Move most of the compatibility functionality to _compat

Author: jaraco

importlib_metadata/__init__.py

@@ -6,43 +6,27 @@
 import csv
 import sys
 import zipp
-import email
 import operator
 import functools
 import itertools
 import collections
 
-from ._compat import install, NullFinder
+from ._compat import (
+    install,
+    NullFinder,
+    ConfigParser,
+    suppress,
+    map,
+    FileNotFoundError,
+    NotADirectoryError,
+    pathlib,
+    ModuleNotFoundError,
+    MetaPathFinder,
+    email_message_from_string,
+    )
 from importlib import import_module
 from itertools import starmap
 
-if sys.version_info > (3,):  # pragma: nocover
-    from configparser import ConfigParser
-    from contextlib import suppress
-else:  # pragma: nocover
-    from backports.configparser import ConfigParser
-    from itertools import imap as map  # type: ignore
-    from contextlib2 import suppress  # noqa
-    FileNotFoundError = IOError, OSError
-    NotADirectoryError = IOError, OSError
-
-if sys.version_info > (3, 5):  # pragma: nocover
-    import pathlib
-else:  # pragma: nocover
-    import pathlib2 as pathlib
-
-try:
-    BaseClass = ModuleNotFoundError
-except NameError:                                 # pragma: nocover
-    BaseClass = ImportError                       # type: ignore
-
-
-if sys.version_info >= (3,):  # pragma: nocover
-    from importlib.abc import MetaPathFinder
-else:  # pragma: nocover
-    class MetaPathFinder(object):
-        __metaclass__ = abc.ABCMeta
-
 
 __metaclass__ = type
 
@@ -60,7 +44,7 @@ class MetaPathFinder(object):
     ]
 
 
-class PackageNotFoundError(BaseClass):
+class PackageNotFoundError(ModuleNotFoundError):
     """The package was not found."""
 
 
@@ -232,7 +216,7 @@ def metadata(self):
             # (which points to the egg-info file) attribute unchanged.
             or self.read_text('')
             )
-        return _email_message_from_string(text)
+        return email_message_from_string(text)
 
     @property
     def version(self):
@@ -411,15 +395,6 @@ def locate_file(self, path):
         return self._path.parent / path
 
 
-def _email_message_from_string(text):
-    # Work around https://bugs.python.org/issue25545 where
-    # email.message_from_string cannot handle Unicode on Python 2.
-    if sys.version_info < (3,):                     # nocoverpy3
-        io_buffer = io.StringIO(text)
-        return email.message_from_file(io_buffer)
-    return email.message_from_string(text)          # nocoverpy2
-
-
 def distribution(package):
     """Get the ``Distribution`` instance for the given package.
 

importlib_metadata/_compat.py

@@ -1,7 +1,49 @@
+from __future__ import absolute_import
+
+import io
+import abc
 import sys
+import email
+
+
+if sys.version_info > (3,):  # pragma: nocover
+    import builtins
+    from configparser import ConfigParser
+    from contextlib import suppress
+    FileNotFoundError = builtins.FileNotFoundError
+    NotADirectoryError = builtins.NotADirectoryError
+    map = builtins.map
+else:  # pragma: nocover
+    from backports.configparser import ConfigParser
+    from itertools import imap as map  # type: ignore
+    from contextlib2 import suppress  # noqa
+    FileNotFoundError = IOError, OSError
+    NotADirectoryError = IOError, OSError
+
+if sys.version_info > (3, 5):  # pragma: nocover
+    import pathlib
+else:  # pragma: nocover
+    import pathlib2 as pathlib
+
+try:
+    ModuleNotFoundError = builtins.FileNotFoundError
+except (NameError, AttributeError):  # pragma: nocover
+    ModuleNotFoundError = ImportError  # type: ignore
+
+
+if sys.version_info >= (3,):  # pragma: nocover
+    from importlib.abc import MetaPathFinder
+else:  # pragma: nocover
+    class MetaPathFinder(object):
+        __metaclass__ = abc.ABCMeta
 
 
 __metaclass__ = type
+__all__ = [
+    'install', 'NullFinder', 'MetaPathFinder', 'ModuleNotFoundError',
+    'pathlib', 'ConfigParser', 'map', 'suppress', 'FileNotFoundError',
+    'NotADirectoryError', 'email_message_from_string',
+    ]
 
 
 def install(cls):
@@ -26,3 +68,17 @@ def find_spec(*args, **kwargs):
     # on sys.meta_path but having no other import
     # system functionality), the two methods are identical.
     find_module = find_spec
+
+
+def py2_message_from_string(text):
+    # Work around https://bugs.python.org/issue25545 where
+    # email.message_from_string cannot handle Unicode on Python 2.
+    io_buffer = io.StringIO(text)
+    return email.message_from_file(io_buffer)
+
+
+email_message_from_string = (
+    py2_message_from_string
+    if sys.version_info < (3,) else
+    email.message_from_string
+    )