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, a

Answer 1

Here is my way:

output = input[:next((i for i,v in enumerate(input) if not v.isdigit()),None)]

Answer 2

This is the simplest way to extract a list of numbers from a string:

>>> import re
>>> input = '123abc456def'
>>> re.findall('\d+', s)
['123','456']

If you need a list of int's then you might use the following code:

   >>> map(int, re.findall('\d+', input ))
   [123,456]

And now you can access the first element [0] from the above list

Answer 3

Another regexp version strips away everything starting with the first non-digit:

import re
output = re.sub('\D.*', '', input)

Answer 4

input[:len(input) - len(input.lstrip("0123456789"))]

Answer 5

You could use regex

import re
initialNumber = re.match(r'(?P<number>\d+)', yourInput).group('number')

Answer 6

Simpler version (leaving the other answer as there's some interesting debate about which approach is better)

input[:-len(input.lstrip("0123456789"))]