How to get a specific parent of a path by its name?

Question

I have a function that returns the full path of a specific parent that I look for by a constant name. I am currently using os.path and strings for paths so right now this is done with regular-expressions.

What I want is for example for a constant parent = d to be able to get:

/a/b/c/d/e      -->  /a/b/c/d
/a/b/c/d/e/f    -->  /a/b/c/d
/root/a/b/c/d/e -->  /root/a/b/c/d

Note: as the example shows I don't want to rely on any fixed position from both sides.

I have tried 2 ways but both feels a bit clunky:

1. Use the parts in order to find the correct parents element:

   >>> path = "/a/b/c/d/e/f"
   >>> parts = Path(path).parts
   >>> parent_index = len(parts) - 1 - parts.index('d') - 1
   >>> Path(path).parents[parent_index]
   PosixPath('/a/b/c/d')
   

2. Use the parts and concatenate the relevant ones:

   >>> path = "/root/a/b/c/d/e"
   >>> parts = Path(path).parts
   >>> Path(*parts[:parts.index('d')+1])
   PosixPath('/root/a/b/c/d')
   

I would say that the second one seems reasonable, but still, my question is: Is there a more direct, pythonic way to achieve this? The repeated indexing and slicing of the parents feels inefficient and quite confusing.

---

P.S. In case the part is not present in the path it is enough to raise an exception or any indicator (right now I wrap the code with index above with a try/except).

Answer 1

You can use a while loop instead to keep searching backwards for a parent of the given name:

path = Path("/a/b/c/d/e/f")
while path.name != 'd':
    path = path.parent
    assert path.name, 'No parent found with the given name'
print(path)

This outputs:

/a/b/c/d