Fix import errors and extend module docs

Author: timhoffm

lib/matplotlib/_api/__init__.py

@@ -1,9 +1,12 @@
 """
 Helper functions for managing the Matplotlib API.
 
+This documentation is only relevant for Matplotlib developers, not for users.
+
 .. warning:
 
-    This module and its submodules is for internal use only.
+    This module and its submodules are for internal use only.  Do not use them
+    in your own code.  We may change the API at any time with no warning.
 
 """
 

lib/matplotlib/_api/deprecation.py

@@ -1,3 +1,15 @@
+"""
+Helper functions for deprecating parts of the Matplotlib API.
+
+This documentation is only relevant for Matplotlib developers, not for users.
+
+.. warning:
+
+    This module is for internal use only.  Do not use it in your own code.
+    We may change the API at any time with no warning.
+
+"""
+
 import contextlib
 import functools
 import inspect

lib/matplotlib/patches.py

@@ -9,7 +9,7 @@
 import numpy as np
 
 import matplotlib as mpl
-from . import (artist, cbook, colors, docstring, hatch as mhatch,
+from . import (_api, artist, cbook, colors, docstring, hatch as mhatch,
                lines as mlines, transforms)
 from .bezier import (
     NonIntersectingPathException, get_cos_sin, get_intersection,
@@ -2007,8 +2007,8 @@ def __init_subclass__(cls):
             @cbook._delete_parameter("3.4", "mutation_aspect")
             def call_wrapper(
                     self, x0, y0, width, height, mutation_size,
-                    mutation_aspect=cbook.deprecation._deprecated_parameter):
-                if mutation_aspect is cbook.deprecation._deprecated_parameter:
+                    mutation_aspect=_api.deprecation._deprecated_parameter):
+                if mutation_aspect is _api.deprecation._deprecated_parameter:
                     # Don't trigger deprecation warning internally.
                     return __call__(self, x0, y0, width, height, mutation_size)
                 else: