Regular Expressions using Python

From re docs:

Ranges of characters can be indicated by giving two characters and separating them by a '-', for example [a-z] will match any lowercase ASCII letter, [0-5][0-9] will match all the two-digits numbers from 00 to 59, and [0-9A-Fa-f] will match any hexadecimal digit. If - is escaped (e.g. [a-z]) or if it’s placed as the first or last character (e.g. [-a] or [a-]), it will match a literal '-'. [emphasis added]

It looks like you are trying to match a literal -, so place it as the first character of the range, e.g. [-xxx]:

pattern = re.compile(r'\b([a-zA-Z])([-\w._+]+)@([-\w.]+)([a-zA-Z])\b')

Test:

>>> import re
>>> pat = r"\b([a-zA-Z])([-\w._+]+)@([-\w.]+)([a-zA-Z])\b"
>>> old_pattern = re.compile(r'\b([a-zA-Z])([\w.-_+]+)@([\w.-]+)([a-zA-Z])\b')
>>> new_pattern = re.compile(r'\b([a-zA-Z])([-\w._+]+)@([-\w.]+)([a-zA-Z])\b')
>>> old_pattern.search('[email protected]')
<re.Match object; span=(21, 35), match='[email protected]'>
>>> new_pattern.search('[email protected]')
<re.Match object; span=(0, 35), match='[email protected]'>

Welcome to the wonderful world of regular expressions, where the tiniest of changes can result in totally unexpected outcomes.

To start, let's analyze the regex pattern you have:

r'\b([a-zA-Z])([\w.-_+]+)@([\w.-]+)([a-zA-Z])\b'

• \b is a correct choice, since you want items which are there own word. Be careful though, since this won't include the beginning or end of a string.
• ([a-zA-Z]) if your first capture group. You can replace with the simpler ([A-z])
• ([\w.-_+]+) is your second capture group. It will capture:
  • \w any word character (redundant)
  • . will not necessarily capture the period character, instead, is capturing "any" character
  • - will not capture the dash character, instead, will capture a range of characters
  • _ will indeed capture underscore characters – but in this case, it's being referenced as the end of a range
  • + will not capture plus characters, rather, will get "1 or more" characters from a group or range.

... I'll stop here, since the rest is more or less similar...

You'll want to replace your regex with the following:

r'\b([A-z0-9\-\+]+@[A-z\-\+]+\.[A-z]{3})\b'

• There is only one capture group, since we want entire email addresses.
• Email addresses (here) are allowed to contain:
  • Before the at symbol: [A-z0-9\-\+]+ all alpha-numeric characters as well as '-' and '+' characters (as denoted by the escaped characters \- and \+
  • Following the at symbol, a domain name [A-z\-\+] with alpha characters and escaped chars
  • Followed by a domain extension \.[A-z]{3} Ex: .org

Next, you can refactor your code to the following:

import re

pattern = re.compile(r'\b([A-z0-9\-\+]+@[A-z\-\+]+\.[A-z]{3})\b')
match = pattern.search(s)

if match:
   email = match.group()
else:
   email = None