Question

strings = ["1 asdf 2", "25etrth", "2234342 awefiasd"] #and so on

Which is the easiest way to get [1, 25, 2234342]?

How can this be done without a regex module or expression like (^[0-9]+)?

Answer 1

One could write a helper function to extract the prefix:

def numeric_prefix(s):
    n = 0
    for c in s:
        if not c.isdigit():
            return n
        else:
            n = n * 10 + int(c)
    return n

Example usage:

>>> strings = ["1asdf", "25etrth", "2234342 awefiasd"]
>>> [numeric_prefix(s) for s in strings]
[1, 25, 2234342]

Note that this will produce correct output (zero) when the input string does not have a numeric prefix (as in the case of empty string).

Working from Mikel’s solution, one could write a more concise definition of numeric_prefix:

import itertools

def numeric_prefix(s):
    n = ''.join(itertools.takewhile(lambda c: c.isdigit(), s))
    return int(n) if n else 0