How to cast a int from string that contains not only numbers

Question

Casting a string is easy:

string1 = "12"
int1 = int(string1)

But what if I want to extract the int from

string1 = "12 pieces"

The cast should return 12. Is there a pythonic way to do that and ignore any chars that are not numbers?

Relevant: [Removing all non-numeric characters from string in Python](http://stackoverflow.com/questions/1249388/removing-all-non-numeric-characters-from-string-in-python). — Aurora0001, Oct 10 '16 at 18:11
I thing I just answered it myself: `[int(s) for s in string1.split() if s.isdigit()]` — Chris, Oct 10 '16 at 18:11
you can use `regex` or maybe you can split and do `try: int()` individually. — lycuid, Oct 10 '16 at 18:12
BTW: I would not really call this *casting*. This is simply calling the `int` constructor with a `str` argument. — zvone, Oct 10 '16 at 18:16

score 1 · Accepted Answer · answered Oct 10 '16 at 18:11

1

How about this?

>>> string1 = "12 pieces"
>>> y = int(''.join([x for x in string1 if x in '1234567890']))
>>> print(y)
12

or better yet:

>>> string1 = "12 pieces"
>>> y = int(''.join([x for x in string1 if x.isdigit() ]))
>>> print(y)
12

answered Oct 10 '16 at 18:11

Brian

1,988
1
14
29

score 1 · Answer 2 · answered Oct 10 '16 at 18:12

Is there a way to do that and ignore any chars that are not numbers?

Ignoring anything but a digit is, probably, not a good idea. What if a string contains "12 pieces 42", should it return 12, 1242, [12, 42], or raise an exception?

You may, instead, split the string and convert the first element to an int:

In [1]: int('12 pieces'.split()[0])
Out[1]: 12

score 1 · Answer 3 · answered Oct 10 '16 at 18:20

Assuming that the first part of the string is a number, one way to do this is to use a regex match:

import re

def strint(str):
    m=re.match("^[0-9]+", str)
    if m:
        return int(m.group(0))
    else:
        raise Exception("String does not start with a number")

The advantage of this approach is that even strings with just numbers can be cast easily, so you can use this function as a drop in replacement to int()

How to cast a int from string that contains not only numbers

3 Answers3