CODEWITHSUNDEEP
pythonpython-typing
Gordon Mckeown
Gordon Mckeown

Reputation: 752

Satisfying Python type checking for values from a dictionary

I have a Python script that pulls in some config variables using dotenv_values and sets some initial constants using these. The constants are then passed as arguments to a function. If I define the constants in the global context, I get a type-checking error due to the function expecting a string. If I define the constants within the main function, the type checking is fine (although it doesn't like me using the constant naming style within main).

Here's a simple script that should demonstrate the issue:

"""Type-checking test"""

from dotenv import dotenv_values

config = dotenv_values(".config")
URL = config.get("BASE_URL")
if URL is None:
    raise ValueError("BASE_URL is not set in .config file")


def do_a_thing(url: str) -> None:
    """Do a thing"""
    print("You passed in a URL:", url)


def main():
    """Main"""

    do_a_thing(URL)


if __name__ == "__main__":
    main()

This results in the checker flagging the "do_a_thing(URL)" line with:

Argument of type "str | None" cannot be assigned to parameter "url" of type "str" in function "do_a_thing"
  Type "str | None" is not assignable to type "str"
    "None" is not assignable to "str"

How can I convince the type checker that the do_a_thing function will never be called with a None value?

Upvotes: 0

Views: 68

Answers (0)

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