, integrate
+    "dims_or_levels": (_get_dims,),  # reset_index
+    "window": (_get_dims,),  # rolling_exp
+    "coord": (_single(_get_coords),),  # differentiate, integrate
     "group": (_single(_get_all), _get_groupby_time_accessor),  # groupby
-    "indexer": (_single(_indexes(_get_all)),),  # resample
+    "indexer": (_single(_get_indexes),),  # resample
     "variables": (_get_all,),  # sortby
     "weights": (_variables(_single(_get_all)),),  # type: ignore
-    "chunks": (_dims(_get_all),),  # chunk
+    "chunks": (_get_dims,),  # chunk
 }
 
 

From 7525a2a5472a603c1f6a1f88fdc0f59bd9b2dd28 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sat, 20 Feb 2021 18:24:04 +0000
Subject: [PATCH 08/22] replace _get_axis_coord_single

---
 cf_xarray/accessor.py | 24 ++++++------------------
 1 file changed, 6 insertions(+), 18 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index b4256d86..ce999158 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -203,18 +203,6 @@ def _apply_single_mapper(mapper):
     return results
 
 
-def _get_axis_coord_single(var: Union[DataArray, Dataset], key: str) -> List[str]:
-    """ Helper method for when we really want only one result per key. """
-    results = _get_axis_coord(var, key)
-    if len(results) > 1:
-        raise KeyError(
-            f"Multiple results for {key!r} found: {results!r}. I expected only one."
-        )
-    elif len(results) == 0:
-        raise KeyError(f"No results found for {key!r}.")
-    return results
-
-
 def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     Helper method for when our key name is of the nature "T.month" and we want to
@@ -826,7 +814,7 @@ def __call__(self, *args, **kwargs):
             obj=self._obj,
             attr="plot",
             accessor=self.accessor,
-            key_mappers=dict.fromkeys(self._keys, (_get_axis_coord_single,)),
+            key_mappers=dict.fromkeys(self._keys, (_single(_get_all),)),
         )
         return self._plot_decorator(plot)(*args, **kwargs)
 
@@ -838,7 +826,7 @@ def __getattr__(self, attr):
             obj=self._obj.plot,
             attr=attr,
             accessor=self.accessor,
-            key_mappers=dict.fromkeys(self._keys, (_get_axis_coord_single,)),
+            key_mappers=dict.fromkeys(self._keys, (_single(_get_all),)),
             # TODO: "extra_decorator" is more complex than I would like it to be.
             # Not sure if there is a better way though
             extra_decorator=self._plot_decorator,
@@ -1001,7 +989,7 @@ def _rewrite_values(
             if vkw in kwargs:
                 maybe_update = {
                     # TODO: this is assuming key_mappers[k] is always
-                    # _get_axis_coord_single
+                    # _single(_get_all)
                     k: apply_mapper(
                         key_mappers[k], self._obj, v, error=False, default=[v]
                     )[0]
@@ -1357,8 +1345,8 @@ def rename_like(
 
         renamer = {}
         for key in good_keys:
-            ours = _get_axis_coord_single(self._obj, key)[0]
-            theirs = _get_axis_coord_single(other, key)[0]
+            ours = _single(_get_all)(self._obj, key)[0]
+            theirs = _single(_get_all)(other, key)[0]
             renamer[ours] = theirs
 
         newobj = self._obj.rename(renamer)
@@ -1467,7 +1455,7 @@ def get_bounds(self, key: str) -> DataArray:
         DataArray
         """
         name = apply_mapper(
-            _get_axis_coord_single, self._obj, key, error=False, default=[key]
+            _single(_get_all), self._obj, key, error=False, default=[key]
         )[0]
         bounds = self._obj[name].attrs["bounds"]
         obj = self._maybe_to_dataset()

From 11b3ef7053780f30999538142df9673799daaa2d Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sat, 20 Feb 2021 18:57:42 +0000
Subject: [PATCH 09/22] use _get_coords for plot()

---
 cf_xarray/accessor.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index ce999158..82c8ef2b 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -814,7 +814,7 @@ def __call__(self, *args, **kwargs):
             obj=self._obj,
             attr="plot",
             accessor=self.accessor,
-            key_mappers=dict.fromkeys(self._keys, (_single(_get_all),)),
+            key_mappers=dict.fromkeys(self._keys, (_single(_get_coords),)),
         )
         return self._plot_decorator(plot)(*args, **kwargs)
 

From f5ff3c9f34f054d70544567adab8a6a6de915c05 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sat, 20 Feb 2021 19:35:53 +0000
Subject: [PATCH 10/22] better type check

---
 cf_xarray/accessor.py | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 82c8ef2b..6565c842 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -15,7 +15,9 @@
     Optional,
     Set,
     Tuple,
+    TypeVar,
     Union,
+    cast
 )
 
 import xarray as xr
@@ -145,6 +147,9 @@
 # Type for Mapper functions
 Mapper = Callable[[Union[DataArray, Dataset], str], List[str]]
 
+# Type for decorators
+F = TypeVar("F", bound=Callable[..., Any])
+
 
 def apply_mapper(
     mappers: Union[Mapper, Tuple[Mapper, ...]],
@@ -370,38 +375,38 @@ def _get_all(obj: Union[DataArray, Dataset], key: str) -> List[str]:
 )
 
 
-def _get_dims(obj: Union[DataArray, Dataset], key: str):
+def _get_dims(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return [k for k in _get_all(obj, key) if k in obj.dims]
 
 
 _get_dims.__doc__ = _get_all.__doc__ + " present in .dims"
 
 
-def _get_indexes(obj: Union[DataArray, Dataset], key: str):
+def _get_indexes(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return [k for k in _get_all(obj, key) if k in obj.indexes]
 
 
 _get_indexes.__doc__ = _get_all.__doc__ + " present in .indexes"
 
 
-def _get_coords(obj: Union[DataArray, Dataset], key: str):
+def _get_coords(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return [k for k in _get_all(obj, key) if k in obj.coords]
 
 
 _get_coords.__doc__ = _get_all.__doc__ + " present in .coords"
 
 
-def _variables(func):
+def _variables(func: F) -> F:
     @functools.wraps(func)
-    def get_variables(obj: Union[DataArray, Dataset], key: str):
+    def wrapper(obj: Union[DataArray, Dataset], key: str) -> List[DataArray]:
         return [obj[k] for k in func(obj, key)]
 
-    return get_variables
+    return cast(F, wrapper)
 
 
-def _single(func):
+def _single(func: F) -> F:
     @functools.wraps(func)
-    def get_single(obj: Union[DataArray, Dataset], key: str):
+    def wrapper(obj: Union[DataArray, Dataset], key: str):
         results = func(obj, key)
         if len(results) > 1:
             raise KeyError(
@@ -411,9 +416,9 @@ def get_single(obj: Union[DataArray, Dataset], key: str):
             raise KeyError(f"No results found for {key!r}.")
         return results
 
-    get_single.__doc__ = func.__doc__.replace("One or more of", "One of")
+    wrapper.__doc__ = func.__doc__.replace("One or more of", "One of") if func.__doc__ else func.__doc__
 
-    return get_single
+    return cast(F, wrapper)
 
 
 #: Default mappers for common keys.

From 8c91cf9dc3dc378ffd07a93466f992f0d226ec22 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sat, 20 Feb 2021 19:38:10 +0000
Subject: [PATCH 11/22] run pre-commit

---
 cf_xarray/accessor.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 6565c842..ec074e1a 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -17,7 +17,7 @@
     Tuple,
     TypeVar,
     Union,
-    cast
+    cast,
 )
 
 import xarray as xr
@@ -416,7 +416,11 @@ def wrapper(obj: Union[DataArray, Dataset], key: str):
             raise KeyError(f"No results found for {key!r}.")
         return results
 
-    wrapper.__doc__ = func.__doc__.replace("One or more of", "One of") if func.__doc__ else func.__doc__
+    wrapper.__doc__ = (
+        func.__doc__.replace("One or more of", "One of")
+        if func.__doc__
+        else func.__doc__
+    )
 
     return cast(F, wrapper)
 

From 49fe808766fc4b0b576248985dcc62b834f3e521 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sat, 20 Feb 2021 22:27:38 +0000
Subject: [PATCH 12/22] wrap doc and use coords for plot.*

---
 cf_xarray/accessor.py           | 49 +++++++++++++++------------------
 doc/examples/introduction.ipynb |  2 +-
 2 files changed, 23 insertions(+), 28 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index ec074e1a..322e02b0 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -208,6 +208,19 @@ def _apply_single_mapper(mapper):
     return results
 
 
+def _set_doc(doc):
+    def decorator(func):
+        @functools.wraps(func)
+        def wrapper(*args, **kwargs):
+            return func(*args, **kwargs)
+
+        wrapper.__doc__ = doc
+        return cast(F, wrapper)
+
+    return decorator
+
+
+@_set_doc("Time variable accessor e.g. 'T.month'")
 def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     Helper method for when our key name is of the nature "T.month" and we want to
@@ -231,9 +244,7 @@ def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List
     if "." in key:
         key, ext = key.split(".", 1)
 
-        results = apply_mapper(
-            (_get_axis_coord, _get_with_standard_name), var, key, error=False
-        )
+        results = apply_mapper((_get_all,), var, key, error=False)
         if len(results) > 1:
             raise KeyError(f"Multiple results received for {key}.")
         return [v + "." + ext for v in results]
@@ -242,9 +253,6 @@ def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List
         return []
 
 
-_get_groupby_time_accessor.__doc__ = "Time variable accessor e.g. 'T.month'"
-
-
 def _get_axis_coord(var: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     Translate from axis or coord name to variable name
@@ -343,11 +351,6 @@ def _get_measure(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return list(results)
 
 
-_get_measure.__doc__ = (
-    f"One or more of {_CELL_MEASURES!r};" "\n\t\t\tor arbitraty measures"
-)
-
-
 def _get_with_standard_name(
     obj: Union[DataArray, Dataset], name: Union[str, List[str]]
 ) -> List[str]:
@@ -363,39 +366,31 @@ def _get_with_standard_name(
     return varnames
 
 
+@_set_doc(
+    f"One or more of {(_AXIS_NAMES + _COORD_NAMES + _CELL_MEASURES)!r},"
+    "\n\t\t\tor arbitraty measures, or standard names"
+)
 def _get_all(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     all_mappers = (_get_axis_coord, _get_measure, _get_with_standard_name)
     results = apply_mapper(all_mappers, obj, key, error=False, default=None)
     return results
 
 
-_get_all.__doc__ = (
-    f"One or more of {(_AXIS_NAMES + _COORD_NAMES + _CELL_MEASURES)!r};"
-    "\n\t\t\tor arbitraty measures, or standard names"
-)
-
-
+@_set_doc(_get_all.__doc__ + " present in .dims")
 def _get_dims(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return [k for k in _get_all(obj, key) if k in obj.dims]
 
 
-_get_dims.__doc__ = _get_all.__doc__ + " present in .dims"
-
-
+@_set_doc(_get_all.__doc__ + " present in .indexes")
 def _get_indexes(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return [k for k in _get_all(obj, key) if k in obj.indexes]
 
 
-_get_indexes.__doc__ = _get_all.__doc__ + " present in .indexes"
-
-
+@_set_doc(_get_all.__doc__ + " present in .coords")
 def _get_coords(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     return [k for k in _get_all(obj, key) if k in obj.coords]
 
 
-_get_coords.__doc__ = _get_all.__doc__ + " present in .coords"
-
-
 def _variables(func: F) -> F:
     @functools.wraps(func)
     def wrapper(obj: Union[DataArray, Dataset], key: str) -> List[DataArray]:
@@ -835,7 +830,7 @@ def __getattr__(self, attr):
             obj=self._obj.plot,
             attr=attr,
             accessor=self.accessor,
-            key_mappers=dict.fromkeys(self._keys, (_single(_get_all),)),
+            key_mappers=dict.fromkeys(self._keys, (_single(_get_coords),)),
             # TODO: "extra_decorator" is more complex than I would like it to be.
             # Not sure if there is a better way though
             extra_decorator=self._plot_decorator,
diff --git a/doc/examples/introduction.ipynb b/doc/examples/introduction.ipynb
index 3a7c1c94..87d0f3bb 100644
--- a/doc/examples/introduction.ipynb
+++ b/doc/examples/introduction.ipynb
@@ -982,7 +982,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.8"
+   "version": "3.9.1"
   },
   "toc": {
    "base_numbering": 1,

From 425c4720d83c97a17f509c3ce4977bcec301ef64 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sun, 21 Feb 2021 07:43:54 +0000
Subject: [PATCH 13/22] explicitly write docs

---
 cf_xarray/accessor.py            | 44 +++++++++++++++-----------------
 cf_xarray/tests/test_accessor.py | 19 +++++++++++++-
 2 files changed, 39 insertions(+), 24 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 322e02b0..d46da8b0 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -208,20 +208,10 @@ def _apply_single_mapper(mapper):
     return results
 
 
-def _set_doc(doc):
-    def decorator(func):
-        @functools.wraps(func)
-        def wrapper(*args, **kwargs):
-            return func(*args, **kwargs)
-
-        wrapper.__doc__ = doc
-        return cast(F, wrapper)
-
-    return decorator
-
-
-@_set_doc("Time variable accessor e.g. 'T.month'")
 def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List[str]:
+    """
+    Time variable accessor e.g. 'T.month'
+    """
     """
     Helper method for when our key name is of the nature "T.month" and we want to
     isolate the "T" for coordinate mapping
@@ -241,6 +231,7 @@ def _get_groupby_time_accessor(var: Union[DataArray, Dataset], key: str) -> List
     -----
     Returns an empty list if there is no frequency extension specified.
     """
+
     if "." in key:
         key, ext = key.split(".", 1)
 
@@ -366,28 +357,37 @@ def _get_with_standard_name(
     return varnames
 
 
-@_set_doc(
-    f"One or more of {(_AXIS_NAMES + _COORD_NAMES + _CELL_MEASURES)!r},"
-    "\n\t\t\tor arbitraty measures, or standard names"
-)
 def _get_all(obj: Union[DataArray, Dataset], key: str) -> List[str]:
+    """
+    One or more of ('X', 'Y', 'Z', 'T', 'longitude', 'latitude', 'vertical', 'time',
+    'area', 'volume'), or arbitraty measures, or standard names
+    """
     all_mappers = (_get_axis_coord, _get_measure, _get_with_standard_name)
     results = apply_mapper(all_mappers, obj, key, error=False, default=None)
     return results
 
 
-@_set_doc(_get_all.__doc__ + " present in .dims")
 def _get_dims(obj: Union[DataArray, Dataset], key: str) -> List[str]:
+    """
+    One or more of ('X', 'Y', 'Z', 'T', 'longitude', 'latitude', 'vertical', 'time',
+    'area', 'volume'), or arbitraty measures, or standard names present in .dims
+    """
     return [k for k in _get_all(obj, key) if k in obj.dims]
 
 
-@_set_doc(_get_all.__doc__ + " present in .indexes")
 def _get_indexes(obj: Union[DataArray, Dataset], key: str) -> List[str]:
+    """
+    One or more of ('X', 'Y', 'Z', 'T', 'longitude', 'latitude', 'vertical', 'time',
+    'area', 'volume'), or arbitraty measures, or standard names present in .indexes
+    """
     return [k for k in _get_all(obj, key) if k in obj.indexes]
 
 
-@_set_doc(_get_all.__doc__ + " present in .coords")
 def _get_coords(obj: Union[DataArray, Dataset], key: str) -> List[str]:
+    """
+    One or more of ('X', 'Y', 'Z', 'T', 'longitude', 'latitude', 'vertical', 'time',
+    'area', 'volume'), or arbitraty measures, or standard names present in .coords
+    """
     return [k for k in _get_all(obj, key) if k in obj.coords]
 
 
@@ -830,7 +830,7 @@ def __getattr__(self, attr):
             obj=self._obj.plot,
             attr=attr,
             accessor=self.accessor,
-            key_mappers=dict.fromkeys(self._keys, (_single(_get_coords),)),
+            key_mappers=dict.fromkeys(self._keys, (_single(_get_all),)),
             # TODO: "extra_decorator" is more complex than I would like it to be.
             # Not sure if there is a better way though
             extra_decorator=self._plot_decorator,
@@ -992,8 +992,6 @@ def _rewrite_values(
         for vkw in var_kws:
             if vkw in kwargs:
                 maybe_update = {
-                    # TODO: this is assuming key_mappers[k] is always
-                    # _single(_get_all)
                     k: apply_mapper(
                         key_mappers[k], self._obj, v, error=False, default=[v]
                     )[0]
diff --git a/cf_xarray/tests/test_accessor.py b/cf_xarray/tests/test_accessor.py
index 4392261f..1e697cbe 100644
--- a/cf_xarray/tests/test_accessor.py
+++ b/cf_xarray/tests/test_accessor.py
@@ -624,9 +624,26 @@ def test_get_bounds_dim_name():
 
 
 def test_docstring():
-    print(airds.cf.groupby.__doc__)
     assert "One of ('X'" in airds.cf.groupby.__doc__
+    assert "Time variable accessor e.g. 'T.month'" in airds.cf.groupby.__doc__
     assert "One or more of ('X'" in airds.cf.mean.__doc__
+    assert "present in .dims" in airds.cf.drop_dims.__doc__
+    assert "present in .coords" in airds.cf.integrate.__doc__
+    assert "present in .indexes" in airds.cf.resample.__doc__
+
+    # Make sure docs are up to date
+    get_all_doc = cf_xarray.accessor._get_all.__doc__
+    all_keys = (
+        cf_xarray.accessor._AXIS_NAMES
+        + cf_xarray.accessor._COORD_NAMES
+        + cf_xarray.accessor._CELL_MEASURES
+    )
+    expected = f"One or more of {all_keys!r}, or arbitraty measures, or standard names"
+    assert get_all_doc.split() == expected.split()
+    for name in ["dims", "indexes", "coords"]:
+        actual = getattr(cf_xarray.accessor, f"_get_{name}").__doc__
+        expected = get_all_doc + f" present in .{name}"
+        assert actual.split() == expected.split()
 
 
 def _make_names(prefixes):

From e8b673e2b702706301069efae46267c78cbc64af Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sun, 21 Feb 2021 08:00:15 +0000
Subject: [PATCH 14/22] fix typo

---
 cf_xarray/accessor.py            | 8 ++++----
 cf_xarray/tests/test_accessor.py | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index d46da8b0..447f5dd1 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -360,7 +360,7 @@ def _get_with_standard_name(
 def _get_all(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     One or more of ('X', 'Y', 'Z', 'T', 'longitude', 'latitude', 'vertical', 'time',
-    'area', 'volume'), or arbitraty measures, or standard names
+    'area', 'volume'), or arbitrary measures, or standard names
     """
     all_mappers = (_get_axis_coord, _get_measure, _get_with_standard_name)
     results = apply_mapper(all_mappers, obj, key, error=False, default=None)
@@ -370,7 +370,7 @@ def _get_all(obj: Union[DataArray, Dataset], key: str) -> List[str]:
 def _get_dims(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     One or more of ('X', 'Y', 'Z', 'T', 'longitude', 'latitude', 'vertical', 'time',
-    'area', 'volume'), or arbitraty measures, or standard names present in .dims
+    'area', 'volume'), or arbitrary measures, or standard names present in .dims
     """
     return [k for k in _get_all(obj, key) if k in obj.dims]
 
@@ -378,7 +378,7 @@ def _get_dims(obj: Union[DataArray, Dataset], key: str) -> List[str]:
 def _get_indexes(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     One or more of ('X', 'Y', 'Z', 'T', 'longitude', 'latitude', 'vertical', 'time',
-    'area', 'volume'), or arbitraty measures, or standard names present in .indexes
+    'area', 'volume'), or arbitrary measures, or standard names present in .indexes
     """
     return [k for k in _get_all(obj, key) if k in obj.indexes]
 
@@ -386,7 +386,7 @@ def _get_indexes(obj: Union[DataArray, Dataset], key: str) -> List[str]:
 def _get_coords(obj: Union[DataArray, Dataset], key: str) -> List[str]:
     """
     One or more of ('X', 'Y', 'Z', 'T', 'longitude', 'latitude', 'vertical', 'time',
-    'area', 'volume'), or arbitraty measures, or standard names present in .coords
+    'area', 'volume'), or arbitrary measures, or standard names present in .coords
     """
     return [k for k in _get_all(obj, key) if k in obj.coords]
 
diff --git a/cf_xarray/tests/test_accessor.py b/cf_xarray/tests/test_accessor.py
index 1e697cbe..1c0527b8 100644
--- a/cf_xarray/tests/test_accessor.py
+++ b/cf_xarray/tests/test_accessor.py
@@ -638,7 +638,7 @@ def test_docstring():
         + cf_xarray.accessor._COORD_NAMES
         + cf_xarray.accessor._CELL_MEASURES
     )
-    expected = f"One or more of {all_keys!r}, or arbitraty measures, or standard names"
+    expected = f"One or more of {all_keys!r}, or arbitrary measures, or standard names"
     assert get_all_doc.split() == expected.split()
     for name in ["dims", "indexes", "coords"]:
         actual = getattr(cf_xarray.accessor, f"_get_{name}").__doc__

From ad88f3f4b12acfa7cbdbd9aacc444b2ac046187c Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Sun, 21 Feb 2021 09:24:34 -0700
Subject: [PATCH 15/22] Fix line plots with .plot

---
 cf_xarray/accessor.py            | 14 +++++++++-----
 cf_xarray/tests/test_accessor.py |  6 ++++++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 447f5dd1..c9dab76c 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -346,6 +346,9 @@ def _get_with_standard_name(
     obj: Union[DataArray, Dataset], name: Union[str, List[str]]
 ) -> List[str]:
     """ returns a list of variable names with standard name == name. """
+    if name is None:
+        return []
+
     varnames = []
     if isinstance(obj, DataArray):
         obj = obj._to_temp_dataset()
@@ -769,9 +772,9 @@ def __init__(self, obj, accessor):
     def _plot_decorator(self, func):
         """
         This decorator is used to set default kwargs on plotting functions.
-
-        For now, this is setting ``xincrease`` and ``yincrease``. It could set
-        other arguments in the future.
+        For now, this can
+        1. set ``xincrease`` and ``yincrease``.
+        2. automatically set ``x`` or ``y``.
         """
         valid_keys = self.accessor.keys()
 
@@ -795,7 +798,8 @@ def _process_x_or_y(kwargs, key):
                 return kwargs
 
             is_line_plot = (func.__name__ == "line") or (
-                func.__name__ == "wrapper" and kwargs.get("hue")
+                func.__name__ == "wrapper"
+                and (kwargs.get("hue") or self._obj.ndim == 1)
             )
             if is_line_plot:
                 if not kwargs.get("hue"):
@@ -818,7 +822,7 @@ def __call__(self, *args, **kwargs):
             obj=self._obj,
             attr="plot",
             accessor=self.accessor,
-            key_mappers=dict.fromkeys(self._keys, (_single(_get_coords),)),
+            key_mappers=dict.fromkeys(self._keys, (_single(_get_all),)),
         )
         return self._plot_decorator(plot)(*args, **kwargs)
 
diff --git a/cf_xarray/tests/test_accessor.py b/cf_xarray/tests/test_accessor.py
index 1c0527b8..5fb34bbb 100644
--- a/cf_xarray/tests/test_accessor.py
+++ b/cf_xarray/tests/test_accessor.py
@@ -413,6 +413,10 @@ def test_dataarray_plot():
     np.testing.assert_equal(rv[0].get_xdata(), obj.lat.data)
     plt.close()
 
+    rv = obj.isel(time=0, lon=1).cf.plot(x="lat")
+    np.testing.assert_equal(rv[0].get_xdata(), obj.lat.data)
+    plt.close()
+
     # various line plots and automatic guessing
     rv = obj.cf.isel(T=1, Y=[0, 1, 2]).cf.plot.line()
     np.testing.assert_equal(rv[0].get_xdata(), obj.lon.data)
@@ -865,6 +869,8 @@ def test_standard_name_mapper():
     expected = da.sortby("label")
     assert_identical(actual, expected)
 
+    assert cf_xarray.accessor._get_with_standard_name(da, None) == []
+
 
 @pytest.mark.parametrize("obj", objects)
 @pytest.mark.parametrize("attr", ["drop_vars", "set_coords"])

From 54b8cc6782e21d06776bd8e2b3786bff8dc3e89b Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Sun, 21 Feb 2021 18:03:03 +0000
Subject: [PATCH 16/22] replace _get_axis_coord

---
 cf_xarray/accessor.py | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index c9dab76c..ed5f982e 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -436,7 +436,7 @@ def wrapper(obj: Union[DataArray, Dataset], key: str):
     "labels": (_get_indexes,),  # drop_sel
     "coords": (_get_dims,),  # interp
     "indexers": (_get_dims,),  # sel, isel, reindex
-    # "indexes": (_get_axis_coord,),  # set_index
+    "indexes": (_get_dims,),  # set_index TODO: cf_xarray decodes keys, not values
     "dims_or_levels": (_get_dims,),  # reset_index
     "window": (_get_dims,),  # rolling_exp
     "coord": (_single(_get_coords),),  # differentiate, integrate
@@ -617,12 +617,12 @@ def check_results(names, k):
     successful = dict.fromkeys(key, False)
     for k in key:
         if "coords" not in skip and k in _AXIS_NAMES + _COORD_NAMES:
-            names = _get_axis_coord(obj, k)
+            names = _get_all(obj, k)
             check_results(names, k)
             successful[k] = bool(names)
             coords.extend(names)
         elif "measures" not in skip and k in accessor._get_all_cell_measures():
-            measure = _get_measure(obj, k)
+            measure = _get_all(obj, k)
             check_results(measure, k)
             successful[k] = bool(measure)
             if measure:
@@ -1145,10 +1145,7 @@ def axes(self) -> Dict[str, List[str]]:
         Dictionary of valid Axis names that can be used with ``__getitem__`` or ``.cf[key]``.
         Will be ("X", "Y", "Z", "T") or a subset thereof.
         """
-        vardict = {
-            key: apply_mapper(_get_axis_coord, self._obj, key, error=False)
-            for key in _AXIS_NAMES
-        }
+        vardict = {key: _get_coords(self._obj, key) for key in _AXIS_NAMES}
 
         return {k: sorted(v) for k, v in vardict.items() if v}
 
@@ -1167,10 +1164,7 @@ def coordinates(self) -> Dict[str, List[str]]:
         Dictionary of valid Coordinate names that can be used with ``__getitem__`` or ``.cf[key]``.
         Will be ("longitude", "latitude", "vertical", "time") or a subset thereof.
         """
-        vardict = {
-            key: apply_mapper(_get_axis_coord, self._obj, key, error=False)
-            for key in _COORD_NAMES
-        }
+        vardict = {key: _get_coords(self._obj, key) for key in _COORD_NAMES}
 
         return {k: sorted(v) for k, v in vardict.items() if v}
 
@@ -1197,10 +1191,10 @@ def cell_measures(self) -> Dict[str, List[str]]:
                 da.attrs.get("cell_measures", "") for da in obj.data_vars.values()
             ]
 
-        measures: Dict[str, List[str]] = {}
+        keys = {}
         for attr in all_attrs:
-            for key, value in parse_cell_methods_attr(attr).items():
-                measures[key] = measures.setdefault(key, []) + [value]
+            keys.update(parse_cell_methods_attr(attr))
+        measures = {key: _get_all(self._obj, key) for key in keys}
 
         return {k: sorted(set(v)) for k, v in measures.items() if v}
 
@@ -1638,7 +1632,7 @@ def decode_vertical_coords(self, prefix="z"):
         import re
 
         ds = self._obj
-        dims = _get_axis_coord(ds, "Z")
+        dims = _get_dims(ds, "Z")
 
         requirements = {
             "ocean_s_coordinate_g1": {"depth_c", "depth", "s", "C", "eta"},

From a3178b501fb0617f02809fd358773b2889787612 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Tue, 23 Feb 2021 08:26:06 +0000
Subject: [PATCH 17/22] update properties dosctring

---
 cf_xarray/accessor.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index ed5f982e..9d0f0b2b 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -1138,7 +1138,7 @@ def axes(self) -> Dict[str, List[str]]:
 
         This is useful for checking whether a key is valid for indexing, i.e.
         that the attributes necessary to allow indexing by that key exist.
-        However, it will only return the Axis names, not Coordinate names.
+        However, it will only return the Axis names present in ``.coords``, not Coordinate names.
 
         Returns
         -------
@@ -1157,7 +1157,7 @@ def coordinates(self) -> Dict[str, List[str]]:
 
         This is useful for checking whether a key is valid for indexing, i.e.
         that the attributes necessary to allow indexing by that key exist.
-        However, it will only return the Coordinate names, not Axis names.
+        However, it will only return the Coordinate names present in ``.coords``, not Axis names.
 
         Returns
         -------

From 7991beeff89191ec991c66402f18dd9db5565986 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Tue, 23 Feb 2021 09:01:01 +0000
Subject: [PATCH 18/22] Copy over #165 tests

---
 cf_xarray/accessor.py            |  7 +------
 cf_xarray/datasets.py            |  3 ++-
 cf_xarray/tests/test_accessor.py | 23 ++++++++++++++++++++---
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 9d0f0b2b..f82cfbfa 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -1337,12 +1337,7 @@ def rename_like(
         ourkeys = self.keys()
         theirkeys = other.cf.keys()
 
-        good_keys = set(_COORD_NAMES) & ourkeys & theirkeys
-        if not good_keys:
-            raise ValueError(
-                "No common coordinate variables between these two objects."
-            )
-
+        good_keys = ourkeys & theirkeys
         renamer = {}
         for key in good_keys:
             ours = _single(_get_all)(self._obj, key)[0]
diff --git a/cf_xarray/datasets.py b/cf_xarray/datasets.py
index fea548bb..5e6df446 100644
--- a/cf_xarray/datasets.py
+++ b/cf_xarray/datasets.py
@@ -70,6 +70,7 @@
 anc["q_detection_limit"] = xr.DataArray(
     1e-3, attrs=dict(standard_name="specific_humidity detection_minimum", units="g/g")
 )
+anc
 
 
 multiple = xr.Dataset()
@@ -121,7 +122,7 @@
 romsds["temp"] = (
     ("ocean_time", "s_rho"),
     [np.linspace(20, 30, 30)] * 2,
-    {"coordinates": "z_rho_dummy"},
+    {"coordinates": "z_rho_dummy", "standard_name": "sea_water_potential_temperature"},
 )
 romsds["temp"].encoding["coordinates"] = "s_rho"
 romsds.coords["z_rho_dummy"] = (
diff --git a/cf_xarray/tests/test_accessor.py b/cf_xarray/tests/test_accessor.py
index 5fb34bbb..6a57b449 100644
--- a/cf_xarray/tests/test_accessor.py
+++ b/cf_xarray/tests/test_accessor.py
@@ -215,10 +215,13 @@ def test_getitem_ancillary_variables():
 def test_rename_like():
     original = popds.copy(deep=True)
 
-    with pytest.raises(KeyError):
-        popds.cf.rename_like(airds)
+    # it'll match for axis: X (lon, nlon) and coordinate="longitude" (lon, TLONG)
+    # so delete the axis attributes
+    newair = airds.copy(deep=True)
+    del newair.lon.attrs["axis"]
+    del newair.lat.attrs["axis"]
 
-    renamed = popds.cf["TEMP"].cf.rename_like(airds)
+    renamed = popds.cf["TEMP"].cf.rename_like(newair)
     for k in ["TLONG", "TLAT"]:
         assert k not in renamed.coords
         assert k in original.coords
@@ -228,6 +231,20 @@ def test_rename_like():
     assert "lat" in renamed.coords
     assert renamed.attrs["coordinates"] == "lon lat"
 
+    # standard name matching
+    newroms = romsds.expand_dims(latitude=[1], longitude=[1]).cf.guess_coord_axis()
+    renamed = popds.cf["UVEL"].cf.rename_like(newroms)
+    assert renamed.attrs["coordinates"] == "longitude latitude"
+    assert "longitude" in renamed.coords
+    assert "latitude" in renamed.coords
+    assert "ULON" not in renamed.coords
+    assert "ULAT" not in renamed.coords
+
+    # should change "temp" to "TEMP"
+    renamed = romsds.cf.rename_like(popds)
+    assert "temp" not in renamed
+    assert "TEMP" in renamed
+
 
 @pytest.mark.parametrize("obj", objects)
 @pytest.mark.parametrize(

From 2211c97c6ddd2daf916945e44f77be80ed652d97 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Tue, 23 Feb 2021 09:16:42 +0000
Subject: [PATCH 19/22] remove anc

---
 cf_xarray/datasets.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/cf_xarray/datasets.py b/cf_xarray/datasets.py
index 5e6df446..de593471 100644
--- a/cf_xarray/datasets.py
+++ b/cf_xarray/datasets.py
@@ -70,7 +70,6 @@
 anc["q_detection_limit"] = xr.DataArray(
     1e-3, attrs=dict(standard_name="specific_humidity detection_minimum", units="g/g")
 )
-anc
 
 
 multiple = xr.Dataset()

From bc2b14d08a860e30efb3db12891d25f5231a2747 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Tue, 23 Feb 2021 12:03:30 +0000
Subject: [PATCH 20/22] comment out indexes

---
 cf_xarray/accessor.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index f82cfbfa..3b6e7b5d 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -436,7 +436,7 @@ def wrapper(obj: Union[DataArray, Dataset], key: str):
     "labels": (_get_indexes,),  # drop_sel
     "coords": (_get_dims,),  # interp
     "indexers": (_get_dims,),  # sel, isel, reindex
-    "indexes": (_get_dims,),  # set_index TODO: cf_xarray decodes keys, not values
+    #  "indexes": (_single(_get_dims),),  # set_index this decodes keys but not values
     "dims_or_levels": (_get_dims,),  # reset_index
     "window": (_get_dims,),  # rolling_exp
     "coord": (_single(_get_coords),),  # differentiate, integrate

From 29984e7487293bec43032a9a9521b4602f08aa95 Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Tue, 23 Feb 2021 17:20:08 +0000
Subject: [PATCH 21/22] test at least once new functions

---
 cf_xarray/accessor.py            |  2 +-
 cf_xarray/tests/test_accessor.py | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 3b6e7b5d..739fad8e 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -173,7 +173,7 @@ def _apply_single_mapper(mapper):
         try:
             results = mapper(obj, key)
         except KeyError as e:
-            if error:
+            if error or "I expected only one." in repr(e):
                 raise e
             else:
                 results = []
diff --git a/cf_xarray/tests/test_accessor.py b/cf_xarray/tests/test_accessor.py
index 6a57b449..148f6aed 100644
--- a/cf_xarray/tests/test_accessor.py
+++ b/cf_xarray/tests/test_accessor.py
@@ -932,12 +932,33 @@ def test_drop_sel_and_reset_coords(obj):
 
 @pytest.mark.parametrize("ds", datasets)
 def test_drop_dims(ds):
+    # Testing _get_dims
+
+    # Add data_var and coord to test _get_dims
+    ds["lon_var"] = ds["lon"]
+    ds = ds.assign_coords(lon_coord=ds["lon"])
 
     # Axis and coordinate
     for cf_name in ["X", "longitude"]:
         assert_identical(ds.drop_dims("lon"), ds.cf.drop_dims(cf_name))
 
 
+@pytest.mark.parametrize("ds", datasets)
+def test_differentiate(ds):
+    # Testing _single(_get_coords)
+
+    # Add data_var and coord to test _get_dims
+    ds["lon_var"] = ds["lon"]
+    ds = ds.assign_coords(lon_coord=ds["lon"])
+
+    # Axis
+    assert_identical(ds.differentiate("lon"), ds.cf.differentiate("lon"))
+
+    # Multiple keys
+    with pytest.raises(KeyError, match=".*I expected only one."):
+        assert_identical(ds.differentiate("lon"), ds.cf.differentiate("X"))
+
+
 def test_new_standard_name_mappers():
     assert_identical(forecast.cf.mean("realization"), forecast.mean("M"))
     assert_identical(

From 035c8e83c8a0f0379d2a3c494fbb98343917b59d Mon Sep 17 00:00:00 2001
From: malmans2 <mattia.almansi@jhu.edu>
Date: Tue, 23 Feb 2021 17:24:04 +0000
Subject: [PATCH 22/22] fix comments

---
 cf_xarray/tests/test_accessor.py | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/cf_xarray/tests/test_accessor.py b/cf_xarray/tests/test_accessor.py
index 148f6aed..e54e2199 100644
--- a/cf_xarray/tests/test_accessor.py
+++ b/cf_xarray/tests/test_accessor.py
@@ -932,7 +932,6 @@ def test_drop_sel_and_reset_coords(obj):
 
 @pytest.mark.parametrize("ds", datasets)
 def test_drop_dims(ds):
-    # Testing _get_dims
 
     # Add data_var and coord to test _get_dims
     ds["lon_var"] = ds["lon"]
@@ -945,16 +944,15 @@ def test_drop_dims(ds):
 
 @pytest.mark.parametrize("ds", datasets)
 def test_differentiate(ds):
-    # Testing _single(_get_coords)
 
-    # Add data_var and coord to test _get_dims
+    # Add data_var and coord to test _get_coords
     ds["lon_var"] = ds["lon"]
     ds = ds.assign_coords(lon_coord=ds["lon"])
 
-    # Axis
+    # Coordinate
     assert_identical(ds.differentiate("lon"), ds.cf.differentiate("lon"))
 
-    # Multiple keys
+    # Multiple coords (test error raised by _single)
     with pytest.raises(KeyError, match=".*I expected only one."):
         assert_identical(ds.differentiate("lon"), ds.cf.differentiate("X"))