Cleanest way to obtain the numeric prefix of a string

Question

What is the cleanest way to obtain the numeric prefix of a string in Python?

By "clean" I mean simple, short, readable. I couldn't care less about performance, and I suppose that it is hardly measurable in Python anyway.

For example:

Given the string '123abc456def', what is the cleanest way to obtain the string '123'?

The code below obtains '123456':

input = '123abc456def' output = ''.join(c for c in input if c in '0123456789') 

So I am basically looking for some way to replace the if with a while.

Answer 1

You can use itertools.takewhile which will iterate over your string (the iterable argument) until it encounters the first item which returns False (by passing to predictor function):

>>> from itertools import takewhile >>> input = '123abc456def' >>> ''.join(takewhile(str.isdigit, input)) '123'