python - Most efficient way to remove non-numeric list entries

Question

I'm looking to 'clean' a list by excluding any items which contain characters other than 0-9, and wondering if there's a more efficient way than e.g.

import re
invalid = re.compile('[^0-9]')    
ls = ['1a', 'b3', '1']
cleaned = [i for i in ls if not invalid.search(i)]
print cleaned
>> ['1']

As I'm going to be operating on large-ish lists (5k items) of long strings (15 chars).

Answer 1

Anything wrong with the string method isdigit ?

>>> ls = ['1a', 'b3', '1']
>>> cleaned = [ x for x in ls if x.isdigit() ]
>>> cleaned
['1']
>>>