I have a list of dictionary let's say : l=[{'a':1,'b':2},{'a':5,'b':6},{'a':3,'b':2}] and I want to have another list l2 and add 4 to the 'a' in the all dictionaries
l2=[{'a':5,'b':2},{'a':9,'b':6},{'a':7,'b':2}] (the first list l shouldn't change) so I am doing it this way but i feel there is better, it is a bit hard coded I think :

l2=[d.copy() for d in l]
for v in l2:
  • 2
    \$\begingroup\$ Can you show more of your code? Currently this seems somewhat hypothetical. \$\endgroup\$
    – Reinderien
    Commented Nov 6, 2020 at 14:38

1 Answer 1


Should have spaces around =, and += would shorten it a bit. And I'd be consistent with the variable name (not switch from d to v) and use better names for the lists (l looks too much like 1 and is just too short for something presumably living longer (unlike d, which I find ok in such small contexts)):

lst2 = [d.copy() for d in lst]
for d in lst2:
    d['a'] += 4

I'd say that's alright then. But here are two alternatives:

>>> [d | {'a': d['a'] + 4} for d in lst]
[{'a': 5, 'b': 2}, {'a': 9, 'b': 6}, {'a': 7, 'b': 2}]
>>> [{**d, 'a': d['a'] + 4} for d in lst]
[{'a': 5, 'b': 2}, {'a': 9, 'b': 6}, {'a': 7, 'b': 2}]
  • \$\begingroup\$ thank you , this is what I was looking for ,i was feeling it can be done in one line of code, and yes for the variables I know it was just a quick example of what I wanted to do in my real code I am using more significant variable names \$\endgroup\$ Commented Nov 9, 2020 at 16:27

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