zomg.py

import os
import sys

def foo(dirname, dirtest, fileact):
    for c in os.listdir(dirname):
        cc = os.path.join(dirname, c)
        if os.path.isdir(cc) and dirtest(c):
            foo(cc, dirtest, fileact)
        elif os.path.isfile(cc):
            fileact(cc)

foo(".",
    lambda x: len(x) > 0 and x[0] != '.' and "tests" != x[:len("tests")],
    lambda x: sys.stdout.write("{}\n".format(x))
)

# Or, using a Functor

class WalkFunctor:
    def __init__(self, dirtest, fileact):
        self.dirtest = dirtest
        self.fileact = fileact

    def __call__(self,dirname):
        for c in os.listdir(dirname):
            cc = os.path.join(dirname, c)
            if os.path.isdir(cc) and self.dirtest(c):
                self(cc)
            elif os.path.isfile(cc):
                self.fileact(cc)

f = WalkFunctor(
    lambda x: len(x) > 0 and x[0] != '.' and "tests" != x[:len("tests")],
    lambda x: sys.stdout.write("{}\n".format(x))
)
f(".")