If a space in filename, hfy-list-files function error. For example:

$ mkdir /tmp/test 
$ cd /tmp/test
$ touch 'hello world.py'
$ touch hi.py
$ ls
hello world.py  hi.py

In Emacs:

(hfy-list-files "/tmp/test")
("hi.py" "hello" "world.py")

As shown above, "hello world.py" is split into two files.