How to check if the input string is an integer

Question

if input()==int():
    print('mission successful!')
else:
    print('mission failed!')

for above code the problem is, that it never results in mission successful even though my input is integer.

I have just started learning python.

It's important to know that input() will not give you an integer, but a string, even if you input a number. — Shinra tensei
– Shinra tensei, Commented Jul 24, 2017 at 11:42
Possible duplicate of How to check if string input is a number? — Chris_Rands
– Chris_Rands, Commented Jul 24, 2017 at 13:44

Alexander · Accepted Answer · 2021-05-02 20:31:22Z

2

To check if the input string is numeric, you can use this:

s = input()
if s.isnumeric() or (s.startswith('-') and s[1:].isdigit()):
    print('mission successful!')
else:
    print('mission failed!')

In Python, checking if a string equals a number will always return False. In order to compare strings and numbers, it helps to either convert the string to a number or the number to a string first. For example:

>>> "1" == 1
False
>>> int("1") == 1
True

or

>>> 1 == "1"
False
>>> str(1) == "1"
True

If a string can not be converted to a number with int, a ValueError will be thrown. You can catch it like this:

try:
    int("asdf")
except ValueError:
    print("asdf is not an integer")

edited May 2, 2021 at 20:31

answered Jul 24, 2017 at 11:54

Alexander

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1 Comment

Chris_Rands Over a year ago

First method fails for negative ints or floats

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