Merge pull request #9835 from jamescurtin/9831-bugfix

Fix import error introduced in 21.1

news/9831.bugfix.rst

@@ -0,0 +1 @@
+This change fixes a bug on Python <=3.6.1 with a Typing feature added in 3.6.2

src/pip/_internal/req/req_file.py

@@ -8,17 +8,7 @@
 import shlex
 import urllib.parse
 from optparse import Values
-from typing import (
-    TYPE_CHECKING,
-    Any,
-    Callable,
-    Dict,
-    Iterator,
-    List,
-    NoReturn,
-    Optional,
-    Tuple,
-)
+from typing import TYPE_CHECKING, Any, Callable, Dict, Iterator, List, Optional, Tuple
 
 from pip._internal.cli import cmdoptions
 from pip._internal.exceptions import InstallationError, RequirementsFileParseError
@@ -29,6 +19,10 @@
 from pip._internal.utils.urls import get_url_scheme, url_to_path
 
 if TYPE_CHECKING:
+    # NoReturn introduced in 3.6.2; imported only for type checking to maintain
+    # pip compatibility with older patch versions of Python 3.6
+    from typing import NoReturn
+
     from pip._internal.index.package_finder import PackageFinder
 
 __all__ = ['parse_requirements']

src/pip/_internal/utils/hashes.py

@@ -1,12 +1,16 @@
 import hashlib
-from typing import TYPE_CHECKING, BinaryIO, Dict, Iterator, List, NoReturn
+from typing import TYPE_CHECKING, BinaryIO, Dict, Iterator, List
 
 from pip._internal.exceptions import HashMismatch, HashMissing, InstallationError
 from pip._internal.utils.misc import read_chunks
 
 if TYPE_CHECKING:
     from hashlib import _Hash
 
+    # NoReturn introduced in 3.6.2; imported only for type checking to maintain
+    # pip compatibility with older patch versions of Python 3.6
+    from typing import NoReturn
+
 
 # The recommended hash algo of the moment. Change this whenever the state of
 # the art changes; it won't hurt backward compatibility.