BUG: stats._distribution_infrastructure._Domain.symbols class attribute is shared by instances

[jorenham]

Describe your issue.

The following class attribute is defined in scipy.stats._distribution_infrastructure._Domain:

scipy/scipy/stats/_distribution_infrastructure.py

Line 216 in e7dfd40

symbols = {np.inf: r"\infty", -np.inf: r"-\infty", np.pi: r"\pi", -np.pi: r"-\pi"}

Its subclass, _SimpleDomain, mutates it in an instance method:

scipy/scipy/stats/_distribution_infrastructure.py

Line 297 in e7dfd40

self.symbols.update(new_symbols)

... even though _Domain.__init___ doesn't shadow it (i.e. self.symbols = ...):

scipy/scipy/stats/_distribution_infrastructure.py

Lines 269 to 274 in e7dfd40

	def __init__(self, endpoints=(-inf, inf), inclusive=(False, False)):
	a, b = endpoints
	self.endpoints = np.asarray(a)[()], np.asarray(b)[()]
	self.inclusive = inclusive
	# self.all_inclusive = (endpoints == (-inf, inf)
	# and inclusive == (True, True))

So as far as I can tell, it's directly updated on the class state, and therefore shared between all instances. I don't see why this would be intended behaviour, so I thought I'd let you know.

This is relevant to the current main branch, and I spotted this in the 1.15.0rc1 release.

Reproducing Code Example

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Error message

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SciPy/NumPy/Python version and system information

irrelevant

[mdhaber]

Thanks @jorenham. Yeah, I'll want to revisit that system at some point to see if I can simplify things. In the meantime, I think it would be sufficient to just copy it in the _SimpleDomain initializer (gh-22139).

[jorenham]

I'll update jorenham/scipy-stubs#360 accordingly (remove the ClassVar) 👌🏻