What is the correct regex statement using re.search() to find and return a file extension in a string.
Such as:
(.+).(avi|rar|zip|txt)
I need it to search a string and if it contains any of those avi, rar, etc) return just that extension.
Thanks!
EDIT: should add that is needs to be case insensitive
the standard library is better ;)
>>> os.path.splitext('hello.py')
('hello', '.py')
You need:
(.)\.(avi|rar|zip|txt)$
Note the backslash to escape the dot. This will make it look for a literal dot rather than any character.
To make it case insensitive, use the RE.I flag in your search call.
re.search(r'(.)\.(avi|rar|zip|txt)$', string, re.I)
import re as RE to be able to find RE.I...
.\.(avi|rar|zip|txt)$: this will ensure that there's some character before the dot, and that the file extension is at the end of the string. This way you end up with the first match being the extension rather than the second one, and you don't end up keeping a match that you don't need.
RE.I instead of re.I)Short interactive run:
>>> import re
>>> pat="(.+)\.(avi|rar|zip|txt)"
>>> re.search(pat, "abcdefg.zip", re.IGNORECASE).groups()
('abcdefg', 'zip')
>>> re.search(pat, "abcdefg.ZIP", re.IGNORECASE).groups()
('abcdefg', 'ZIP')
>>>
r"(.+)\.(avi|rar|zip|txt)"(.+)[.](avi|rar|zip|txt)
Then the group 2 will be extension.
I have just written a blog about Regular Expression http://blogs.appframe.com/erikv/2010-09-23-Regular-Expression if you want to read more about this.
Since I think regex is evil...
def return_extension(filename):
'''(This functions assumes that filenames such as `.foo` have extension
`foo`.)
'''
tokens = filename.split('.')
return '' if len(tokens) == 1 else tokens[-1]
...I advocate simply parsing the filename.
If you know that the extension is at the very end of the string, this should work well:
.\.(avi|rar|zip|txt)$
The first bit will ensure that there's some character before the dot.
The $ specifies that the file extension is at the end of the string, i.e. the $ means "the string ends here". For gory details on this, including some edge cases with newlines that you should be aware of see the comment discussion for JoshD's answer, as well as the entry for $ in the docs.
So then the only entry in the match.groups() tuple, i.e. match.groups()[0], will be the extension itself.
split('\n') on a file listing from a file or pipeline), so it seems worth giving a specific solution for it. In this case I think it's actually better to use the $ because it's compatible with fileinput.input() without having to rstrip the lines first.\Z does the job reliably. Another way of looking at it is that $ is a perlish substitute for \n?\Z ... fileinput.input()? oh, yeah, I remember, Python crutch for awk tragics -- I stopped using it some time in 1998.
.avior do you want to check that a string ends with that? Asking another way, is the string general text "Fred sent me foo.rar today" or is it supposed to contain a file name or path whose extension you want to extract?