strict.py

# Type-checked functions in python (!)
# This is a terrible idea

embeddings = {}

def signature(*sigtypes):
    def decorator(func):
        def wrapped(*args):
            types = sigtypes
            if types[-1] == Ellipsis:
                extra_types = (types[-2], ) * (len(args) - len(types) + 2)
                types = types[:-2] + extra_types
            if len(types) != len(args):
                print(types)
                raise TypeError("Wrong number of arguments")
            newargs = []
            for arg, t in zip(args, types):
                while not isinstance(arg, t):
                    if type(arg) not in embeddings:
                        raise TypeError("Type mismatch")
                    arg = embeddings[type(arg)](arg)
                newargs.append(arg)
            return func(*newargs)
        return wrapped
    return decorator

embeddings[int] = float
embeddings[str] = int

@signature(int)
def square(x):
    print(x ** 2)

print("3 squared is", square(3))
try:
    square(None)
except TypeError as e:
    print("square(None) gave", e)


@signature(str, float, ...)
def printsum(message, *nums):
    print(message, sum(nums))

printsum("The sum is", 1, 2, 3.1, 4.4, '5')
printsum("The sum is")