[python] Make the collections import future-proof

On Python 3.7 the old code raises a warning:

	DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working
    	class ArgumentsIterator(collections.Sequence):

On Python 3.8 it wouldn't work anymore.

Commited on behalf of Jakub Stasiak.

Differential Revision: https://reviews.llvm.org/D56341

llvm-svn: 350467

clang/bindings/python/clang/cindex.py

@@ -64,7 +64,6 @@ from __future__ import absolute_import, division, print_function
 # o implement additional SourceLocation, SourceRange, and File methods.
 
 from ctypes import *
-import collections
 
 import clang.enumerations
 
@@ -123,6 +122,14 @@ elif sys.version_info[0] == 2:
     def b(x):
         return x
 
+# Importing ABC-s directly from collections is deprecated since Python 3.7,
+# will stop working in Python 3.8.
+# See: https://docs.python.org/dev/whatsnew/3.7.html#id3
+if sys.version_info[:2] >= (3, 7):
+    from collections import abc as collections_abc
+else:
+    import collections as collections_abc
+
 # We only support PathLike objects on Python version with os.fspath present
 # to be consistent with the Python standard library. On older Python versions
 # we only support strings and we have dummy fspath to just pass them through.
@@ -2181,7 +2188,7 @@ class Type(Structure):
         The returned object is iterable and indexable. Each item in the
         container is a Type instance.
         """
-        class ArgumentsIterator(collections.Sequence):
+        class ArgumentsIterator(collections_abc.Sequence):
             def __init__(self, parent):
                 self.parent = parent
                 self.length = None