RustPython · youknowone · Jan 20, 2026 · Jan 18, 2026 · Jan 20, 2026
diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
@@ -29,6 +29,9 @@
 import _collections_abc
 import sys as _sys
 
+_sys.modules['collections.abc'] = _collections_abc
+abc = _collections_abc
+
 from itertools import chain as _chain
 from itertools import repeat as _repeat
 from itertools import starmap as _starmap
@@ -46,7 +49,8 @@
     _collections_abc.MutableSequence.register(deque)
 
 try:
-    from _collections import _deque_iterator
+    # Expose _deque_iterator to support pickling deque iterators
+    from _collections import _deque_iterator  # noqa: F401
 except ImportError:
     pass
 
@@ -59,6 +63,8 @@
     # with this instead.
     from ._defaultdict import defaultdict
 
+heapq = None  # Lazily imported
+
 
 ################################################################################
 ### OrderedDict
@@ -461,7 +467,7 @@ def _make(cls, iterable):
     def _replace(self, /, **kwds):
         result = self._make(_map(kwds.pop, field_names, self))
         if kwds:
-            raise ValueError(f'Got unexpected field names: {list(kwds)!r}')
+            raise TypeError(f'Got unexpected field names: {list(kwds)!r}')
         return result
 
     _replace.__doc__ = (f'Return a new {typename} object replacing specified '
@@ -499,6 +505,7 @@ def __getnewargs__(self):
         '_field_defaults': field_defaults,
         '__new__': __new__,
         '_make': _make,
+        '__replace__': _replace,
         '_replace': _replace,
         '__repr__': __repr__,
         '_asdict': _asdict,
@@ -592,7 +599,7 @@ class Counter(dict):
     # References:
     #   http://en.wikipedia.org/wiki/Multiset
     #   http://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html
-    #   http://www.demo2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm
+    #   http://www.java2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm
     #   http://code.activestate.com/recipes/259174/
     #   Knuth, TAOCP Vol. II section 4.6.3
 
@@ -632,7 +639,10 @@ def most_common(self, n=None):
             return sorted(self.items(), key=_itemgetter(1), reverse=True)
 
         # Lazy import to speedup Python startup time
-        import heapq
+        global heapq
+        if heapq is None:
+            import heapq
+
         return heapq.nlargest(n, self.items(), key=_itemgetter(1))
 
     def elements(self):
@@ -642,7 +652,8 @@ def elements(self):
         >>> sorted(c.elements())
         ['A', 'A', 'B', 'B', 'C', 'C']
 
-        # Knuth's example for prime factors of 1836:  2**2 * 3**3 * 17**1
+        Knuth's example for prime factors of 1836:  2**2 * 3**3 * 17**1
+
         >>> import math
         >>> prime_factors = Counter({2: 2, 3: 3, 17: 1})
         >>> math.prod(prime_factors.elements())
@@ -683,7 +694,7 @@ def update(self, iterable=None, /, **kwds):
 
         '''
         # The regular dict.update() operation makes no sense here because the
-        # replace behavior results in the some of original untouched counts
+        # replace behavior results in some of the original untouched counts
         # being mixed-in with all of the other counts for a mismash that
         # doesn't have a straight-forward interpretation in most counting
         # contexts.  Instead, we implement straight-addition.  Both the inputs
@@ -1018,7 +1029,7 @@ def __getitem__(self, key):
         return self.__missing__(key)            # support subclasses that define __missing__
 
     def get(self, key, default=None):
-        return self[key] if key in self else default
+        return self[key] if key in self else default    # needs to make use of __contains__
 
     def __len__(self):
         return len(set().union(*self.maps))     # reuses stored hash values if possible
@@ -1030,7 +1041,10 @@ def __iter__(self):
         return iter(d)
 
     def __contains__(self, key):
-        return any(key in m for m in self.maps)
+        for mapping in self.maps:
+            if key in mapping:
+                return True
+        return False
 
     def __bool__(self):
         return any(self.maps)
@@ -1040,9 +1054,9 @@ def __repr__(self):
         return f'{self.__class__.__name__}({", ".join(map(repr, self.maps))})'
 
     @classmethod
-    def fromkeys(cls, iterable, *args):
-        'Create a ChainMap with a single dict created from the iterable.'
-        return cls(dict.fromkeys(iterable, *args))
+    def fromkeys(cls, iterable, value=None, /):
+        'Create a new ChainMap with keys from iterable and values set to value.'
+        return cls(dict.fromkeys(iterable, value))
 
     def copy(self):
         'New ChainMap or subclass with a new copy of maps[0] and refs to maps[1:]'
@@ -1485,6 +1499,8 @@ def format_map(self, mapping):
         return self.data.format_map(mapping)
 
     def index(self, sub, start=0, end=_sys.maxsize):
+        if isinstance(sub, UserString):
+            sub = sub.data
         return self.data.index(sub, start, end)
 
     def isalpha(self):
@@ -1553,6 +1569,8 @@ def rfind(self, sub, start=0, end=_sys.maxsize):
         return self.data.rfind(sub, start, end)
 
     def rindex(self, sub, start=0, end=_sys.maxsize):
+        if isinstance(sub, UserString):
+            sub = sub.data
         return self.data.rindex(sub, start, end)
 
     def rjust(self, width, *args):

diff --git a/Lib/collections/abc.py b/Lib/collections/abc.py