Python has special designations for character sets:
\d- any digit
\D- any non-numeric value
\s- whitespace character
\S- all except whitespace characters
\w- any letter, digit or underline character
\W- all except letter, digit or underline character
These are not all character sets that support Python. See documentation for details.
Character sets allow you to write shorter expressions without having to list all necessary characters. For example, get time from log file string:
In : log = '*Jul 7 06:15:18.695: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0/3, changed state to down' In : re.search('\d\d:\d\d:\d\d', log).group() Out: '06:15:18'
\d\d:\d\d:\d\d describes 3 pairs of numbers separated by colons.
Getting MAC address from log message:
In : log2 = 'Jun 3 14:39:05.941: %SW_MATM-4-MACFLAP_NOTIF: Host f03a.b216.7ad7 in vlan 10 is flapping between port Gi0/5 and port Gi0/15' In : re.search('\w\w\w\w\.\w\w\w\w\.\w\w\w\w', log2).group() Out: 'f03a.b216.7ad7'
\w\w\w\w\.\w\w\w\w\.\w\w\w\w describes 12 letters or digits that
are divided into three groups of four characters and separated by dot.
Symbol groups are very convenient, but for now it is necessary to manually specify a character repetition. The following subsection covers repetition symbols which will simplify description of expressions.