[Python] Type-hinting parameters with a sentinel value as the default

I currently use this strategy when I cannot assign default arguments in a function's signature and/or None already has meaning.

from typing import Optional

DEFAULT = object()


# `None` already has meaning.
def spam(ham: Optional[list[str]] = DEFAULT):
if ham is DEFAULT:
ham = ['prosciutto', 'jamon']
if ham is None:
print('Eggs?')
else:
print(str(len(ham)) + ' ham(s).')


Error:

Failed (exit code: 1) (2607 ms)

main.py:7: error: Incompatible default for argument "ham" (default has type "object", argument has type "Optional[List[str]]")
Found 1 error in 1 file (checked 1 source file)

• How do I type-hint ham without getting errors in mypy? or
• What strategy should I use instead of DEFAULT = object()?

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