details two optional chaining methods

optional_chaining.py

empty = None
deep = dict(a=dict(b='c'))


def chain_optional(func, default_value=None):
  try:
    return func()
  except AttributeError:
    return default_value
  except TypeError:
    return default_value

assert chain_optional(lambda: empty.test) is None
assert chain_optional(lambda: deep['a']['b']) is 'c'


EMPTY_IDENTIFIER = object()
class Optional(object):
  def __init__(self, item=EMPTY_IDENTIFIER, default_value=None):
      self.item = item
      self.default_value = None

  def __getattr__(self, name):
      if isinstance(self.item, dict):
        return Optional(self.item.get(name, EMPTY_IDENTIFIER))
      elif hasattr(self.item, name):
        return Optional(getattr(self.item, name))
      else:
        return Optional()

  def __call__(self):
    return self.default_value if self.item is EMPTY_IDENTIFIER else self.item

assert Optional(empty).test() is None
assert Optional(deep).a.b() is 'c'
assert Optional(deep).a.b.c.d() is None