matching any character including newlines in a Python regex subexpression, not globally

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To match a newline, or “any symbol” without re.S/re.DOTALL, you may use any of the following:

  1. (?s). – the inline modifier group with s flag on sets a scope where all . patterns match any char including line break chars

  2. Any of the following work-arounds:

[\s\S]
[\w\W]
[\d\D]

The main idea is that the opposite shorthand classes inside a character class match any symbol there is in the input string.

Comparing it to (.|\s) and other variations with alternation, the character class solution is much more efficient as it involves much less backtracking (when used with a * or + quantifier). Compare the small example: it takes (?:.|\n)+ 45 steps to complete, and it takes [\s\S]+ just 2 steps.

See a Python demo where I am matching a line starting with 123 and up to the first occurrence of 3 at the start of a line and including the rest of that line:

import re
text = """abc
123
def
356
more text..."""
print( re.findall(r"^123(?s:.*?)^3.*", text, re.M) )
# => ['123\ndef\n356']
print( re.findall(r"^123[\w\W]*?^3.*", text, re.M) )
# => ['123\ndef\n356']

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