CODEWITHSUNDEEP
pythonpython-3.x
Brock Dehler
Brock Dehler

Reputation: 11

Printing "Wrong Type" when calling a function with the wrong input type - Python

I'm trying to make an error message appear when the wrong type of data is entered into a function. In this instance, I am only trying to accept an int or float when the function is called. Entering a str in the function should return an error message

def isPrime(i):

    if not (type(i)==float or type(i)==int):
        print("Input wrong type")
        return None

    i = abs(int(i))

    if i == 2 or i == 1: 
        return True    

    if not i & 1: 
        return False

    for x in range(3, int(i**0.5) + 1, 2):
        if i % x == 0:
            return False

    return True

# Wanting the code to return an error
isPrime(bob)

Upvotes: 1

Views: 2529

Answers (2)

blhsing
blhsing

Reputation: 106768

If you're using Python 3.5+, you can use type hint with the following decorator (which I adapted from @MartijnPieters's typeconversion decorator) to enforce the type hints:

import functools
import inspect

def enforce_types(f):
    sig = inspect.signature(f)
    @functools.wraps(f)
    def wrapper(*args, **kwargs):
        bound = sig.bind(*args, **kwargs)
        bound.apply_defaults()
        args = bound.arguments
        for param in sig.parameters.values():
            if param.annotation is not param.empty and not isinstance(args[param.name], param.annotation):
                raise TypeError("Parameter '%s' must be an instance of %s" % (param.name, param.annotation))
        result = f(*bound.args, **bound.kwargs)
        if sig.return_annotation is not sig.empty and not isinstance(result, sig.return_annotation):
            raise TypeError("Returning value of function '%s' must be an instance of %s" % (f.__name__, sig.return_annotation))
        return result
    return wrapper

@enforce_types
def isPrime(i: float) -> bool:
    i = abs(int(i))
    if i == 2 or i == 1: 
        return True    
    if not i & 1: 
        return False
    for x in range(3, int(i**0.5) + 1, 2):
        if i % x == 0:
            return False
    return True

so that:

print(isPrime(1))
print(isPrime(1.0))

would both output True, but:

print(isPrime('one'))

would raise the following exception:

TypeError: Parameter 'i' must be an instance of <class 'float'>

Upvotes: 2

U13-Forward
U13-Forward

Reputation: 71580

So:

if not (type(i)==float or type(i)==int):
    print("Input wrong type")
    return None

Could be simplified to:

if not isinstance(i,(float,int)):
    print("Input wrong type")
    return None

Then do error message:

if not isinstance(i,(float,int)):
    raise TypeError('Your Text here') #You can do any error i do `TypeError` just for now.

Then to create own Error message:

class MyError(Exception):
    pass

Then here:

if not isinstance(i,(float,int)):
    raise MyError('Your Text here')

But I'll prefer to use TypeError, for doing errror

Upvotes: 0

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