Extract email sub-strings from large document

Question

I have a very large .txt file with hundreds of thousands of email addresses scattered throughout. They all take the format:

......
         


        

Answer 1

Example : string if mail id has (a-z all lower and _ or any no.0-9), then below will be regex:

>>> str1 = "abcdef_12345@gmail.com"
>>> regex1 = "^[a-z0-9]+[\._]?[a-z0-9]+[@]\w+[.]\w{2,3}$"
>>> re_com = re.compile(regex1)
>>> re_match = re_com.search(str1)
>>> re_match
<_sre.SRE_Match object at 0x1063c9ac0>
>>> re_match.group(0)
'abcdef_12345@gmail.com'