Add python_requires keywords to setup

docs/setuptools.txt

@@ -302,6 +302,10 @@ unless you need the associated ``setuptools`` feature.
     installed to support those features.  See the section below on `Declaring
     Dependencies`_ for details and examples of the format of this argument.
 
+``python_requires``
+    A string corresponding to a version specifier (as defined in PEP 440) for
+    the Python version, used to specify the Requires-Python defined in PEP 345.
+
 ``setup_requires``
     A string or list of strings specifying what other distributions need to
     be present in order for the *setup script* to run.  ``setuptools`` will

setup.py

@@ -95,6 +95,7 @@ def _gen_console_scripts():
             "install_requires       = setuptools.dist:check_requirements",
             "tests_require          = setuptools.dist:check_requirements",
             "setup_requires         = setuptools.dist:check_requirements",
+            "python_requires        = setuptools.dist:check_specifier",
             "entry_points           = setuptools.dist:check_entry_points",
             "test_suite             = setuptools.dist:check_test_suite",
             "zip_safe               = setuptools.dist:assert_bool",

setuptools/dist.py

@@ -39,6 +39,20 @@ def _get_unpatched(cls):
 _Distribution = _get_unpatched(_Distribution)
 
 
+def _patch_distribution_metadata_write_pkg_file():
+    """Patch write_pkg_file to also write Requires-Python/Requires-External"""
+    original_write = distutils.dist.DistributionMetadata.write_pkg_file
+    def write_pkg_file(self, file):
+        """Write the PKG-INFO format data to a file object.
+        """
+        original_write(self, file)
+        if hasattr(self, 'python_requires'):
+            file.write('Requires-Python: %s\n' % self.python_requires)
+
+    distutils.dist.DistributionMetadata.write_pkg_file = write_pkg_file
+_patch_distribution_metadata_write_pkg_file()
+
+
 def _patch_distribution_metadata_write_pkg_info():
     """
     Workaround issue #197 - Python 3 prior to 3.2.2 uses an environment-local
@@ -138,6 +152,18 @@ def check_requirements(dist, attr, value):
         raise DistutilsSetupError(tmpl.format(attr=attr, error=error))
 
 
+def check_specifier(dist, attr, value):
+    """Verify that value is a valid version specifier"""
+    try:
+        packaging.specifiers.SpecifierSet(value)
+    except packaging.specifiers.InvalidSpecifier as error:
+        tmpl = (
+            "{attr!r} must be a string or list of strings "
+            "containing valid version specifiers; {error}"
+        )
+        raise DistutilsSetupError(tmpl.format(attr=attr, error=error))
+
+
 def check_entry_points(dist, attr, value):
     """Verify that entry_points map is parseable"""
     try:
@@ -303,6 +329,8 @@ def __init__(self, attrs=None):
                     "setuptools, pip, and PyPI. Please see PEP 440 for more "
                     "details." % self.metadata.version
                 )
+        if getattr(self, 'python_requires', None):
+            self.metadata.python_requires = self.python_requires
 
     def parse_command_line(self):
         """Process features after parsing command line options"""

setuptools/tests/test_egg_info.py

@@ -210,6 +210,30 @@ def test_extra_requires_with_markers(self, tmpdir_cwd, env):
         self._run_install_command(tmpdir_cwd, env)
         assert glob.glob(os.path.join(env.paths['lib'], 'barbazquux*')) == []
 
+    def test_python_requires_egg_info(self, tmpdir_cwd, env):
+        self._setup_script_with_requires(
+            """python_requires='>=2.7.12',""")
+        environ = os.environ.copy().update(
+            HOME=env.paths['home'],
+        )
+        code, data = environment.run_setup_py(
+            cmd=['egg_info'],
+            pypath=os.pathsep.join([env.paths['lib'], str(tmpdir_cwd)]),
+            data_stream=1,
+            env=environ,
+        )
+        egg_info_dir = os.path.join('.', 'foo.egg-info')
+        pkginfo = os.path.join(egg_info_dir, 'PKG-INFO')
+        assert 'Requires-Python: >=2.7.12' in open(pkginfo).read().split('\n')
+
+    def test_python_requires_install(self, tmpdir_cwd, env):
+        self._setup_script_with_requires(
+            """python_requires='>=1.2.3',""")
+        self._run_install_command(tmpdir_cwd, env)
+        egg_info_dir = self._find_egg_info_files(env.paths['lib']).base
+        pkginfo = os.path.join(egg_info_dir, 'PKG-INFO')
+        assert 'Requires-Python: >=1.2.3' in open(pkginfo).read().split('\n')
+
     def _run_install_command(self, tmpdir_cwd, env, cmd=None, output=None):
         environ = os.environ.copy().update(
             HOME=env.paths['home'],