From e712a5b277866a71c195f38c1b5d87d9126dba3e Mon Sep 17 00:00:00 2001
From: "Jason R. Coombs" <jaraco@jaraco.com>
Date: Thu, 30 Dec 2021 21:00:48 -0500
Subject: bpo-46118: Move importlib.resources to its own package. (#30176)

* bpo-46118: Move importlib.resources to its own package.

* Expand compatibility shims with documentation and explicit imports.
---
 Lib/importlib/resources/_itertools.py | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 Lib/importlib/resources/_itertools.py

(limited to 'Lib/importlib/resources/_itertools.py')

diff --git a/Lib/importlib/resources/_itertools.py b/Lib/importlib/resources/_itertools.py
new file mode 100644
index 00000000000..cce05582ffc
--- /dev/null
+++ b/Lib/importlib/resources/_itertools.py
@@ -0,0 +1,35 @@
+from itertools import filterfalse
+
+from typing import (
+    Callable,
+    Iterable,
+    Iterator,
+    Optional,
+    Set,
+    TypeVar,
+    Union,
+)
+
+# Type and type variable definitions
+_T = TypeVar('_T')
+_U = TypeVar('_U')
+
+
+def unique_everseen(
+    iterable: Iterable[_T], key: Optional[Callable[[_T], _U]] = None
+) -> Iterator[_T]:
+    "List unique elements, preserving order. Remember all elements ever seen."
+    # unique_everseen('AAAABBBCCDAABBB') --> A B C D
+    # unique_everseen('ABBCcAD', str.lower) --> A B C D
+    seen: Set[Union[_T, _U]] = set()
+    seen_add = seen.add
+    if key is None:
+        for element in filterfalse(seen.__contains__, iterable):
+            seen_add(element)
+            yield element
+    else:
+        for element in iterable:
+            k = key(element)
+            if k not in seen:
+                seen_add(k)
+                yield element
-- 
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