python regular expression

Question

hi, well this is my problem, i'm working in a script (python) to find some files, i compare names of files against a regular expression pattern, now, i have to find files ended with a "~" (tilde), so i builded the next regex:

if re.match("~$", string_test):
    print "ok!"

well, python seems to not recognize the regex, i dont know why, i tried the same regex in other languages and it works perfectly, any idea??

PD: i read in a web that i have to insert

# -*- coding: utf-8 -*-

but doesn't help :( .

Thanks a lot, meanwhile i'm going to keep reading to see if a find something.

Answer 1

re.match() is only successful if the regular expression matches at the beginning of the input string. To search for any substring, use re.search() instead:

if re.search("~$", string_test):
    print "ok!"

Answer 2

Your regex will only match strings "~" and (believe it or not) "~\n".

You need re.match(r".*~$", whatever) ... that means zero or more of (anything except a newline) followed by a tilde followed by (end-of-string or a newline preceding the end of string).

In the unlikely event that a filename can include a newline, use the re.DOTALL flag and use \Z instead of $.

"worked" in other languages: you must have used a search function.

r at the beginning of a string constant means raw escapes e.g. '\n' is a newline but r'\n' is two characters, a backslash followed by n -- which can also be represented by '\n'. Raw escapes save a lot of \\ in regexes, one should use r"regex" automatically

BTW: in this case avoid the regex confusion ... use whatever.endswith('~')

Answer 3

For finding files, use glob instead,

import os
import glob

path = '/path/to/files'
os.chdir(path)
files = glob.glob('./*~')

print files

Answer 4

The correct regex and the glob solution have already been posted. Another option is to use the fnmatch module:

import fnmatch
if fnmatch.fnmatch(string_test, "*~"):
    print "ok!"

This is a tiny bit easier than using a regex. Note that all methods posted here are essentially equivalent: fnmatch is implemented using regular expressions, and glob in turn uses fnmatch.

Note that only in 2009 a patch was added to fnmatch (after six years!) that added support for file names with newlines.