My code is checking only 1 if condition in a function

Question

def check(str):
    if(str.isalnum())==True:
        return True
    if(str.isalpha())==True:
        return True
    if(str.isdigit())==True:
        return True
    if(str.islower())==True:
        return True
    if(str.isupper())==True:
        return True


if __name__ == '__main__':
    s = input()
    if(check(s)):
        print('True')
    else:
        print('False')

It is showing only one condition's result. For example, if I type qA2 it is showing one True instead of

True
True
True
True
True

@engineero a better close would be to find the dupe IMO and close with that instead of a custom reason — roganjosh, Sep 20 '19 at 16:38
Minor stylistic point: in most languages, there's no reason to explicitly compare to `true` and `false`. — EJoshuaS - Stand with Ukraine, Sep 20 '19 at 16:41
@Austin not so sure. I'm on a phone so it's tough to search properly. Touches on the issue but I think there's a canonical. I just can't think of it :/ — roganjosh, Sep 20 '19 at 16:42

score 1 · Accepted Answer · answered Sep 20 '19 at 16:41

This is because you are "returning" from the function if one of the if conditions evaluates to true.

You can read more about the keyword return here. The gist is, as the word says, it "returns" from the function with specified value(s).

If you want the other if conditions to get evaluated too, you will need to maintain a small data structure of all successful if conditions, eg:

def check(str):
    # let's initialise a dictionary with all False values.
    # If any if condition turns True, then we will set 
    # that value to True in the dictionary.
    res = {
        "isalnum":False,
        "isalpha":False,
        "isdigit":False,
        "islower":False,
        "isupper":False,
    }

    if(str.isalnum())==True:
        res["isalnum"] = True
    if(str.isalpha())==True:
        res["isalpha"] = True
    if(str.isdigit())==True:
        res["isdigit"] = True
    if(str.islower())==True:
        res["islower"] = True
    if(str.isupper())==True:
        res["isupper"] = True

    return res # This returns a dictionary with all values
if __name__ == '__main__':
    s = input()
    if(check(s)):
        print('True')
    else:
        print('False')

Thanks so much for helping – Stark_Tony Sep 20 '19 at 16:51 — Stark_Tony, Sep 20 '19 at 16:51

score 0 · Answer 2 · answered Sep 20 '19 at 16:36

return leaves the function immediately. The first condition which succeeds will cause the rest to be skipped, the way you defined your function.

If you want to check all the conditions every time, try something like

def check(str):
    whether = True
    if not str.isalnum():
        whether = False
    if not str.isalpha():
        whether = False
    if not str.isdigit():
        whether = False
    if not str.islower():
        whether = False
    if not str.isupper():
        whether = False
    return whether

Printing something in each branch seems excessive, but could certainly be added.

score 0 · Answer 3 · answered Sep 20 '19 at 16:39

return stops the function's execution. Nothing after a return statement will be run, and a function can only have a single return value. If you want to see the result for all conditions, store them in a List or a Dict and return that instead, for example:

def check(str):
    results = {}
    results['isalnum'] = str.isalnum()
    results['isalpha'] = str.isalpha()
    results['isdigit'] = str.isdigit()
    results['islower'] = str.islower()
    results['isupper'] = str.isupper()
    return results

Thanks so much for helping – Stark_Tony Sep 20 '19 at 16:51 — Stark_Tony, Sep 20 '19 at 16:51

My code is checking only 1 if condition in a function

3 Answers3