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Python Comparison Solution

Posted by Marco Koopman
Marco Koopman
5,290 Points

How to check if input is int and not string or float

number = input("Please enter a number: ")

number = int(number)

This is the 'right' code if you follow the video. But when the input is a string the code breaks. How can you check if the input is a int?

Rohan Tinna
Rohan Tinna
3,415 Points
Rohan Tinna
Rohan Tinna
3,415 Points

You can use the type function in Python. The syntax is as follows: type(object) This function will return the type of the object passed in as argument (inside the brackets).

number = input("Enter a number:  ")
print(type(number))

# Now if we cast the number variable (now a string because input function returns a string) to an int and check the type again, we'll get a different result.

number = int(number)
print(type(number))

The output of the above python code (if you enter 3 as input) will be:

Enter a number: 3
<class 'str'>
<class 'int'>

This indicated that initially, the data type of number variable was a string (str) but when we casted it to an integer and printed out it data type again, it was changed to integer (int).

I hope this answer will help you out ;)

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3 Answers

Joey Bruijns
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Joey Bruijns
Full Stack JavaScript Techdegree Graduate 47,878 Points
Joey Bruijns
.a{fill-rule:evenodd;}techdegree seal-36
Joey Bruijns
Full Stack JavaScript Techdegree Graduate 47,878 Points

Hi Marco,

You can use a try/except block for this kind of work:

try:
    number = input("Please enter a number: ")
    int(number)
except ValueError:
    print("That's not a number..")
else:
    print(number)

You basically tell Python to check if the number provided by the user is an int. If it is, then the try block passes and the code in the else block runs. In this case, we print out the number.

If it's not an int, then we raise a ValueError. Which prevents your program from crashing, and enables you to print a message to your user letting them know what's going on.

Hopefully, this answers your question! You can find more information about Try/Except in the Python Basics Course.

https://teamtreehouse.com/library/expecting-exceptions

Pedro Cabral
Pedro Cabral
33,586 Points
Pedro Cabral
Pedro Cabral
33,586 Points 
if number.isdigit():
    number = int(number)
Abhinandan vig
Abhinandan vig
445 Points
Abhinandan vig
Abhinandan vig
445 Points

instead of using int, USE FLOAT eg:

number = float(number) --> in this case you don't have to worry about if user enter a floating point no and for string you can simply ask user in the first place that : print("Please only enter a no or decimal no !") Thanks ! Hope this helps !

Pedro Cabral
Pedro Cabral
33,586 Points

I think it's better to have a fool-proof solution. If you know an error might occur, you might as well catch it/handle it in the first place and take the burden away from the user. Imagine that you are using your OS and there is a message "oh btw, don't click here because you'll get an error", that wouldn't be very user friendly.