Question

im writing a function to return a random file in a directory, also – i want to be able to match a substring in the file name.

def get_rand_file(folder, match=None):
    if match == None:
        return random.choice(os.listdir(folder))
    else:
        matching = []
        for s in os.listdir(folder):
            if match in s:
                matching.append(s)
        return random.choice(matching)

this code will work, but i am working with LOTS of files and this code takes a while, i tried doing it with list comprehension and mapping and i couldn’t make it work. any suggestions?

Answer 1

def get_rand_file(folder, match=None):
   if match == None:
       return random.choice(os.listdir(folder))
   else:
       return random.choice([s for s in os.listdir(folder) if match in s])

Documentation on list comprehensions :

http://docs.python.org/tutorial/datastructures.html#list-comprehensions