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+--- Thread: Dict overwrite previous list (/thread-16917.html)
Dict overwrite previous list - vincentspm - Mar-20-2019
Temp = {}
Final = {}
OK =['OK','OK']
NOTOK =['NOTOK','NOTOK']
Temp[1] = OK
Final['u1']=Temp
print(Final)
Temp.clear()
Temp[2] = OK
Final['u2']=Temp
print(Final)
Temp.clear()
Temp[3] = NOTOK
Final['u3']=Temp
print(Final)would like to know why last print out overwrite previous one, need help.Actual result
{'u1': {1: ['OK', 'OK']}}
{'u1': {2: ['OK', 'OK']}, 'u2': {2: ['OK', 'OK']}}
{'u1': {3: ['NOTOK', 'NOTOK']}, 'u2': {3: ['NOTOK', 'NOTOK']}, 'u3': {3: ['NOTOK', 'NOTOK']}}
Expected result
{'u1': {1: ['OK', 'OK']}}
{'u1': {2: ['OK', 'OK']}, 'u2': {2: ['OK', 'OK']}}
{'u1': {3: ['OK', 'OK']}, 'u2': {3: ['OK', 'OK']}, 'u3': {3: ['NOTOK', 'NOTOK']}}
RE: Dict overwrite previous list - scidam - Mar-20-2019
This is well known feature of Python. Read about mutable and immutable objects in Python. Python dictionaries (and lists) are mutable objects, you can check this out by applying
id, e.g.somewhere after line #14 execute
id(Final['u1']) and id(Final['u2']). You will see that these id's are equal each other, that means the same objects are stored under keys
u1 and u2. So, when you change the underlying object, Temp (it is the same for all keys u1, u2, u3), everything 'changes immediately'.