Returns full filepath if the file is in path or a subdirectory.

def find_file(path, filename, max_depth=5):
  """Returns full filepath if the file is in path or a subdirectory."""
  for root, dirs, files in os.walk(path):
    if filename in files:
      return os.path.join(root, filename)

    # Don't search past max_depth
    depth = root[len(path) + 1:].count(os.sep)
    if depth > max_depth:
      del dirs[:]  # Clear dirs
  return None