make use of collections.ChainMap to simplify the code

[linchiwei123]

No description provided.

[felixxm]

Thanks for this patch, however ChainMap is more complicated structure that is not a "normal" dict:

>>> a = {'b': 1, 'c': 18, 'd': 90}
>>> b = {'c': 77}
>>> c = {'c': 88, 'd': 91, 'e': 115, 'f': 300}
>>> isinstance(ChainMap(a, b, c))
False
>>> ChainMap(a, b, c)
ChainMap({'b': 1, 'c': 18, 'd': 90}, {'c': 77}, {'c': 88, 'd': 91, 'e': 115, 'f': 300})

Moreover it has different order of keys, e.g.

>>> list(ChainMap(a, b, c).keys())
['b', 'c', 'd', 'e', 'f']
>>> list(merge_dicts([a, b, c]).keys())
['c', 'd', 'e', 'f', 'b']

[linchiwei123]

Thanks for this patch, however ChainMap is more complicated structure that is not a "normal" dict:

>>> a = {'b': 1, 'c': 18, 'd': 90}
>>> b = {'c': 77}
>>> c = {'c': 88, 'd': 91, 'e': 115, 'f': 300}
>>> isinstance(ChainMap(a, b, c))
False
>>> ChainMap(a, b, c)
ChainMap({'b': 1, 'c': 18, 'd': 90}, {'c': 77}, {'c': 88, 'd': 91, 'e': 115, 'f': 300})

Moreover it has different order of keys, e.g.

>>> list(ChainMap(a, b, c).keys())
['b', 'c', 'd', 'e', 'f']
>>> list(merge_dicts([a, b, c]).keys())
['c', 'd', 'e', 'f', 'b']

Thanks for the information.