Better user experience when the version of TF is not right. (tensorflow#1281)

* Better user experience when the version of TF is not right.

Author: gabrieldemarmiesse

tensorflow_addons/utils/ensure_tf_install.py

@@ -17,27 +17,40 @@
 # Ensure TensorFlow is importable and its version is sufficiently recent. This
 # needs to happen before anything else, since the imports below will try to
 # import tensorflow, too.
+
+from distutils.version import LooseVersion
+import warnings
+
+import tensorflow as tf
+
+
+warning_template = """
+This version of TensorFlow Addons requires TensorFlow {required}.
+Detected an installation of version {present}.
+
+While some functions might work, TensorFlow Addons was not tested
+with this TensorFlow version. Also custom ops were not compiled
+against this version of TensorFlow. If you use custom ops,
+you might get errors (segmentation faults for example).
+
+It might help you to fallback to pure Python ops with
+TF_ADDONS_PY_OPS . To do that, see
+https://github.com/tensorflow/addons#gpucpu-custom-ops
+
+If you encounter errors, do *not* file bugs in GitHub because
+the version of TensorFlow you are using is not supported.
+"""
+
+
 def _ensure_tf_install():
-    """Attempt to import tensorflow, and ensure its version is sufficient.
-    Raises:
-      ImportError: if either tensorflow is not importable or its version is
-      inadequate.
+    """Warn the user if the version of TensorFlow used is not supported.
     """
-    import tensorflow as tf
-    import distutils.version
 
-    #
     # Update this whenever we need to depend on a newer TensorFlow release.
-    #
-    required_tensorflow_version = "2.1.0"
-
-    if distutils.version.LooseVersion(tf.__version__) < distutils.version.LooseVersion(
-        required_tensorflow_version
-    ):
-        raise ImportError(
-            "This version of TensorFlow Addons requires TensorFlow "
-            "version >= {required}; Detected an installation of version "
-            "{present}. Please upgrade TensorFlow to proceed.".format(
-                required=required_tensorflow_version, present=tf.__version__
-            )
+    required_tf_version = "2.1.0"
+
+    if LooseVersion(tf.__version__) != LooseVersion(required_tf_version):
+        message = warning_template.format(
+            required=required_tf_version, present=tf.__version__
         )
+        warnings.warn(message, UserWarning)