Append JSON element to a list

Question

x = []
a = {'sample': True}
x.append(a)
a["sample"] = False
x.append(a)
print(x)

The current result is [{'sample': False}, {'sample': False}].

I need the response to be [{'sample': True}, {'sample': False}].

I've tried x.update({"sample": False}); same effect.

You change a ["sample"] to false before you append it, so you will never get your desired output — JeffUK, Dec 02 '20 at 17:49
PS.. this is not a JSON Element, is a dictionary with a single entry. — JeffUK, Dec 02 '20 at 17:51
When you do `x.append(a)` you are appending a *reference* to the `dict`. So, when you change `a`. you are also changing the element in the list. — gen_Eric, Dec 02 '20 at 17:52
Why not just do x.append({'sample':False}) instead of using 'a' at all? Why do you need to copy the dictionary before you edit it at all? these seems to be adding unnecessary complication — JeffUK, Dec 02 '20 at 17:53

score 2 · Answer 1 · edited Dec 04 '20 at 05:26

2

You are appending the 'pointer' (python object) of dictionary, not a copy.

You can try:

def copyof(dico): return {**dico}
a = {'a':True}
x.append(copyof(a))

It will be Ok

edited Dec 04 '20 at 05:26

marc_s

answered Dec 02 '20 at 17:50

Henry

3

Note that this is a shallow copy. If there's any deeper nesting it'll require a deep copy. – John Kugelman Dec 02 '20 at 17:52
He didn't need deepcopy – Henry Dec 02 '20 at 17:52
We don't know since the OP says this is sample code. The real code might have a more complex object. It's worth mentioning. – John Kugelman Dec 02 '20 at 17:54
import copy x.append(copy.deepcopy(a)) – MR Sample Dec 02 '20 at 18:02

1 Answers1