Python - Regular Expression (called REs, or regexes, or regex patterns)

About

The regexp in Python have matching operations similar to those found in Perl.

the backslash character ('\') indicate special forms or allow special characters
for example, to match a literal backslash, one might have to write '\\\\' as the pattern string, because the regular expression must be \\, and each backslash must be expressed as
inside a regular Python string literal.
backslashes are not handled in any special way in a string literal prefixed with 'r'. So r“\n” is a two-character string containing '\' and 'n', while “\n” is a one-character string containing a newline.

'^(\S+) (\S+) (\S+) \[([\w:/]+\s[+\-]\d{4})\] "(\S+) (\S+)\s*(\S*)" (\d{3}) (\S+)'

127.0.0.1 - - [24/Jul/1973:08:32:01 -0400] "GET /images/gerardnico.gif HTTP/1.0" 200 2564