Add --ignore-requires-python escape hatch

CHANGES.txt

@@ -53,6 +53,7 @@
 * Normalize package names before using in ``pip show`` (:issue:`3976`)
 
 * Raises when Requires-Python do not match the running version.
+  Add ``--ignore-requires-python`` escape hatch.
 
 
 **8.1.2 (2016-05-10)**

pip/cmdoptions.py

@@ -477,6 +477,13 @@ def only_binary():
     help='Directory to unpack packages into and build in.'
 )
 
+ignore_requires_python = partial(
+    Option,
+    '--ignore-requires-python',
+    dest='ignore_requires_python',
+    action='store_true',
+    help='Ignore the Requires-Python information.')
+
 install_options = partial(
     Option,
     '--install-option',

pip/commands/install.py

@@ -118,6 +118,7 @@ def __init__(self, *args, **kw):
             action='store_true',
             help='Ignore the installed packages (reinstalling instead).')
 
+        cmd_opts.add_option(cmdoptions.ignore_requires_python())
         cmd_opts.add_option(cmdoptions.no_deps())
 
         cmd_opts.add_option(cmdoptions.install_options())
@@ -295,6 +296,7 @@ def run(self, options, args):
                     as_egg=options.as_egg,
                     ignore_installed=options.ignore_installed,
                     ignore_dependencies=options.ignore_dependencies,
+                    ignore_requires_python=options.ignore_requires_python,
                     force_reinstall=options.force_reinstall,
                     use_user_site=options.use_user_site,
                     target_dir=temp_target_dir,

pip/commands/wheel.py

@@ -70,6 +70,7 @@ def __init__(self, *args, **kw):
         cmd_opts.add_option(cmdoptions.editable())
         cmd_opts.add_option(cmdoptions.requirements())
         cmd_opts.add_option(cmdoptions.src())
+        cmd_opts.add_option(cmdoptions.ignore_requires_python())
         cmd_opts.add_option(cmdoptions.no_deps())
         cmd_opts.add_option(cmdoptions.build_dir())
 
@@ -171,6 +172,7 @@ def run(self, options, args):
                     download_dir=None,
                     ignore_dependencies=options.ignore_dependencies,
                     ignore_installed=True,
+                    ignore_requires_python=options.ignore_requires_python,
                     isolated=options.isolated_mode,
                     session=session,
                     wheel_cache=wheel_cache,

pip/req/req_set.py

@@ -14,7 +14,8 @@
 from pip.exceptions import (InstallationError, BestVersionAlreadyInstalled,
                             DistributionNotFound, PreviousBuildDirError,
                             HashError, HashErrors, HashUnpinned,
-                            DirectoryUrlHashUnsupported, VcsHashUnsupported)
+                            DirectoryUrlHashUnsupported, VcsHashUnsupported,
+                            UnsupportedPythonVersion)
 from pip.req.req_install import InstallRequirement
 from pip.utils import (
     display_path, dist_in_usersite, ensure_dir, normalize_path)
@@ -145,7 +146,8 @@ def __init__(self, build_dir, src_dir, download_dir, upgrade=False,
                  target_dir=None, ignore_dependencies=False,
                  force_reinstall=False, use_user_site=False, session=None,
                  pycompile=True, isolated=False, wheel_download_dir=None,
-                 wheel_cache=None, require_hashes=False):
+                 wheel_cache=None, require_hashes=False,
+                 ignore_requires_python=False):
         """Create a RequirementSet.
 
         :param wheel_download_dir: Where still-packed .whl files should be
@@ -179,6 +181,7 @@ def __init__(self, build_dir, src_dir, download_dir, upgrade=False,
         self.requirement_aliases = {}
         self.unnamed_requirements = []
         self.ignore_dependencies = ignore_dependencies
+        self.ignore_requires_python = ignore_requires_python
         self.successfully_downloaded = []
         self.successfully_installed = []
         self.reqs_to_cleanup = []
@@ -656,7 +659,13 @@ def _prepare_file(self,
             # # parse dependencies # #
             # ###################### #
             dist = abstract_dist.dist(finder)
-            check_dist_requires_python(dist)
+            try:
+                check_dist_requires_python(dist)
+            except UnsupportedPythonVersion as e:
+                if self.ignore_requires_python:
+                    logger.warning(e.args[0])
+                else:
+                    raise
             more_reqs = []
 
             def add_req(subreq):