charmonium.freeze 0.4.2

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Injectively, deterministically maps objects to hashable, immutable objects.

frozenset is to set as freeze is to Any.

That is, type(a) is type(b) and a != b implies freeze(a) != freeze(b).

Moreover, this function is deterministic, so it can be used to compare states across subsequent process invocations (with the same interpreter major and minor version).

>>> obj = [1, 2, 3, {4, 5, 6}, object()]
>>> hash(obj)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

>>> from charmonium.freeze import freeze
>>> frozen_obj = freeze(obj)
>>> frozen_obj
(1, 2, 3, frozenset({4, 5, 6}), ('object',))

It even works on custom types.

>>> # Make a custom type
>>> class Struct:
...     pass
>>> s = Struct()
>>> s.attr = 4
>>> freeze(s)
('Struct', (('attr', 4),))

Special cases

• freeze on functions returns their bytecode, constants, and closure-vars. This means that freeze_state(f) == freeze_state(g) implies f(x) == g(x). The remarkable thing is that this is true across subsequent invocations of the same process. If the user edits the script and changes the function, then it’s freeze_state will change too.

• freeze on objects returns the objects that would be used by pickle from __reduce__, __reduce_ex__, __getnewargs__, __getnewargs_ex__, and __getstate__. The simplest of these to customize your object __gestate__. See the pickle documentation for details.

• In the cases where __getstate__ is already defined for pickle, and this definition is not suitable for freeze_state, one may override this with __getfrozenstate__ which takes precedence.

Although, this function is not infallible for user-defined types; I will do my best, but sometimes these laws will be violated. These cases include:

• Cases where __eq__ makes objects equal despite differing attributes or inversely make objects inequal despite equal attributes.

  • This can be mitigated if __getstate__ or __getfrozenstate__