Python3 List of Dictionary

Question

I meet a strange phenomenon while dealing with list of dictionary in python3

oldlist = [{'name':'cheng'}]
ages = '18,20'
newlist = []

for ele in oldlist:
    for age in ages.split(','):
       ele['age'] = age
       newlist.append(ele)

print(newlist)

The result is :
[{'name': 'cheng', 'age': '20'}, {'name': 'cheng', 'age': '20'}]

What I am expected is 
[{'name': 'cheng', 'age': '18'}, {'name': 'cheng', 'age': '20'}]

Answer 1

That's because ele is still referencing the same dictionary in the next iteration. You'll need to create a copy. One way is to cast it to a dict:

for ele in oldlist:
    for age in ages.split(','):
        ele['age'] = age
        newlist.append(dict(ele))

or better yet, don't use oldlist, simply use ele itself for initialization:

ele = {'name':'cheng'}

for age in ages.split(','):
    ele['age'] = age
    newlist.append(ele)

Output:

[{'name': 'cheng', 'age': '18'}, {'name': 'cheng', 'age': '20'}]