Is there a function that can test if a path is in a directory or one of its sub-directory (recursively)?

[Peng Yu]

I looked though the os.path manual. I don't find a function that can
test if a path is in a directory or its sub-directory (recursively).

For example, /a/b/c/d is in /a its sub-directory (recursively). Could
somebody let me know if such function is available somewhere?