CODEWITHSUNDEEP
pythonpython-typing
Heetola
Heetola

Reputation: 6181

Python typing not working when declaring a variable

I'm using python 3.6, and wanted to use typing, because it's nice, you get better linting and you can catch errors before runtime, also autocomplete will be available.

I have this method :

def add_to_dynamic_dict(filenames_by_satustag: Dict[str, List[str]], status_tag: str, filename: str) -> Dict[str, List[str]]:

So before calling it I created a dictionary like this :

filenames_by_satustag = Dict[str, List[str]]

But when running the script I get

TypeError: typing.Dict[str, typing.List[str]] is not a generic class

on that line.

But it is correct according to the documentation :

https://docs.python.org/3.6/library/typing.html (26.1.1 type aliases, second bloc)

What did I do wrong?

Thanks.

Upvotes: 0

Views: 629

Answers (1)

Tristan Nemoz
Tristan Nemoz

Reputation: 2048

I think you are confused with type aliases. The method you declare expects a first argument, which you called filenames_by_satustag with type Dict[str, List[str]]. However, if I'm not mistaken, you call your method with a variable filenames_by_satustag which has value Dict[str, List[str]]. Hence, its type is the type of Dict[str, List[str]], that is typing._GenericAlias. If you want to create a new type called filenames_by_satustag, you should do the following:

filenames_by_satustag = Dict[str, List[str]]

# The function return can also be replaced by filenames_bu_satustag
def add_to_dynamic_dict(some_variable: filenames_by_satustag, status_tag: str, filename: str) -> Dict[str, List[str]]:

If what you wanted, however, was not to create a type alias, but just to create a variable filenames_by_satustag, you could do it like this:

filenames_by_satustag: Dict[str, List[str]] = {}

Upvotes: 2

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