Pylance incorrectly marks default parameters as a type issue #2879
Comments
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You still need to add None as a type. python 3.10 def foo(a: str | None = None):
...else from typing import Optional
def foo(a: Optional[str] = None):
... |
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I want to clarify that the above is not sufficient. By typing it explicitly as t = foo(a=None)However I want to explicitly disallow this such that the user can ONLY pass in value of type |
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If the function is written to accept a |
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@lee-hyunkyu, is your goal to be able to tell whether the caller (explicitly) provided a value for that parameter? |
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@erictraut This is a flow that is supported by
As @debonte mentioned, one reason might be to determine whether the caller explicitly provided a value or not. Another is that it's a bit of a code smell for a user to use the function above by passing in # v1
def foo(a: str = None):
if a is None:
return "foo"
else:
return f"foo {a}"
# v2
def foo(a: Optional[str] = 1):
# a should be of type `str | int | None`
if type(a, int):
return "foo"
else if a is None:
return "foo None"
else:
return f"foo {a}"
## usage
# v1
foo(a=None) # "foo"
foo() # "foo"
# v2
foo(a=None) # "foo None"
foo() # "foo"The default behavior has remained the same (we return |
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@debonte In case my previous comment didn't answer your question, no my goal isn't to tell whether a value was explicitly provided. I can't think of a scenario where that would matter but someone else might have a use for that functionality |
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@lee-hyunkyu, mypy implicitly interprets a parameter with a def foo(a: str = None):
...
foo(a=None)This implicit interpretation of Here's the relevant section of PEP 484: If you want the old behavior, pyright has an option to enable it. Look for |
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@erictraut Hmm, I seemed to have completely misunderstood Given that and the PEPs, I'll close. Thanks for the clarification. |
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@lee-hyunkyu, if you want to enforce that callers never pass @overload
def foo() -> str: ...
@overload
def foo(a: str) -> str: ...
def foo(a: str | None = None):
if a is None:
return "foo"
else:
return f"foo {a}" |
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@erictraut That's incredibly helpful! I hadn't thought to use overloads to achieve the behavior I want. |
Environment data
Code Snippet
Expected behavior
I expect this to not throw an type check error and
ato be typed asOptional[str]withinfoo.Actual behavior
ais typed asstrand this raises areportGeneralTypeIssueserrorLogs
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