Changing variable in instance not working when appending to list - Python

Question

Why is this not working as expected (at least for me)? I can't figure why.

class Fred:
    def __init__(self):
          self.a=0

fred=Fred()
lista=[]

for i in range(5):
    fred.a=i
    lista.append(fred)

for i in lista:
    print(str(i.a))

All I get is 5 times the number 4 and not from 0 to 4. Any comments? Thanks

this is bcoz all the elements in lista are referencing to the same element,, and the you see the number 4 since its the latest updated value of the object fred — avasal
– avasal, Commented Oct 28, 2012 at 4:46

Jay Taggart · Accepted Answer · 2012-10-28 04:46:14Z

1

What is happening is that the reference to Fred is being overwritten each time you loop in the for i in range(5). If you move the fred=Fred() inside that loop and create a new object each time, then you should see the expected result.

answered Oct 28, 2012 at 4:46

Jay Taggart

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Comments

icktoofay · Accepted Answer · 2012-10-28 04:46:53Z

0

You've got one Fred instance and keep adding that one instance to the list, changing its a property while you do that. Adding to the list does not copy the Fred object; it just adds another reference to the same object. You can get your expected behavior by creating a new Fred inside each iteration of the loop.

answered Oct 28, 2012 at 4:46

icktoofay

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