Exception Handling, function attempting to convert a string into an integer

Question

I am trying to write a function which turns a string into an integer, with an exception to catch anything which is not a digit and return a SyntaxError. The try here should take a string and return an integer if all characters in the string are digits. An example value of (sti) would be 12a34.

def string2int(sti):
    try:
        int(float(sti))
        if sti.isdigit():
            return sti
    except Exception, e:
        raise SyntaxError('not an integer')

Trying to iron it out in a python visualizer gives me an attribute error on line 4: AttributeError: 'float' object has no attribute 'isdigit'

There is an all_digits function I can use that takes a string and returns True if all the characters of the string are digits and False otherwise, but I haven't been able to get the try to work using that either.

How can I write this so that if the string does represent a positive integer then that integer is returned?

Ori Seri · Accepted Answer · 2014-04-05 11:59:59Z

1

def string2int(sti):
    try:
        return int(sti)
    except ValueError:
        raise SyntaxError('not an integer')

Or:

def string2int(sti):
    if sti.isdigit():
        return int(sti)
    else:
        raise SyntaxError('not an integer')

edited Apr 5, 2014 at 11:59

answered Apr 5, 2014 at 11:43

Ori Seri

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1 Comment

exclamationmark1 Over a year ago

Both of these work. I'm sure I tried many almost identical things, something about the try: except: must have been throwing me off.. Thanks for the correction!

Mohsen Kamrani · Accepted Answer · 2014-04-05 12:00:29Z

0

In your function if sti is an integer, this should simply work, but just for regular integers like 123 not even "+1" or "1e2":

def string2int(sti):
    try:
        if sti.isdigit():
            return sti

So you can use regular expressions:

import re
matchInt = re.match("^\+?[0-9]+([eE][0-9]+)?$",sti)
if matchInt:
    return sti

This regular expression matches against all (positive) integers shown regularly or in scientific notation.

edited Apr 5, 2014 at 12:00

answered Apr 5, 2014 at 11:42

Mohsen Kamrani

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