如何用正则表达式提取键子字符串和“ /”之间的字符串？

Question

I have a string that's

/path/to/file?_subject_ID_SOMEOTHERSTRING

the path/to/file part changes depends on situation, and subject_ID is always there. I try to write a regex that extract only file part of the string. Using ?subject_ID is definite, but I don't know how to safely get the file

My current regex looks like (.*[\\/]).*\\?_subject_ID

url = '/path/to/file?_subject_ID_SOMEOTHERSTRING'
file_re = re.compile('(.*[\/]).*\?_subject_ID')
file_re.search(url)

this will find the right string, but I still can't extract the file name

printing _.group(1) will get me /path/to/ . What's the next step that gets me the actual file name?

Answer 1

As for your '(.*[\\/]).*\\?_subject_ID' regex approach, you just need to add a capturing group around the second .* . You could use r'(.*/)(.*)\\?_subject_ID' (then, there will be .group(1) and .group(2) parts captured), but it is not the most appropriate way to parse URLs in Python.

You may use the non-regex approach here, here is a snippet showing how to leverage urlparse and os.path to parse the URL like yours:

import urlparse
path = urlparse.urlparse('/path/to/file?_subject_ID_SOMEOTHERSTRING').path
import os.path
print(os.path.split(path)[1]) # => file
print(os.path.split(path)[0]) # => /path/to

See the IDEONE demo

Answer 2

It's pretty simple, really. Just match a / before and ?subject_ID after:

([^/?]*)\?subject_ID

The [^/?]* (as opposed to .* ) is because otherwise it'd match the part before, too. The ? in the character class

If you want to get both the path and the file, you can do much the same thing, but also grab the part before the / :

([^?]*)([^/?]*)\?subject_ID

It's basically the same as the one before but with the first bit captured instead of ignored.