Using the typing.List generic alias, I can only specify a single type.
Example:
>>> typing.List[int]
typing.List[int]
When I try to specify additional types, it fails. Example:
>>> typing.List[int, int]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.9/typing.py", line 243, in inner
return func(*args, **kwds)
File "/usr/lib/python3.9/typing.py", line 775, in __getitem__
_check_generic(self, params, self._nparams)
File "/usr/lib/python3.9/typing.py", line 197, in _check_generic
raise TypeError(f"Too {'many' if alen > elen else 'few'} parameters for
{cls};"
TypeError: Too many parameters for typing.List; actual 2, expected 1
This makes sense to me. An item has one type, and we use Union if we
want variants. What's not making sense to me in Python 3.9: I can use
the built-in generic alias in list in this manner, apparently
successfully:
>>> list[int, int]
list[int, int]
In fact, it appears I can specify an indeterminate number of types. Can
someone explain what this construct means? I suspect this will fail to
be interpreted by type validators, but wonder why it doesn't fail fast
when I express it.
Thanks,
Paul
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