Object-like attribute access for nested dictionary

The following class would let you do what you want (works in Python 2 & 3):

class AttrDict(dict):
    """ Dictionary subclass whose entries can be accessed by attributes (as well
        as normally).

    >>> obj = AttrDict()
    >>> obj['test'] = 'hi'
    >>> print obj.test
    hi
    >>> del obj.test
    >>> obj.test = 'bye'
    >>> print obj['test']
    bye
    >>> print len(obj)
    1
    >>> obj.clear()
    >>> print len(obj)
    0
    """
    def __init__(self, *args, **kwargs):
        super(AttrDict, self).__init__(*args, **kwargs)
        self.__dict__ = self

    @classmethod
    def from_nested_dicts(cls, data):
        """ Construct nested AttrDicts from nested dictionaries. """
        if not isinstance(data, dict):
            return data
        else:
            return cls({key: cls.from_nested_dicts(data[key]) for key in data})


if __name__ == '__main__':

    data = {
        "a": "aval",
        "b": {
            "b1": {
                "b2b": "b2bval",
                "b2a": {
                    "b3a": "b3aval",
                    "b3b": "b3bval"
                }
            }
        }
    }

    data1 = AttrDict.from_nested_dicts(data)
    print(data1.b.b1.b2a.b3b)  # -> b3bval

Building on @martineau's excellent answer, you can make the AttrDict class to work on nested dictionaries without explicitly calling the from_nested_dict() function:

class AttrDict(dict):
""" Dictionary subclass whose entries can be accessed by attributes
    (as well as normally).
"""
def __init__(self, *args, **kwargs):
    def from_nested_dict(data):
        """ Construct nested AttrDicts from nested dictionaries. """
        if not isinstance(data, dict):
            return data
        else:
            return AttrDict({key: from_nested_dict(data[key])
                                for key in data})

    super(AttrDict, self).__init__(*args, **kwargs)
    self.__dict__ = self

    for key in self.keys():
        self[key] = from_nested_dict(self[key])

Try Dotsi or EasyDict. They both support dot-notation for nested dicts.

>>> import dotsi
>>> data = dotsi.fy({'a': 'aval', 'b': {'b1':{'b2a':{'b3a':'b3aval','b3b':'b3bval'},'b2b':'b2bval'}} })
>>> print(data.b.b1.b2a.b3b)
b3bval
>>> 

In addition to dicts-within-dicts, Dotsi also supports dicts-within-lists-within-dicts.
Note: I'm Dotsi's author.