[python] Regular expression to match a dot

Was wondering what the best way is to match "test.this" from "blah blah blah [email protected] blah blah" is? Using Python.

I've tried re.split(r"\b\w.\w@")

In your regex you need to escape the dot "\." or use it inside a character class "[.]", as it is a meta-character in regex, which matches any character.

Also, you need \w+ instead of \w to match one or more word characters.

Now, if you want the test.this content, then split is not what you need. split will split your string around the test.this. For example:

>>> re.split(r"\b\w+\.\w+@", s)
['blah blah blah ', 'gmail.com blah blah']

You can use re.findall:

>>> re.findall(r'\w+[.]\w+(?=@)', s)   # look ahead
['test.this']
>>> re.findall(r'(\w+[.]\w+)@', s)     # capture group
['test.this']

This expression,

(?<=\s|^)[^.\s]+\.[^.\s]+(?=@)

might also work OK for those specific types of input strings.

Demo

Test

import re

expression = r'(?<=^|\s)[^.\s]+\.[^.\s]+(?=@)'
string = '''
blah blah blah [email protected] blah blah
blah blah blah test.this @gmail.com blah blah
blah blah blah [email protected] blah blah
'''

matches = re.findall(expression, string)

print(matches)

Output

['test.this']

If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com. If you'd like, you can also watch in this link, how it would match against some sample inputs.

A . in regex is a metacharacter, it is used to match any character. To match a literal dot, you need to escape it, so \.

In javascript you have to use \. to match a dot.

Example

"blah.tests.zibri.org".match('test\\..*')
null

and

"blah.test.zibri.org".match('test\\..*')
["test.zibri.org", index: 5, input: "blah.test.zibri.org", groups: undefined]

"In the default mode, Dot (.) matches any character except a newline. If the DOTALL flag has been specified, this matches any character including a newline." (python Doc)

So, if you want to evaluate dot literaly, I think you should put it in square brackets:

>>> p = re.compile(r'\b(\w+[.]\w+)')
>>> resp = p.search("blah blah blah [email protected] blah blah")
>>> resp.group()
'test.this'

to escape non-alphanumeric characters of string variables, including dots, you could use re.escape:

import re

expression = 'whatever.v1.dfc'
escaped_expression = re.escape(expression)
print(escaped_expression)

output:

whatever\.v1\.dfc

you can use the escaped expression to find/match the string literally.