Validating for a data type in Python

Question

I wanted to validate the data type as int or float in this simple code, I've gone wrong somewhere and the error message "Enter an integer!" shows up no matter what. I have already tried putting a == instead of != and putting all other statements after the if, but the problem persists.

def menuLoop():

    marks = input("Please Enter the Obtained Marks: ")
    if type(marks) != int or float:
        print("Enter an integer!")
        menuLoop()

    else:
        if int(marks) >= 75:
            print("A")
            menuLoop()
        elif marks >= 60:
            print("B")
            menuLoop()
        elif marks >= 35:
            print("C")
            menuLoop()
        elif marks < 35:
            print("D")
            menuLoop()



menuLoop()

Also, note that the function recursively calling itself until it gets a valid answer can lead to all sorts of problems. Use a loop instead. — Thierry Lathuille, Feb 03 '19 at 12:27
You could have simply figured out what the problem is by using python interpreter, just execute `type(mark)`. And you would be able to find out what was the problem. Try some debugging first before posting question here. — letsintegreat, Feb 03 '19 at 12:35

letsintegreat · Answer 1 · 2019-02-04T03:53:26.800

In Python, the problem is that the input(), by default, is neither int nor float, that is a string.

If you want to check if the input is in the form of int, you can do that like this:

try:
    # mark is going to convert in int, if it can.
    # otherwise, it will throw a ValueError
    mark = int(mark)
except ValueError:
    # Handle the exception
    print 'Please enter an integer'
    menuLoop()

The function int() raises a ValueError, if the given parameter is not convertible in int. So, after catching that ValueError, we can show a message that to enter an integer value, like I've shown above.

score 0 · Answer 2 · answered Feb 03 '19 at 12:27

This is a little tricky, but it will fix the logic, change your condition to:

if not marks.replace('.','',1).isdigit():
    print("Enter an integer!")
    menuLoop()

It will go inside the if if user inputs int or float.

.replace('.','',1) will replace only one . then check that all of the other characters are number or not.

Validating for a data type in Python

2 Answers2