Add basic tests and docs for python_requires

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

setuptools/tests/test_egg_info.py

@@ -210,6 +210,30 @@ class TestEggInfo(object):
         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'],