Prefer closures over classes keeping state

closures_ftw.py

# Bad
class Join(object):
  """
  >>> join_by_commas = Join(',')
  >>> join_by_commas(['o', 'm', 'g'])
  'o,m,g'
  """

    def __init__(self, separator=u' '):
        self.separator = separator

    def __call__(self, values):
        return self.separator.join(values)
        
# Good
def join(separator=u' '):
  """
  >>> join_by_commas = join(',')
  >>> join_by_commas(['f', 't', 'w'])
  'f,t,w'
  """
    def inner_join(values):
        return separator.join(values)
    return inner_join