python, deleting characters from a line, but leaving numbers and special symbols

Question

I need to delete all chars from a string, except numbers and special symbols. Exapmle "asdasd 289(222):310" should result in "289(222):310" . How do I do this ?

Answer 1

You could delete the letters,

>>> import re
>>> s = "asdasd 289(222):310"
>>> m = re.sub(r'[A-Za-z]+', r'', s)
>>> m
' 289(222):310'

If you want to delete spaces also then try the below code,

>>> m = re.sub(r'[A-Za-z ]+', r'', s)
>>> m
'289(222):310'

Answer 2

You could check each character to see if it is an alphabetic character.

>>> s = "asdasd 289(222):310"
>>> "".join(i for i in s if not i.isalpha())
' 289(222):310'

If you'd like to remove the leading and trailing whitespace, tack on a .strip()

>>> "".join(i for i in s if not i.isalpha()).strip()
'289(222):310'

The string class has methods isalpha() and isdigit() which are useful for things like this.

>>> '2'.isdigit()
True
>>> '2'.isalpha()
False
>>> 'a'.isdigit()
False
>>> 'a'.isalpha()
True

Answer 3

If, for whatever reason, speed is of the essence, the following code might help:

from string import maketrans
trans1 = maketrans("abcdefghijklmnopqrstuvwxyzABCDEFGHOJKLMNOPQRSTUVWXYZ", " "*52)
s = "asdasd 289(222):310"
m = s.translate(trans1).replace(" ", "")

Timings with ipython's %timeit show me 1.2 usec for this approach, 3.3 usec for the regex posted by Avinash Raj and 8sec for Cyber's method (on a Windows 8.1 64 bit Python 2.7.8 64 bit machine).

Using .strip insted of .replace is faster (~900 ns) but won't replace in between spaces.

Of course, timings do depend on the kind of data that will be processed.