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#python で値を持った既存の辞書に、デフォルト値つきの辞書をマージする例 ( もう if 'key' in dict なんて書きたくないんですよ‥ ) - Qiita

Using collections defaultdict and ChainMap together

wanna do

This dictionary d = {"a":1, "b",2}
When calling this way d["c"]
I want the default value to be entered instead of KeyError

example

 from collections import defaultdict 
 import collections 
 
 existing_dict = {"a":1, "b":2} 
 
 default_dict = defaultdict(int) 
 
 merged_dict = collections.ChainMap(existing_dict, default_dict)

EXE

 Python 3.7.2 (default, Jan 13 2019, 12:50:01) 
 [Clang 10.0.0 (clang-1000.11.45.5)] on darwin 
 Type "help", "copyright", "credits" or "license" for more information. 
 >>> from collections import defaultdict 
 >>> import collections 
 >>> existing_dict = {"a":1, "b":2} 
 >>> default_dict = defaultdict(int) 
 >>> merged_dict = collections.ChainMap(existing_dict, default_dict) 
 >>> merged_dict["a"] 
 1 
 >>> merged_dict["b"] 
 2 
 >>> merged_dict["c"] 
 0 
 >>> merged_dict["d"] 
 0

ps

Maybe we aren't doing something really careless
Please write from the white goat if something is wrong

Original by Github issue

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