[Tutor] Regex ^$ not behaving as expected
edmundb at talktalk.net
Thu Dec 8 07:45:31 EST 2016
I am new to Python and trying to get to grips with the re regex module.
I’m running Python 3.4 under Debian Jessie with a Cinnamon desktop.
My understanding is that when the re.M flag is raised, |^| will match at
the beginning of the string and also at the beginning of each line
within the string immediately following each newline \n. Similarly, |$
|matches both at the end of the whole string and at the end of each line
immediately preceding the \n.
However I don’t seem to be able to get re.sub (for instance) to behave
in this way. Both ^ and $ seem only to match the beginning and end of
the string and not the individual lines within it. The session below
hopefully demonstrates my confusion.
Python 3.4.2 (default, Oct 8 2014, 10:45:20)
[GCC 4.9.1] on linux
Type "copyright", "credits" or "license()" for more information.
>>> import re
>>> s = "AAAcBBB\nAAAdBBB"
>>> print(re.sub(r'^.+?c', "X", s))
>>> print(re.sub(r'^.+?d', "X", s, re.M))
>>> print(re.sub(r'^.+?d', "X", s, re.M, re.S))
>>> print(re.sub(r'd.+?$', "X", s))
>>> print(re.sub(r'c.+?$', "X", s, re.M))
>>> print(re.sub(r'c.+?$', "X", s, re.M, re.S))
What am I doing wrong? Thank you
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