Dictionary subclasses supporting dot access for keys.

structures.py

"""Dictionary subclasses supporting dot access for keys."""

__all__ = ['AccessDict', 'SafeAccessDict']
__author__ = 'Brad Solomon <bsolomon@protonmail.com>'


class AccessDict(dict):
    """Dictionary with dot access, setting, and deletion of values.

    Otherwise, behaves the same.  (KeyError is still possible.)

    >>> b = AccessDict(a=1, b=2, c={'f': False, 't': True})
    >>> b.a
    1
    >>> type(b.c)
    <class 'AccessDict'>
    >>> b.d = 5
    >>> b
    {'a': 1, 'b': 2, 'c': {'f': False, 't': True}, 'd': 5}
    """

    # TODO: __str__/__repr__

    _check = dir({})
    def __init__(self, *args, **kwargs):
        for k in kwargs:
            if k in self._check:
                raise ValueError('You are attempting to use a key with'
                                 ' a name that is already\n an attribute'
                                 ' of a dictionary instance: `%s`' % k)
        self.update(*args, **kwargs)

    # `__getitem__()` and `__setitem__()` don't need to be touched.
    # For differences between `__getattr__()` and `__getattribute__()`:
    # https://docs.python.org/3/reference/datamodel.html

    def __getattr__(self, key):
        val = dict.__getitem__(self, key)
        # Do not use `isintance` -- it will catch inheritance
        # when we don't want it to.
        return AccessDict(val) if type(val) is dict else val

    __setattr__ = dict.__setitem__
    __delattr__ = dict.__delitem__

    # This is done by scikit-learn's `Bunch` class; not sure what
    # the intent is...
    #
    # def __dir__(self):
    #     return self.keys()

    def __setstate__(self, state):
        # https://github.com/scikit-learn/scikit-learn/issues/6196
        pass


class SafeAccessDict(AccessDict):
    """Dictionary with dot access, setting, and deletion of values.

    Another key feature is item access defaults to None rather
    than raising KeyError.

    >>> s = SafeAccessDict(a=1, b=2, c={'f': False, 't': True})
    >>> s.a
    1
    >>> type(s.c)
    <class 'SafeAccessDict'>
    >>> s.d = 5
    >>> s
    {'a': 1, 'b': 2, 'c': {'f': False, 't': True}, 'd': 5}
    >>> s.c.f
    False

    Be careful with nested access.  The get() -> default feature is
    *only* valid if the nested item is a dictionary/subclass thereof.
    >>> sb.c.f.a
    AttributeError: 'bool' object has no attribute 'a'
    """

    def __getattr__(self, key):
        val = dict.get(self, key)
        return SafeAccessDict(val) if type(val) is dict else val