Python Forum

The below has no synthetical or static semantic errors in it, but does not run as expected. Namely, I want my shell to print "string involved" if the type of varA or varB is string; instead it prints nothing. Could anyone help me understand what is wrong with my code and how to fix it?

varA = 1
varB = "A"

if (type(varA) and type(varB)) is (int or float):
    if varA > varB:
        print("bigger")
    if varA == varB:
        print("equal")
    if varA < varB:
        print("smaller")
elif (type(varA) or type(varB)) is str:
    print("string involved")

well, that's one hell of a script..

if (type(varA) and type(varB)) is (int or float):

is same as

if str is int: # and that evaluates to False

and

elif (type(varA) or type(varB)) is str:

is same as

elif int is str: # again evaluates to False

for better understanding read
https://python-forum.io/Thread-Multiple-...or-keyword

that said, checking types in Python is not common practice. Read duck typing
finally, varA is int and varB is str, comparison betwen different types could yield unexpected results

>>> 1>'A'
False
>>> 1=='A'
False
>>> 1<'A'
True
>>>

Usually input is taken as strings. So usually both variables would be a string. In that case you could utilize string methods such as str.isdigit()

Otherwise you should use the isinstance built in rather than type..

if isinstance(varA, (int, float)) and isinstance(varB, (int, float)):
    if varA > varB:
        print("bigger")
    elif varA == varB:
        print("equal")
    elif varA < varB:
        print("smaller")
elif isinstance(varA, str) or isinstance(varB, str):
    print('string involved')

However in python you should ask for forgiveness rather than permission. You can do any variation of try/except here, but here is a version. I kept the checking for string, because you can still make those comparisons with strings, otherwise the if condition wouldn't even be there.

if isinstance(varA, str) or isinstance(varB, str):
    print('string involved')
else:
    try:
        if varA > varB:
            print("bigger")
        elif varA == varB:
            print("equal")
        elif varA < varB:
            print("smaller")
    except TypeError:
        pass

(Oct-02-2017, 02:44 PM)Shellburn Wrote: [ -> ]The below has no synthetical or static semantic errors in it, but does not run as expected.

You don't know what a semantic error is, then.

Shellburn

buran

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