Mention packaging on pkg_resources deprecation notes (#3949)

Author: abravalheri

docs/pkg_resources.rst

@@ -14,6 +14,8 @@ packages.
    Use of ``pkg_resources`` is deprecated in favor of
    :mod:`importlib.resources`, :mod:`importlib.metadata`
    and their backports (:pypi:`importlib_resources`, :pypi:`importlib_metadata`).
+   Some useful APIs are also provided by :pypi:`packaging` (e.g. requirements
+   and version parsing).
    Users should refrain from new usage of ``pkg_resources`` and
    should work to port to importlib-based solutions.
 

pkg_resources/__init__.py

@@ -13,11 +13,8 @@
 .zip files and with custom PEP 302 loaders that support the ``get_data()``
 method.
 
-This module is deprecated. Users are directed to
-`importlib.resources <https://docs.python.org/3/library/importlib.resources.html>`_
-and
-`importlib.metadata <https://docs.python.org/3/library/importlib.metadata.html>`_
-instead.
+This module is deprecated. Users are directed to :mod:`importlib.resources`,
+:mod:`importlib.metadata` and :pypi:`packaging` instead.
 """
 
 import sys
@@ -118,9 +115,12 @@
 _namespace_packages = None
 
 
-warnings.warn("pkg_resources is deprecated as an API.  "
-              "See https://setuptools.pypa.io/en/latest/pkg_resources.html",
-              DeprecationWarning, stacklevel=2)
+warnings.warn(
+    "pkg_resources is deprecated as an API. "
+    "See https://setuptools.pypa.io/en/latest/pkg_resources.html",
+    DeprecationWarning,
+    stacklevel=2
+)
 
 
 _PEP440_FALLBACK = re.compile(r"^v?(?P<safe>(?:[0-9]+!)?[0-9]+(?:\.[0-9]+)*)", re.I)