Issue 36206: re.match() not matching escaped hyphens (original) (raw)

Issue36206

Created on 2019-03-06 02:39 by lprice, last changed 2022-04-11 14:59 by admin. This issue is now closed.

Messages (3)
msg337272 - (view)	Author: Lottie Price (lprice)	Date: 2019-03-06 02:39
Problem: re.match("\\-", "\\-") returns None. I expected a match. Context: I have some random text strings I want to match against. I'm using re.escape() to ensure that the text characters are not interpreted as special characters: re.match(re.escape("-"), re.escape("-")) As a result, strings with hyphens are coming back as above, and are not matching.
msg337274 - (view)	Author: Josh Rosenberg (josh.r) *	Date: 2019-03-06 03:45
"\\-" is equivalent to the raw string r"\-" (that it, it has one backslash, followed by a hyphen). \X (where X is any ASCII non-letter, non-digit) matches the character itself (the escape does nothing except ensure the punctuation doesn't have any special regex meaning). So your pattern is equivalent to "-". Since re.match has an implicit anchor at the beginning of the string (making it roughly like "^-"), the string "\-" doesn't match. Use raw strings consistently for your regular expressions to reduce the number of rounds of deescaping. re.match(r"\\-", "\\-") works as you expected.
msg337275 - (view)	Author: Steven D'Aprano (steven.daprano) *	Date: 2019-03-06 03:54
You don't escape the text you are searching. Try this: py> re.match(re.escape('-'), "-") <_sre.SRE_Match object; span=(0, 1), match='-'> py> re.match(re.escape('a-c'), "a-c") <_sre.SRE_Match object; span=(0, 3), match='a-c'>