Move lru_cache shim to utils.compat

src/pip/_internal/index/collector.py

@@ -21,6 +21,7 @@
 from pip._internal.models.link import Link
 from pip._internal.models.search_scope import SearchScope
 from pip._internal.network.utils import raise_for_status
+from pip._internal.utils.compat import lru_cache
 from pip._internal.utils.filetypes import ARCHIVE_EXTENSIONS
 from pip._internal.utils.misc import pairwise, redact_auth_from_url
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
@@ -31,7 +32,7 @@
     from optparse import Values
     from typing import (
         Callable, Iterable, List, MutableMapping, Optional,
-        Protocol, Sequence, Tuple, TypeVar, Union,
+        Sequence, Tuple, Union,
     )
     import xml.etree.ElementTree
 
@@ -42,31 +43,10 @@
     HTMLElement = xml.etree.ElementTree.Element
     ResponseHeaders = MutableMapping[str, str]
 
-    # Used in the @lru_cache polyfill.
-    F = TypeVar('F')
-
-    class LruCache(Protocol):
-        def __call__(self, maxsize=None):
-            # type: (Optional[int]) -> Callable[[F], F]
-            raise NotImplementedError
-
 
 logger = logging.getLogger(__name__)
 
 
-# Fallback to noop_lru_cache in Python 2
-# TODO: this can be removed when python 2 support is dropped!
-def noop_lru_cache(maxsize=None):
-    # type: (Optional[int]) -> Callable[[F], F]
-    def _wrapper(f):
-        # type: (F) -> F
-        return f
-    return _wrapper
-
-
-_lru_cache = getattr(functools, "lru_cache", noop_lru_cache)  # type: LruCache
-
-
 def _match_vcs_scheme(url):
     # type: (str) -> Optional[str]
     """Look for VCS schemes in the URL.
@@ -336,7 +316,7 @@ def with_cached_html_pages(
     `page` has `page.cache_link_parsing == False`.
     """
 
-    @_lru_cache(maxsize=None)
+    @lru_cache(maxsize=None)
     def wrapper(cacheable_page):
         # type: (CacheablePageContent) -> List[Link]
         return list(fn(cacheable_page.page))

src/pip/_internal/utils/compat.py

@@ -7,6 +7,7 @@
 from __future__ import absolute_import, division
 
 import codecs
+import functools
 import locale
 import logging
 import os
@@ -18,7 +19,17 @@
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
 
 if MYPY_CHECK_RUNNING:
-    from typing import Optional, Text, Tuple, Union
+    from typing import (
+        Callable, Optional, Protocol, Text, Tuple, TypeVar, Union,
+    )
+
+    # Used in the @lru_cache polyfill.
+    F = TypeVar('F')
+
+    class LruCache(Protocol):
+        def __call__(self, maxsize=None):
+            # type: (Optional[int]) -> Callable[[F], F]
+            raise NotImplementedError
 
 try:
     import ipaddress
@@ -34,6 +45,7 @@
 __all__ = [
     "ipaddress", "uses_pycache", "console_to_str",
     "get_path_uid", "stdlib_pkgs", "WINDOWS", "samefile", "get_terminal_size",
+    "lru_cache",
 ]
 
 
@@ -269,3 +281,15 @@ def ioctl_GWINSZ(fd):
         if not cr:
             cr = (os.environ.get('LINES', 25), os.environ.get('COLUMNS', 80))
         return int(cr[1]), int(cr[0])
+
+
+# Fallback to noop_lru_cache in Python 2
+def noop_lru_cache(maxsize=None):
+    # type: (Optional[int]) -> Callable[[F], F]
+    def _wrapper(f):
+        # type: (F) -> F
+        return f
+    return _wrapper
+
+
+lru_cache = getattr(functools, "lru_cache", noop_lru_cache)  # type: LruCache