This library provides a simple decorator that allows you to enforce strict type checking in you everyday cPython functions based on the type hint of the function parameters.

What to expect from this decorator?

When you use this decorator in your function, you have to keep in mind a couple of things-

1. This strictly requires type hinting your function parameters & return value
2. If you don't provide type hinting, you'll see some custom exceptions being raised named TypeHintMissingError
3. You can skip the return value strict check, if you want. But function parameters are always type checked
4. If you pass type hinting but the hint don't match with the value type, you'll get a TypeMismatchError
5. You must call your function with Keyword arguments, otherwise you'll get a PositionalArgumentsNotAllowedException

Each error/exception will have helpful message to help you identify what you need to do.

Installation

You can simply install the latest version with this command:

pip install strictpy

If you want any specific older version:

pip install strictpy==1.0.0

Usage

The usage is pretty simple and intuitive. We just need to have our functions decorated with @strict.

Let's start with simple example:

from strictpy import strict

@strict
def some_function(x: int, y: int) -> int:
    return x * y

some_function(x=5, y=6)

This will lead to execution of the function with no visible difference as all the arguments and the return value is type hinted. Also, the function is called with Keyword arguments, which is a must if you use @strict decorator.

Now, let's see an example what happens if type hints are missing:

from strictpy import strict

@strict
def some_function(x: int, y: int):
    return x * y

some_function(x=5, y=6)

If you run this code, you'll get the following exception because the return type hint is missing:

...
File "/Users/ishmam/PycharmProjects/strict-py/src/strictpy/helpers.py", line 14, in ensure_return_type_hint
    raise TypeHintMissingError("return type hint cannot be empty.")
strictpy.exceptions.TypeHintMissingError: return type hint cannot be empty.

Although, you can skip check for return type check like this:

from strictpy import strict

@strict(force_return_type_check=False)
def some_function(x: int, y: int):
    return x * y

some_function(x=5, y=6)

This will ignore the return value missing type hint.

In this last example you'll see the exception that is raised when the function is called with Positional arguments:

from strictpy import strict

@strict(force_return_type_check=False)
def some_function(x: int, y: int):
    return x * y

some_function(5, y=6) # x is positional

Raised exception:

File "/Users/ishmam/PycharmProjects/strict-py/src/strictpy/helpers.py", line 33, in ensure_keyword_only_arguments
    raise PositionalArgumentsNotAllowedException(
strictpy.exceptions.PositionalArgumentsNotAllowedException: Only keyword arguments are expected, 1 were passed as positional arguments.