Python Regular Expressions

gistfile1.txt

\   Used to drop the special meaning of character
    following it (discussed below)
[]  Represent a character class
^   Matches the beginning
$   Matches the end
.   Matches any character except newline
?   Matches zero or one occurrence.
|   Means OR (Matches with any of the characters
    separated by it.
*   Any number of occurrences (including 0 occurrences)
+   One ore more occurrences
{}  Indicate number of occurrences of a preceding RE 
    to match.
()  Enclose a group of REs

\d   Matches any decimal digit, this is equivalent
     to the set class [0-9].
\D   Matches any non-digit character.
\s   Matches any whitespace character.
\S   Matches any non-whitespace character
\w   Matches any alphanumeric character, this is
     equivalent to the class [a-zA-Z0-9_].
\W   Matches any non-alphanumeric character.