how to iterate through files in a folder python

import os
directory = 'the/directory/you/want/to/use'

for filename in os.listdir(directory):
    if filename.endswith(".txt"):
      #do smth
      continue
    else:
    continue

import os

for filename in os.listdir(directory):
    if filename.endswith(".asm") or filename.endswith(".py"): 
         # print(os.path.join(directory, filename))
        continue
    else:
        continue

import os

for filename in os.listdir(directory):
    if filename.endswith(".asm") or filename.endswith(".py"): 
         # print(os.path.join(directory, filename))
        continue
    else:
        continue