Added --prefer-binary flag.

news/3785.feature

@@ -0,0 +1 @@
+Introduce a new --prefer-binary flag, to prefer older wheels over newer source packages.

src/pip/_internal/basecommand.py

@@ -370,4 +370,5 @@ def _build_package_finder(self, options, session,
             versions=python_versions,
             abi=abi,
             implementation=implementation,
+            prefer_binary=options.prefer_binary,
         )

src/pip/_internal/cmdoptions.py

@@ -406,6 +406,16 @@ def only_binary():
     )
 
 
+def prefer_binary():
+    return Option(
+        "--prefer-binary",
+        dest="prefer_binary",
+        action="store_true",
+        default=False,
+        help="Prefer older binary packages over newer source packages."
+    )
+
+
 cache_dir = partial(
     Option,
     "--cache-dir",

src/pip/_internal/commands/download.py

@@ -52,6 +52,7 @@ def __init__(self, *args, **kw):
         cmd_opts.add_option(cmdoptions.global_options())
         cmd_opts.add_option(cmdoptions.no_binary())
         cmd_opts.add_option(cmdoptions.only_binary())
+        cmd_opts.add_option(cmdoptions.prefer_binary())
         cmd_opts.add_option(cmdoptions.src())
         cmd_opts.add_option(cmdoptions.pre())
         cmd_opts.add_option(cmdoptions.no_clean())

src/pip/_internal/commands/install.py

@@ -183,6 +183,7 @@ def __init__(self, *args, **kw):
 
         cmd_opts.add_option(cmdoptions.no_binary())
         cmd_opts.add_option(cmdoptions.only_binary())
+        cmd_opts.add_option(cmdoptions.prefer_binary())
         cmd_opts.add_option(cmdoptions.no_clean())
         cmd_opts.add_option(cmdoptions.require_hashes())
         cmd_opts.add_option(cmdoptions.progress_bar())

src/pip/_internal/commands/wheel.py

@@ -57,6 +57,7 @@ def __init__(self, *args, **kw):
         )
         cmd_opts.add_option(cmdoptions.no_binary())
         cmd_opts.add_option(cmdoptions.only_binary())
+        cmd_opts.add_option(cmdoptions.prefer_binary())
         cmd_opts.add_option(
             '--build-option',
             dest='build_options',

src/pip/_internal/index.py

@@ -108,7 +108,8 @@ class PackageFinder(object):
     def __init__(self, find_links, index_urls, allow_all_prereleases=False,
                  trusted_hosts=None, process_dependency_links=False,
                  session=None, format_control=None, platform=None,
-                 versions=None, abi=None, implementation=None):
+                 versions=None, abi=None, implementation=None,
+                 prefer_binary=False):
         """Create a PackageFinder.
 
         :param format_control: A FormatControl object or None. Used to control
@@ -176,6 +177,9 @@ def __init__(self, find_links, index_urls, allow_all_prereleases=False,
             impl=implementation,
         )
 
+        # Do we prefer old, but valid, binary dist over new source dist
+        self.prefer_binary = prefer_binary
+
         # If we don't have TLS enabled, then WARN if anyplace we're looking
         # relies on TLS.
         if not HAS_TLS:
@@ -275,12 +279,14 @@ def _candidate_sort_key(self, candidate):
           1. existing installs
           2. wheels ordered via Wheel.support_index_min(self.valid_tags)
           3. source archives
+        If prefer_binary was set, then all wheels are sorted above sources.
         Note: it was considered to embed this logic into the Link
               comparison operators, but then different sdist links
               with the same version, would have to be considered equal
         """
         support_num = len(self.valid_tags)
         build_tag = tuple()
+        binary_preference = 0
         if candidate.location.is_wheel:
             # can raise InvalidWheelFilename
             wheel = Wheel(candidate.location.filename)
@@ -289,14 +295,16 @@ def _candidate_sort_key(self, candidate):
                     "%s is not a supported wheel for this platform. It "
                     "can't be sorted." % wheel.filename
                 )
+            if self.prefer_binary:
+                binary_preference = 1
             pri = -(wheel.support_index_min(self.valid_tags))
             if wheel.build_tag is not None:
                 match = re.match(r'^(\d+)(.*)$', wheel.build_tag)
                 build_tag_groups = match.groups()
                 build_tag = (int(build_tag_groups[0]), build_tag_groups[1])
         else:  # sdist
             pri = -(support_num)
-        return (candidate.version, build_tag, pri)
+        return (binary_preference, candidate.version, build_tag, pri)
 
     def _validate_secure_origin(self, logger, location):
         # Determine if this url used a secure transport mechanism

tests/functional/test_download.py

@@ -602,3 +602,60 @@ def test_download_exit_status_code_when_blank_requirements_file(script):
     """
     script.scratch_path.join("blank.txt").write("\n")
     script.pip('download', '-r', 'blank.txt')
+
+
+def test_download_prefer_binary_when_tarball_higher_than_wheel(script, data):
+    fake_wheel(data, 'source-0.8-py2.py3-none-any.whl')
+    result = script.pip(
+        'download',
+        '--prefer-binary',
+        '--no-index',
+        '-f', data.packages,
+        '-d', '.', 'source'
+    )
+    assert (
+        Path('scratch') / 'source-0.8-py2.py3-none-any.whl'
+        in result.files_created
+    )
+    assert (
+        Path('scratch') / 'source-1.0.tar.gz'
+        not in result.files_created
+    )
+
+
+def test_download_prefer_binary_when_wheel_doesnt_satisfy_req(script, data):
+    fake_wheel(data, 'source-0.8-py2.py3-none-any.whl')
+    script.scratch_path.join("test-req.txt").write(textwrap.dedent("""
+        source>0.9
+        """))
+
+    result = script.pip(
+        'download',
+        '--prefer-binary',
+        '--no-index',
+        '-f', data.packages,
+        '-d', '.',
+        '-r', script.scratch_path / 'test-req.txt'
+    )
+    assert (
+        Path('scratch') / 'source-1.0.tar.gz'
+        in result.files_created
+    )
+    assert (
+        Path('scratch') / 'source-0.8-py2.py3-none-any.whl'
+        not in result.files_created
+    )
+
+
+def test_download_prefer_binary_when_only_tarball_exists(script, data):
+    result = script.pip(
+        'download',
+        '--prefer-binary',
+        '--no-index',
+        '-f', data.packages,
+        '-d', '.', 'source'
+    )
+    assert (
+        Path('scratch') / 'source-1.0.tar.gz'
+        in result.files_created
+    )