I have a string representing the full path to a file:
full_path = '/home/user/fold1/fold2/sub-fold/'
and I need to remove from this string its root path stored in a different variable:
root = '/home/user/fold1/'
The resulting path should thus look like:
new_path = 'fold2/sub-fold/'
The full path (and obviously the root path) keeps changing as my code runs through many files stored in many different locations.
This is the (non-existent) operation I'm after:
new_path = full_path - root
How can I do this?
You can either strip the beginning matching the length of the root (bgoldst's answer):
path[len(root):]
But then you would not notice if that beginning would not match the root you expect. If, for instance, you have /bla/foo as root and /bar/zap/fong/tang as file, you would get /fong/tang as a result, effectively cloaking the former bug. I would not suggest to do that.
Replacing the string root in the given path rigorously (Aprillion's) could replace later occurrences as well, effectively returning nonsense, as the comments pointed out.
I would suggest to replace the beginning of the string properly:
import re
result = re.sub(r'^' + re.escape(root), '', path)
This way you avoid both traps.
You might also want to consider just using os.path.relpath() which strips a given start from a path according to file system logic.
In any case you should consider how your program should behave in the case that the given root does not match the beginning of the path. The re solution I proposed will then just not change the given path. In most cases this will be a useful behavior but certainly not in all cases.