Remove everything but leave numbers and dots

Question

This code is designed to remove everything but leave numbers

a = "1.1.1.1"
b = re.sub('[^0-9]', '', a)

but i want to preserve dots as well.

Answer 1

Try out

a = 1.1.1.1
b = re.sub('[^\d\.]', '', a)

instead. 0-9 can be replaced with \\d because that matches all numerical characters, and the \\. is necessary because the . character is a wildcard.

Answer 2

Not using regular expression:

>>> ''.join(c for c in a if c.isdigit() or c == '.')
'1.1.1.1'
>>> a = 'hello.1.number'
>>> ''.join(c for c in a if c.isdigit() or c == '.')
'.1.'

Answer 3

>>> a='1.1.1.1'
>>> b = re.sub('[^0-9\.]', '', a)
>>> b
'1.1.1.1'
>>> a='comp.languages.python'
>>> b = re.sub('[^0-9.]', '', a)
>>> b
'..'

The [] means match only these characters.

The [^] means match all characters EXCEPT these characters.

0-9 is 0123456789

. is . but be careful with . because outside [] it is often used to match any single character