marcus-g
9/16/2017 - 5:10 PM

Function Type Checking Using a Decorator

A decorator that helps to check input arguments for type

From https://www.safaribooksonline.com/library/view/python-cookbook-3rd/9781449357337/ch09s07.html

from inspect import signature
from functools import wraps

def typeassert(*ty_args, **ty_kwargs):
    def decorate(func):
        # If in optimized mode, disable type checking
        if not __debug__:
            return func

        # Map function argument names to supplied types
        sig = signature(func)
        bound_types = sig.bind_partial(*ty_args, **ty_kwargs).arguments

        @wraps(func)
        def wrapper(*args, **kwargs):
            bound_values = sig.bind(*args, **kwargs)
            # Enforce type assertions across supplied arguments
            for name, value in bound_values.arguments.items():
                if name in bound_types:
                    if not isinstance(value, bound_types[name]):
                      raise TypeError(
                        'Argument {} must be {}'.format(name, bound_types[name])
                        )
            return func(*args, **kwargs)
        return wrapper
    return decorate
  
""" in use
@typeassert(int, int)
... def add(x, y):
...     return x + y
"""