from functools import partial

def list_files():
  for fn in ["example.txt", "data.txt"]:
    def func(fn):
        return "sample contents of %s" % fn
    yield fn, partial(func, fn)

for fn, body in list(list_files()):
  if fn.endswith('.txt'):
    print body()

sample contents of example.txt
sample contents of data.txt