Update pip-download to respect --python-version.

7 files changed, 126 insertions, 43 deletions

diff --git a/news/5369.bugfix b/news/5369.bugfix
new file mode 100644
index 000000000..e17f88289
--- /dev/null
+++ b/news/5369.bugfix
@@ -0,0 +1,2 @@
+Update ``pip download`` to respect the given ``--python-version`` when checking
+``"Requires-Python"``.
diff --git a/src/pip/_internal/commands/download.py b/src/pip/_internal/commands/download.py
index b2c9ce49e..abdd1c2d0 100644
--- a/src/pip/_internal/commands/download.py
+++ b/src/pip/_internal/commands/download.py
@@ -152,6 +152,7 @@ class DownloadCommand(RequirementCommand):
                     upgrade_strategy="to-satisfy-only",
                     force_reinstall=False,
                     ignore_dependencies=options.ignore_dependencies,
+                    py_version_info=options.python_version,
                     ignore_requires_python=False,
                     ignore_installed=True,
                     isolated=options.isolated_mode,
diff --git a/src/pip/_internal/index.py b/src/pip/_internal/index.py
index d6e30a483..16ace1a45 100644
--- a/src/pip/_internal/index.py
+++ b/src/pip/_internal/index.py
@@ -34,7 +34,7 @@ from pip._internal.utils.compat import ipaddress
 from pip._internal.utils.logging import indent_log
 from pip._internal.utils.misc import (
     ARCHIVE_EXTENSIONS, SUPPORTED_EXTENSIONS, WHEEL_EXTENSION, normalize_path,
-    path_to_url, redact_password_from_url,
+    normalize_version_info, path_to_url, redact_password_from_url,
 )
 from pip._internal.utils.packaging import check_requires_python
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
@@ -258,7 +258,7 @@ def _get_html_page(link, session=None):
 
 def _check_link_requires_python(
     link,  # type: Link
-    version_info,  # type: Tuple[int, ...]
+    version_info,  # type: Tuple[int, int, int]
     ignore_requires_python=False,  # type: bool
 ):
     # type: (...) -> bool
@@ -266,8 +266,8 @@ def _check_link_requires_python(
     Return whether the given Python version is compatible with a link's
     "Requires-Python" value.
 
-    :param version_info: The Python version to use to check, as a 3-tuple
-        of ints (major-minor-micro).
+    :param version_info: A 3-tuple of ints representing the Python
+        major-minor-micro version to check.
     :param ignore_requires_python: Whether to ignore the "Requires-Python"
         value if the given Python version isn't compatible.
     """
@@ -311,16 +311,17 @@ class CandidateEvaluator(object):
         valid_tags,          # type: List[Pep425Tag]
         prefer_binary=False,   # type: bool
         allow_all_prereleases=False,  # type: bool
-        py_version_info=None,  # type: Optional[Tuple[int, ...]]
+        py_version_info=None,  # type: Optional[Tuple[int, int, int]]
         ignore_requires_python=None,  # type: Optional[bool]
     ):
         # type: (...) -> None
         """
         :param allow_all_prereleases: Whether to allow all pre-releases.
-        :param py_version_info: The Python version, as a 3-tuple of ints
-            representing a major-minor-micro version, to use to check both
-            the Python version embedded in the filename and the package's
-            "Requires-Python" metadata. Defaults to `sys.version_info[:3]`.
+        :param py_version_info: A 3-tuple of ints representing the Python
+            major-minor-micro version to use to check both the Python version
+            embedded in the filename and the package's "Requires-Python"
+            metadata. If None (the default), then `sys.version_info[:3]`
+            will be used.
         :param ignore_requires_python: Whether to ignore incompatible
             "Requires-Python" values in links. Defaults to False.
         """
@@ -666,6 +667,8 @@ class PackageFinder(object):
         else:
             versions = None
 
+        py_version_info = normalize_version_info(py_version_info)
+
         # The valid tags to check potential found wheel candidates against
         valid_tags = get_supported(
             versions=versions,
@@ -676,6 +679,7 @@ class PackageFinder(object):
         candidate_evaluator = CandidateEvaluator(
             valid_tags=valid_tags, prefer_binary=prefer_binary,
             allow_all_prereleases=allow_all_prereleases,
+            py_version_info=py_version_info,
             ignore_requires_python=ignore_requires_python,
         )
 
diff --git a/src/pip/_internal/legacy_resolve.py b/src/pip/_internal/legacy_resolve.py
index a6714cb1f..1cc8531d1 100644
--- a/src/pip/_internal/legacy_resolve.py
+++ b/src/pip/_internal/legacy_resolve.py
@@ -23,7 +23,9 @@ from pip._internal.exceptions import (
 )
 from pip._internal.req.constructors import install_req_from_req_string
 from pip._internal.utils.logging import indent_log
-from pip._internal.utils.misc import dist_in_usersite, ensure_dir
+from pip._internal.utils.misc import (
+    dist_in_usersite, ensure_dir, normalize_version_info,
+)
 from pip._internal.utils.packaging import (
     check_requires_python, get_requires_python,
 )
@@ -46,7 +48,7 @@ logger = logging.getLogger(__name__)
 
 def _check_dist_requires_python(
     dist,  # type: pkg_resources.Distribution
-    version_info,  # type: Tuple[int, ...]
+    version_info,  # type: Tuple[int, int, int]
     ignore_requires_python=False,  # type: bool
 ):
     # type: (...) -> None
@@ -54,8 +56,8 @@ def _check_dist_requires_python(
     Check whether the given Python version is compatible with a distribution's
     "Requires-Python" value.
 
-    :param version_info: The Python version to use to check, as a 3-tuple
-        of ints (major-minor-micro).
+    :param version_info: A 3-tuple of ints representing the Python
+        major-minor-micro version to check.
     :param ignore_requires_python: Whether to ignore the "Requires-Python"
         value if the given Python version isn't compatible.
 
@@ -121,6 +123,8 @@ class Resolver(object):
 
         if py_version_info is None:
             py_version_info = sys.version_info[:3]
+        else:
+            py_version_info = normalize_version_info(py_version_info)
 
         self._py_version_info = py_version_info
 
diff --git a/src/pip/_internal/utils/packaging.py b/src/pip/_internal/utils/packaging.py
index 2d80920df..68aa86edb 100644
--- a/src/pip/_internal/utils/packaging.py
+++ b/src/pip/_internal/utils/packaging.py
@@ -22,16 +22,15 @@ logger = logging.getLogger(__name__)
 def check_requires_python(requires_python, version_info):
     # type: (Optional[str], Tuple[int, ...]) -> bool
     """
-    Check if the given Python version matches a `requires_python` specifier.
+    Check if the given Python version matches a "Requires-Python" specifier.
 
-    :param version_info: A 3-tuple of ints representing the Python
+    :param version_info: A 3-tuple of ints representing a Python
         major-minor-micro version to check (e.g. `sys.version_info[:3]`).
 
-    Returns `True` if the version of python in use matches the requirement.
-    Returns `False` if the version of python in use does not matches the
-    requirement.
+    :return: `True` if the given Python version satisfies the requirement.
+        Otherwise, return `False`.
 
-    Raises an InvalidSpecifier if `requires_python` have an invalid format.
+    :raises InvalidSpecifier: If `requires_python` has an invalid format.
     """
     if requires_python is None:
         # The package provides no information
diff --git a/tests/functional/test_download.py b/tests/functional/test_download.py
index e318aa004..b216450db 100644
--- a/tests/functional/test_download.py
+++ b/tests/functional/test_download.py
@@ -1,3 +1,4 @@
+import os.path
 import textwrap
 
 import pytest
@@ -388,7 +389,7 @@ class TestDownloadPlatformManylinuxes(object):
         )
 
 
-def test_download_specify_python_version(script, data):
+def test_download__python_version(script, data):
     """
     Test using "pip download --python-version" to download a .whl archive
     supported for a specific interpreter
@@ -477,6 +478,63 @@ def test_download_specify_python_version(script, data):
     )
 
 
+def make_wheel_with_python_requires(script, package_name, python_requires):
+    """
+    Create a wheel using the given python_requires.
+
+    :return: the path to the wheel file.
+    """
+    package_dir = script.scratch_path / package_name
+    package_dir.mkdir()
+
+    text = textwrap.dedent("""\
+    from setuptools import setup
+    setup(name='{}',
+          python_requires='{}',
+          version='1.0')
+    """).format(package_name, python_requires)
+    package_dir.join('setup.py').write(text)
+    script.run(
+        'python', 'setup.py', 'bdist_wheel', '--universal', cwd=package_dir,
+    )
+
+    file_name = '{}-1.0-py2.py3-none-any.whl'.format(package_name)
+    return package_dir / 'dist' / file_name
+
+
+def test_download__python_version_used_for_python_requires(
+    script, data, with_wheel,
+):
+    """
+    Test that --python-version is used for the Requires-Python check.
+    """
+    wheel_path = make_wheel_with_python_requires(
+        script, 'mypackage', python_requires='==3.2',
+    )
+    wheel_dir = os.path.dirname(wheel_path)
+
+    def make_args(python_version):
+        return [
+            'download', '--no-index', '--find-links', wheel_dir,
+            '--only-binary=:all:',
+            '--dest', '.',
+            '--python-version', python_version,
+            'mypackage==1.0',
+        ]
+
+    args = make_args('33')
+    result = script.pip(*args, expect_error=True)
+    expected_err = (
+        "ERROR: Package 'mypackage' requires a different Python: "
+        "3.3.0 not in '==3.2'"
+    )
+    assert expected_err in result.stderr, 'stderr: {}'.format(result.stderr)
+
+    # Now try with a --python-version that satisfies the Requires-Python.
+    args = make_args('32')
+    script.pip(*args)  # no exception
+
+
 def test_download_specify_abi(script, data):
     """
     Test using "pip download --abi" to download a .whl archive
diff --git a/tests/unit/test_index.py b/tests/unit/test_index.py
index 513826d61..1d6c48040 100644
--- a/tests/unit/test_index.py
+++ b/tests/unit/test_index.py
@@ -13,6 +13,8 @@ from pip._internal.index import (
     _egg_info_matches, _find_name_version_sep, _get_html_page,
 )
 
+CURRENT_PY_VERSION_INFO = sys.version_info[:3]
+
 
 @pytest.mark.parametrize('requires_python, expected', [
     ('== 3.6.4', False),
@@ -82,27 +84,33 @@ def test_check_link_requires_python__invalid_requires(caplog):
 
 class TestCandidateEvaluator:
 
-    @pytest.mark.parametrize("version_info, expected", [
+    @pytest.mark.parametrize('py_version_info, expected_py_version', [
         ((2, 7, 14), '2.7'),
         ((3, 6, 5), '3.6'),
         # Check a minor version with two digits.
         ((3, 10, 1), '3.10'),
     ])
-    def test_init__py_version(self, version_info, expected):
+    def test_init__py_version_info(self, py_version_info, expected_py_version):
         """
-        Test the _py_version attribute.
+        Test the py_version_info argument.
         """
-        evaluator = CandidateEvaluator([], py_version_info=version_info)
-        assert evaluator._py_version == expected
+        evaluator = CandidateEvaluator([], py_version_info=py_version_info)
+
+        # The _py_version_info attribute should be set as is.
+        assert evaluator._py_version_info == py_version_info
+        assert evaluator._py_version == expected_py_version
 
-    def test_init__py_version_default(self):
+    def test_init__py_version_info_none(self):
         """
-        Test the _py_version attribute's default value.
+        Test passing None for the py_version_info argument.
         """
-        evaluator = CandidateEvaluator([])
+        evaluator = CandidateEvaluator([], py_version_info=None)
         # Get the index of the second dot.
         index = sys.version.find('.', 2)
-        assert evaluator._py_version == sys.version[:index]
+        current_major_minor = sys.version[:index]  # e.g. "3.6"
+
+        assert evaluator._py_version_info == CURRENT_PY_VERSION_INFO
+        assert evaluator._py_version == current_major_minor
 
     @pytest.mark.parametrize(
         'py_version_info,ignore_requires_python,expected', [
@@ -151,30 +159,37 @@ class TestCandidateEvaluator:
 
 class TestPackageFinder:
 
-    @pytest.mark.parametrize('version_info, expected', [
-        ((2,), ['2']),
-        ((3,), ['3']),
-        ((3, 6,), ['36']),
-        # Test a tuple of length 3.
-        ((3, 6, 5), ['36']),
+    @pytest.mark.parametrize('py_version_info, expected', [
+        # Test tuples of varying lengths.
+        ((), (None, (0, 0, 0))),
+        ((2, ), (['2'], (2, 0, 0))),
+        ((3, ), (['3'], (3, 0, 0))),
+        ((3, 6,), (['36'], (3, 6, 0))),
+        ((3, 6, 5), (['36'], (3, 6, 5))),
         # Test a 2-digit minor version.
-        ((3, 10), ['310']),
-        # Test falsey values.
-        (None, None),
-        ((), None),
+        ((3, 10), (['310'], (3, 10, 0))),
+        # Test passing None.
+        (None, (None, CURRENT_PY_VERSION_INFO)),
     ])
     @patch('pip._internal.index.get_supported')
     def test_create__py_version_info(
-        self, mock_get_supported, version_info, expected,
+        self, mock_get_supported, py_version_info, expected,
     ):
         """
         Test that the py_version_info argument is handled correctly.
         """
-        PackageFinder.create(
-            [], [], py_version_info=version_info, session=object(),
+        expected_versions, expected_evaluator_info = expected
+        finder = PackageFinder.create(
+            [], [], py_version_info=py_version_info, session=object(),
         )
         actual = mock_get_supported.call_args[1]['versions']
-        assert actual == expected
+        assert actual == expected_versions
+
+        # For candidate_evaluator, we only need to test _py_version_info
+        # since setting _py_version correctly is tested in
+        # TestCandidateEvaluator.
+        evaluator = finder.candidate_evaluator
+        assert evaluator._py_version_info == expected_evaluator_info
 
 
 def test_sort_locations_file_expand_dir(data):