Add a platform-dependent self-check that runs during `import tensorfl…

…ow`.

This gives us the opportunity to raise actionable error messages (e.g. about
missing DLLs on Windows) that are more useful than the loader errors we get
from a failed SWIG import.

PiperOrigin-RevId: 169315291

tensorflow/python/platform/self_check.py

@@ -0,0 +1,49 @@
+# Copyright 2017 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+
+"""Platform-specific code for checking the integrity of the TensorFlow build."""
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import os
+
+
+def preload_check():
+  """Raises an exception if the environment is not correctly configured.
+
+  Raises:
+    ImportError: If the check detects that the environment is not correctly
+      configured, and attempting to load the TensorFlow runtime will fail.
+  """
+  if os.name == "nt":
+    # Attempt to load any DLLs that the Python extension depends on before
+    # we load the Python extension, so that we can raise an actionable error
+    # message if they are not found.
+    import ctypes  # pylint: disable=g-import-not-at-top
+    try:
+      ctypes.WinDLL("msvcp140.dll")
+    except OSError:
+      raise ImportError(
+          "Could not find 'msvcp140.dll'. TensorFlow requires that this DLL be "
+          "installed in a directory that is named in your %PATH% environment "
+          "variable. You may install this DLL by downloading Visual C++ 2015 "
+          "Redistributable Update 3 from this URL: "
+          "https://www.microsoft.com/en-us/download/details.aspx?id=53587")
+    # TODO(mrry): Add specific checks for GPU DLLs if build_info indicates
+    # that this is a GPU build.
+  else:
+    # TODO(mrry): Consider adding checks for the Linux and Mac OS X builds.
+    pass

tensorflow/python/pywrap_tensorflow.py

@@ -22,6 +22,13 @@
 import sys
 import traceback
 
+from tensorflow.python.platform import self_check
+
+
+# Perform pre-load sanity checks in order to produce a more actionable error
+# than we get from an error during SWIG import.
+self_check.preload_check()
+
 # pylint: disable=wildcard-import,g-import-not-at-top,unused-import,line-too-long
 
 # On UNIX-based platforms, pywrap_tensorflow is a SWIG-generated