Python Language Flags


Example

For some special cases we need to change the behavior of the Regular Expression, this is done using flags. Flags can be set in two ways, through the flags keyword or directly in the expression.

Flags keyword

Below an example for re.search but it works for most functions in the re module.

m = re.search("b", "ABC")  
m is None
# Out: True

m = re.search("b", "ABC", flags=re.IGNORECASE)
m.group()
# Out: 'B'

m = re.search("a.b", "A\nBC", flags=re.IGNORECASE) 
m is None
# Out: True

m = re.search("a.b", "A\nBC", flags=re.IGNORECASE|re.DOTALL) 
m.group()
# Out: 'A\nB'

Common Flags

FlagShort Description
re.IGNORECASE, re.IMakes the pattern ignore the case
re.DOTALL, re.SMakes . match everything including newlines
re.MULTILINE, re.MMakes ^ match the begin of a line and $ the end of a line
re.DEBUGTurns on debug information

For the complete list of all available flags check the docs

Inline flags

From the docs:

(?iLmsux) (One or more letters from the set 'i', 'L', 'm', 's', 'u', 'x'.)

The group matches the empty string; the letters set the corresponding flags: re.I (ignore case), re.L (locale dependent), re.M (multi-line), re.S (dot matches all), re.U (Unicode dependent), and re.X (verbose), for the entire regular expression. This is useful if you wish to include the flags as part of the regular expression, instead of passing a flag argument to the re.compile() function.

Note that the (?x) flag changes how the expression is parsed. It should be used first in the expression string, or after one or more whitespace characters. If there are non-whitespace characters before the flag, the results are undefined.