Ruby Mash相当于Python？

Question

in Ruby, there's this awesome library called a Mash which is a Hash but through clever use of missing_method can convert:

object['property']

to

object.property

This is really useful for mocks. Anyone know of a similar kind of thing in Python?

Answer 1

Is it absolutely necessary that you base this on a dict? Python objects can dynamically acquire attributes with very little extra plumbing:

>>> class C(object): pass
...
>>> z = C()
>>> z.blah = "xyzzy"
>>> dir(z)
['__class__', '__delattr__', '__dict__', ... '__weakref__', 'blah']

Answer 2

Is __getitem__ what you're looking for?

class C:
   def __init__(self):
      self.my_property = "Hello"

   def __getitem__(self, name):
      return getattr(self, name)

c = C()
print c['my_property']  # Prints "Hello"

or are you looking for the reverse of that, via __getattr__ ?

class D(dict):
   def __getattr__(self, name):
      return self[name]

d = D()
d['x'] = "Hello"
print d.x  # Prints "Hello"

( Edit : As Paul McGuire kindly points out in the comments, this code only demonstrates the bare bones of a full solution.)

Answer 3

Is it absolutely necessary that you base this on a dict?

Yes if you then want to treat it as a list of items, without abusing __dict__ .

The following is my old answer to the Mash question. It provides a default, the default may be a method or an object, if it's an object it will clone deeply ( not just hot-link) if it's used more than once.

And it exposes its simple key values as .key :

def Map(*args, **kwargs):
    value = kwargs.get('_default', None)
    if kwargs.has_key('_default'):  del kwargs['_default']

 # CONSIDER  You may want to look at the collections.defaultdict class.
 #      It takes in a factory function for default values.
 #
 # You can also implement your class by overriding the __missing__ method
 #      of the dict class, rather than overriding the __getitem__.
 #
 # Both were added in Python 2.5 according to the documentation.

    class _DefMap(dict):
        'But CONSIDER http://pypi.python.org/pypi/bunch/1.0.0 '

        def __init__(self, *a, **kw):
            dict.__init__(self, *a, **kw)
            self.__dict__ = self

        def __getitem__(self, key):

            if not self.has_key(key):

                if hasattr(value, '__call__'):
                    self[key] = value(key)
                else:
                    self[key] = copy.deepcopy(value)

            return dict.__getitem__(self, key)

    return _DefMap(*args, **kwargs)

Answer 4

Look here https://pypi.python.org/pypi/mash . Also you can convert dict to mash object.