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Tag: typechecking

Why are type hints for variables not handled as type hints for function parameters?

When writing a function in Python with type hints like this: It translates to this type hint: Optional[Token]. With optional, a None value is accepted too. When writing the same type hint for a class field, it doesn’t behave the same: Here type hint checkers like the integrated one in PyCharm reports: Expected type ‘Token’, got None instead. My questions

Subclassing Sequence with proper type hints in Python

I’m trying to implement a kind of custom sequence class in Python: Now I want to check that mypy is aware that elements of MySequence are items of type T: So it fails: mypy knows nothing about items of foo. The same example for ordinary Sequence works: If I’m trying to add type annotations to __getitem__ implementation, I have another

Use isinstance to test for Unicode string

How can I do something like: But I would like isinstance to return True for this Unicode encoded string. Is there a Unicode string object type? Answer Test for str: or, if you must handle bytestrings, test for bytes separately: The two types are deliberately not exchangible; use explicit encoding (for str -> bytes) and decoding (bytes -> str) to

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