pythonnative/src/pythonnative/equality.py at main · pythonnative/pythonnative · GitHub

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"""The one equality rule the framework applies to application values.

Hook dependencies, state setters, ``memo`` props, native prop diffing, and

context values all decide "did this change?" with

[`equal`][pythonnative.equality.equal]:

1. The same object is equal to itself.

2. Callables (handlers, closures, components) are equal only by identity;

a fresh closure always counts as a change, which is why

[`use_callback`][pythonnative.use_callback] exists. Bound methods are

the exception: Python creates a new method object on every attribute

access, so ``store.subscribe`` equals ``store.subscribe`` when both

bind the same function to the same object.

3. Everything else compares with ``==``, and only a plain ``bool``

result counts. Objects whose comparison returns something else (NumPy

arrays) or raises are treated as changed, so a new identity is the

way to signal an update.

Consequences worth knowing: mutating a list, dict, or set in place and

passing the same object back never re-renders (the setter sees the same

identity), and two equal-but-distinct dataclass instances do not.

"""

from types import MethodType

from typing import Any, Mapping

__all__ = ["equal", "equal_props"]

def equal(left: Any, right: Any) -> bool:

"""Return whether two values are equal under the framework rule (see the module docstring)."""

if left is right:

return True

if isinstance(left, MethodType) and isinstance(right, MethodType):

return left.__self__ is right.__self__ and left.__func__ is right.__func__

if callable(left) or callable(right):

return False

try:

result = left == right

except Exception:

return False

return result if isinstance(result, bool) else False

def equal_props(old: Mapping[str, Any], new: Mapping[str, Any]) -> bool:

"""Return whether two prop mappings have the same keys and [`equal`][pythonnative.equality.equal] values.

This is the default comparator behind [`memo`][pythonnative.memo].

"""

if old is new:

return True

if old.keys() != new.keys():

return False

return all(equal(value, new[key]) for key, value in old.items())

pythonnative/src/pythonnative/equality.py at main · pythonnative/pythonnative · GitHub

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