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gh-121192: Add fast path to deepcopy() for empty list/tuple/dict/set #121193

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lgeiger wants to merge 5 commits into from
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gh-121192: Add fast path to deepcopy() for empty list/tuple/dict/set #121193

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f317c1b
Optimize deepcopy of empty containers
lgeiger Jun 30, 2024
943a10f
Remove special case for tuple and frozensets
lgeiger Jun 30, 2024
68c589f
Add NEWS entry
lgeiger Jun 30, 2024
ba7298c
Don't call len for checking for empty container
lgeiger Jul 1, 2024
d87901e
Revert optimization for nested empty containers
lgeiger Jul 2, 2024
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Optimize deepcopy of empty containers
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@lgeiger
lgeiger committed Jun 30, 2024
commit f317c1b3979d1382201f369c476993b517ef2b1e
14 changes: 10 additions & 4 deletions Lib/copy.py
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Original file line number Diff line number Diff line change
Expand Up @@ -123,19 +123,23 @@ def deepcopy(x, memo=None, _nil=[]):

cls = type(x)

if cls in _atomic_types:
if cls in _atomic_types or (cls in _immutable_iterables and len(x) == 0):
return x

d = id(x)
if memo is None:
if cls in _mutable_iterables and len(x) == 0:
return cls()
d = id(x)
memo = {}
else:
d = id(x)
y = memo.get(d, _nil)
if y is not _nil:
return y

copier = _deepcopy_dispatch.get(cls)
if copier is not None:
if cls in _mutable_iterables and len(x) == 0:
y = cls()
elif copier := _deepcopy_dispatch.get(cls):
y = copier(x, memo)
else:
if issubclass(cls, type):
Expand Down Expand Up @@ -173,6 +177,8 @@ def deepcopy(x, memo=None, _nil=[]):
_atomic_types = {types.NoneType, types.EllipsisType, types.NotImplementedType,
int, float, bool, complex, bytes, str, types.CodeType, type, range,
types.BuiltinFunctionType, types.FunctionType, weakref.ref, property}
_mutable_iterables = {list, dict, set}
_immutable_iterables = {tuple, frozenset}

_deepcopy_dispatch = d = {}

Expand Down