gh-108751: Add copy.replace() function - #108752
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It creates a modified copy of an object by calling the object's __replace__() method. It is a generalization of dataclasses.replace(), named tuple's _replace() method and replace() methods in various classes, and supports all these stdlib classes.
| single: __replace__() (replace protocol) | ||
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| Function :func:`replace` is more limited than :func:`copy` and :func:`deepcopy`, | ||
| and only supports named tuples, dataclasses, and other classes which |
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| and only supports named tuples, dataclasses, and other classes which | |
| and only supports :term:`named tuples <named tuple>`, :mod:`dataclasses`, and other classes which |
(I haven’t double checked if named tuple or namedtuple is the right key)
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Actually, it does not support named tuples in general. It currently only supports named tuples created by collections.namedtuple().
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| func = getattr(cls, '__replace__', None) | ||
| if func is None: | ||
| raise TypeError(f"replace() does not support {cls.__name__} objects") | ||
| return func(obj, **changes) |
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This is a cool feature for very little code!
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There's a new commit after the PR has been approved. @rhettinger: please review the changes made to this pull request. |
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This change introduced a regression: see issue #109052. With this change, test_sys_settrace started to crash. I don't know if the bug already existed before and was hidden, or if the Objects/codeobject.c change really introduced a regression. |
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| * Add :func:`copy.replace` function which allows to create a modified copy of | ||
| an object, which is especially usefule for immutable objects. |
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usefule -> useful
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Thanks. Do you mind to create a PR to fix this typo?
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Would it make sense to add support for dict? >>> d={'x': 1}
>>> copy.replace(d, x=2)
TypeError: replace() does not support dict objectsIt would be an alternative to: >>> d={'x': 1}
>>> dict(d, x=2)
{'x': 2}
>>> {**d, 'x': 2}
{'x': 2} |
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Nice feature. |
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Perhaps no, because it erodes the difference between an object and a dict (as in JavaScript). And you already have other ways to do this with dicts. |
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It creates a modified copy of an object by calling the object's __replace__() method.
It is a generalization of dataclasses.replace(), named tuple's _replace() method and replace() methods in various classes, and supports all these stdlib classes.
📚 Documentation preview 📚: https://cpython-previews--108752.org.readthedocs.build/