How to check if string is (int or float) in Python 2.7

Question

I know similar questions have been asked and answered before like here: How do I check if a string is a number (float) in Python?

However, it does not provide the answer I'm looking for. What I'm trying to do is this:

def main():
    print "enter a number"
    choice = raw_input("> ")
    # At this point, I want to evaluate whether choice is a number.
    # I don't care if it's an int or float, I will accept either.

    # If it's a number (int or float), print "You have entered a number."
    # Else, print "That's not a number."
main()

Answers to most of the questions suggest using try..except, but this only allows me to evaluate int or floats exclusively, i.e

def is_number(s):
    try:
        float(choice)
        return True
    except ValueError:
        return False

If I use this code, int values will end up in the exception.

Other methods I've seen include str.isdigit. However, this returns True for int and false for float.

`float('123')` returns `123.0` and doesn't give you `ValueError`. So your function works fine. — Remi Guan, Dec 22 '15 at 22:38
*"If I use this code, int values will end up in the exception"* - nope. Please actually try these things before asking. — jonrsharpe, Dec 22 '15 at 22:38
Thanks for the clarification guys. I did try that method before asking this but I couldn't get it to work. Must have made a mistake somewhere. Either way, it works now just like you guys mentioned. Thanks!! — wcj, Dec 22 '15 at 22:56
Does this answer your question: [Checking whether a variable is an integer or not](http://stackoverflow.com/questions/3501382/checking-whether-a-variable-is-an-integer-or-not) Thomas — Thomas, Dec 22 '15 at 23:22

score 4 · Answer 1 · answered Dec 22 '15 at 22:38

4

In your case it is enough to simply check whether the input can be converted to a float in a try/except block. The conversion will be successful for any string that could have been converted to an integer as well.

answered Dec 22 '15 at 22:38

timgeb

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score 2 · Answer 2 · answered Dec 22 '15 at 22:55

the function you used should be converting int and float values in the form of a string to a float successfully. for some reason you want to specifically want to find weather it is an int or float consider this change.

def is_int_or_float(s):
    ''' return 1 for int, 2 for float, -1 for not a number'''
    try:
        float(s)

        return 1 if s.count('.')==0 else 2
    except ValueError:
        return -1
print is_int_or_float('12')
print is_int_or_float('12.3')
print is_int_or_float('ads')

here is the result

python test.py
1
2
-1

score 1 · Answer 3 · answered May 10 '16 at 12:04

1

You can write your own function,

def is_int_or_float(a):
    if type(a) is int or type(a) is float:
        return True
    else:
       return False

You can write even more compact program. Between please do that yourself.

Thanks!

answered May 10 '16 at 12:04

Annapoornima Koppad

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score 0 · Answer 4 · answered Dec 22 '15 at 23:39

0

You can use the isstance() method and literal_eval

example

from ast import literal_eval

   isinstance(literal_eval('3'),int)

returns

True

or you can use json.

import json

isinstance(json.loads('3'),int)

return

True

answered Dec 22 '15 at 23:39

repzero

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score 0 · Answer 5 · answered Nov 07 '17 at 16:24

0

I know this is old, but I did a simple check:

    var = 3

    try: #if it can be converted to a float, it's true
        float(var) 
    except: # it it can't be converted to a float, it's false
        do stuff with the var

answered Nov 07 '17 at 16:24

Mike

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How to check if string is (int or float) in Python 2.7

5 Answers5