Key is the dictionary {:} stored value, defined by the braces {}, when used as a general-purpose "in the brackets [] + key" used; key only immutable data types: plastic, string, Yuan group.
-------------------------------------------------- variable with the data type immutable ----------------------------------------
Variable types: lists, dictionaries.
Immutable data types: plastic, string, a tuple.
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Is defined: dir = { 'name': 'fangxs', 'age': 18, 'sex': 'man'}
Call: print (dir [ 'name'])
Key can be integer, or tuple:
dir = {1:'fangxs',2:'age',('name','age'):(1,2)}
print (dir [1]) # output fangxs
print (dir [( 'name', 'age')]) # output (1,2)