import re
+ matching 1 or more of the preceding letter.
a+ "a", "aa", "aaa"
* matching 0 or more of the preceding letter.
a* "", "a", "aa"
? matching 0 or 1 of the preceding letter.
a? "", "a"
a{m} exactly m copies of the preceding letter
a{3} "aaa"
a{m,n} matching m to n copies of the preceding letter, attempting to match as many repetitions as possible. omitting n mean infinite upper bound.
a{m,n}? matching m to n copies of the preceding letter, attempting to match as few repetitions as possible. omitting n mean infinite upper bound.
\d decimal digit [0-9]
\w alphanumeric characters [a-zA-Z0-9_]
"a", "b", "1", "2", "_"
\W any character which is not alphanumeric characters [^a-zA-Z0-9_]
\s whitespace characters [ \t\n\r\f\v]
\S any character which is not a whitespace character [^ \t\n\r\f\v]
\. "." letter
. matches any character except a newline