os.walk() usage

[rbt]

I'm trying to write very small, modular code as functions to break up a 
big monolithic script that does a file system search for particular 
strings. The script works well, but it's not easy to maintain or add 
features to.

I'd like to have a function that builds a list of files with os.walk() 
and then have other functions accept that list as a parameter and modify 
it as needed. For example, if the user has specified that certain files 
and folders be excluded from the walk, I'd like to have functions like this:

def build_list(path):
     fs_list = os.walk(path)
     return fs_list

def skip_files(fs_list):
     remove files
     return fs_list

def skip_dirs(fs_list):
     remove dirs
     return fs_list

def search(fs_list):
     pass

The problem I'm encountering is passing the list to other functions. 
It's almost as if each function needs to build the list itself (walk the 
filesystem)... which gets in the way of what I was asked to do (break 
this thing up into modular, maintainable pieces).

Any tips on this?

Thanks