hbutils.collection.stacked

StackedMapping

class hbutils.collection.stacked.StackedMapping(*mps: collections.abc.Mapping)

Overview:

Stacked mapping data structure.

Multiple mapping-liked object (such as dict) can be stacked together and accessed like one mapping object.

Note

StackedMapping is readonly. The __setitem__ and __delitem__’s behaviour cannot be defined, because which dict to write or delete can not be determined.

Examples::

>>> from hbutils.collection import StackedMapping
>>>
>>> d1 = {'a': 1, 'b': 2}
>>> d2 = {'b': 3, 'c': 4, 'd': 5}
>>> d3 = {'c': 6, 'e': 7}
>>> s = StackedMapping(d1, d2, d3)  ## stack together, d3 > d2 > d1
>>>
>>> for key, value in s.items():  # __iter__
...     print(key, value)
a 1
b 3
c 6
d 5
e 7
>>> s['a']  # __getitem__, from d1['a']
1
>>> s['b']  # from d2['b'], d2 > d1
3
>>> s['c']  # from d3['c'], d3 > d2
6
>>> s['d']  # from d2['d']
5
>>> s['e']  # from d3['e']
7
>>> 'c' in s  # __contains__
True
>>> 'f' in s  # 'f' not found in neither d1, d2 nor d3
False
>>> s == {'a': 1, 'b': 3, 'c': 6, 'd': 5, 'e': 7}  # __iter__
True
>>> len(s)  # __len__
5
>>>
>>> d2['c'] = 11  ## update original dicts
>>> del d2['b']
>>> del d3['c']
>>> del d1['b']
>>>
>>> s['a']  # __getitem__, from d1['a']
1
>>> s['b']  # 'b' nor found in neither d1, d2 nor d3
KeyError: 'b'
>>> s['c']  # from d2['c']
11
>>> s['d']  # from d2['d']
5
>>> s['e']  # from d3['e']
7
>>> len(s)  # 'b' is no longer here
4

__init__(*mps: collections.abc.Mapping)

Constructor of StackedMapping.

Later mappings will be stacked on top of the earlier ones.

Parameters:

mps – Multiple mapping objects.