How to tell PyCharm what type a parameter is expected to be?

How to tell PyCharm what type a parameter is expected to be?

In PyCharm, you can use type hints to specify the expected type of a parameter in a function or method. Type hints are annotations that provide information about the expected types of variables, function parameters, and return values. PyCharm uses these type hints to provide better code analysis, autocompletion, and code inspections.

Here's how you can tell PyCharm what type a parameter is expected to be using type hints:

  1. Use Python 3.5+ Type Hints: PyCharm fully supports Python type hints introduced in Python 3.5 and later. You can use annotations to specify the expected type of a parameter by adding a colon (:) after the parameter name, followed by the type.

    def greet(name: str) -> str: return f"Hello, {name}!"

    In this example, the name parameter is annotated with the type hint str, indicating that it should be a string.

  2. Use Type Comments (for Python 2 or when necessary): If you're working with older versions of Python (Python 2) or if you prefer not to use type hints in function signatures, you can use type comments to specify the expected type of a parameter. Type comments are placed as comments immediately after the parameter.

    def greet(name): # type: (str) -> str return f"Hello, {name}!"

    In this case, the comment # type: (str) -> str provides the same information as a type hint, indicating that name should be a string, and the function returns a string.

  3. Use Type Aliases: You can also use type aliases to define custom types and reuse them in your function signatures. This can make your code more readable and maintainable.

    from typing import List def process_numbers(numbers: List[int]) -> int: total = sum(numbers) return total

    In this example, List[int] is a type alias indicating that the numbers parameter should be a list of integers.

PyCharm will use these type hints and comments to provide you with code suggestions, autocompletion, and help you catch type-related errors early in your development process.

Additionally, you can configure PyCharm to perform more advanced type checking using tools like mypy, which can further enhance type checking and static analysis of your code.

Examples

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