python ChainMap的使用和说明详解

from collections import ChainMap
a = {"x":1, "z":3}
b = {"y":2, "z":4}
c = ChainMap(a,b)
print(c)
print("x: {}, y: {}, z: {}".format(c["x"], c["y"], c["z"]))

In [6]: a = {"x":1, "z":3}

In [7]: b = {"y":2, "z":4}

In [8]: c = ChainMap(a, b)

In [9]: c
Out[9]: ChainMap({'z': 3, 'x': 1}, {'z': 4, 'y': 2})

In [10]: c["z"]
Out[10]: 3

In [11]: c["z"] = 4

In [12]: c
Out[12]: ChainMap({'z': 4, 'x': 1}, {'z': 4, 'y': 2})

In [13]: c.pop('z')
Out[13]: 4

In [14]: c
Out[14]: ChainMap({'x': 1}, {'z': 4, 'y': 2})

In [15]: del c["y"]
---------------------------------------------------------------------------
KeyError                 Traceback (most recent call last)
。。。。。。
KeyError: "Key not found in the first mapping: 'y'"

In [4]: a = ChainMap()

In [5]: a["x"]=1

In [6]: a
Out[6]: ChainMap({'x': 1})

In [7]: b = a.new_child()

In [8]: b
Out[8]: ChainMap({}, {'x': 1})

In [9]: b["x"] = 2

In [10]: b
Out[10]: ChainMap({'x': 2}, {'x': 1})

In [11]: b["y"] = 3

In [12]: b
Out[12]: ChainMap({'x': 2, 'y': 3}, {'x': 1})

In [13]: a
Out[13]: ChainMap({'x': 1})

In [14]: c = a.new_child()

In [15]: c
Out[15]: ChainMap({}, {'x': 1})

In [16]: c["x"]
Out[16]: 1

In [17]: c["y"] = 1

In [18]: c
Out[18]: ChainMap({'y': 1}, {'x': 1})

In [19]: d = c.parents()
---------------------------------------------------------------------------
TypeError                 Traceback (most recent call last)
<ipython-input-19-dc4debb7ca3b> in <module>()
----> 1 d = c.parents()

TypeError: 'ChainMap' object is not callable

In [20]: d = c.parents

In [21]: d
Out[21]: ChainMap({'x': 1})

In [22]: d is a
Out[22]: False

In [23]: d == a
Out[23]: True

In [24]: a = {"x":1, "z":3}

In [25]: b = {"y":2, "z":4}

In [26]: c = ChainMap(a,b)

In [27]: c
Out[27]: ChainMap({'x': 1, 'z': 3}, {'y': 2, 'z': 4})

In [28]: c.maps
Out[28]: [{'x': 1, 'z': 3}, {'y': 2, 'z': 4}]

In [29]: c.parents
Out[29]: ChainMap({'y': 2, 'z': 4})

In [30]: c.parents.maps
Out[30]: [{'y': 2, 'z': 4}]

In [31]: c.parents.parents
Out[31]: ChainMap({})

In [32]: c.parents.parents.parents
Out[32]: ChainMap({})