copy

The copy module makes copies of arbitrary objects. Shallow copies duplicate the outer container; deep copies recurse, sharing identity inside cycles via a memo dict.

Source-of-record: Lib/copy.py, copy docs.

API

Function	Effect
copy.copy(x)	Shallow copy.
copy.deepcopy(x, memo=None)	Recursive copy preserving sharing via memo.
copy.replace(obj, /, **changes)	Functional update (3.13+).

Hooks

Method	Role
__copy__(self)	Override copy.copy.
__deepcopy__(self, memo)	Override copy.deepcopy.
__replace__(self, /, **changes)	Override copy.replace.
__reduce__, __reduce_ex__	Used as a fallback (same protocol as pickle).
__getstate__, __setstate__	Component of the pickle protocol used by deep copy.

Algorithm

1. Look up a per-type dispatch table (built-ins).
2. If a class has __deepcopy__, call it with memo.
3. Otherwise call __reduce_ex__(4) and reconstruct.
4. Atomic types (numbers, strings, frozenset, code, modules, types, ranges, functions, classes) are returned as-is.

memo is keyed by id(obj). Self-referential graphs round-trip correctly because the memo records the new object before recursing.

Exceptions

copy.Error wraps copy-time failures. Typed as Exception.

Gopy status

Area	State
copy, deepcopy	Complete.
Hook dispatch (__copy__, __deepcopy__)	Complete.
__reduce_ex__ fallback	Complete.
copy.replace	Complete.

Reference

• CPython 3.14: copy.
• Lib/copy.py.
• module/copy/. gopy port.