Deep copy of sublists

Question

I have a deep list a=[[1, 2], 3] for which I want to copy the first entry (the sublist) of the list multiple times to get [[1, 2], [1, 2], [1, 2], 3].

The following works:

a=[[1, 2], 3, 4]
for _ in range(2):
    a = [a[0][:]] + a
print(a) # [[1, 2], [1, 2], [1, 2], 3, 4]
a[0][0] = 5
print(a) # [[5, 2], [1, 2], [1, 2], 3, 4]

When doing a list comprehension, I create only shallow copies:

a=[[1, 2], 3, 4]
a = [a[0][:]] * (3) + a[1:]
print(a)    # [[1, 2], [1, 2], [1, 2], 3, 4]
a[0][0] = 5
print(a) # [[5, 2], [5, 2], [5, 2], 3, 4]

Question: How can I create deep copies of the sublist in a pythonic way?

`copy.deepcopy(a)` – Devesh Kumar Singh Jul 26 '19 at 16:01 — Devesh Kumar Singh, Jul 26 '19 at 16:01
What do you consider as *"pythonic"* way? – Austin Jul 26 '19 at 16:02 — Austin, Jul 26 '19 at 16:02
By pythonic I mean not using a loop :-) – Carsten Jul 26 '19 at 16:03 — Carsten, Jul 26 '19 at 16:03

score 1 · Accepted Answer · answered Jul 26 '19 at 16:01

1

You can't use *; use another list comprehension.

a = [a[0][:] for _ in range(3)] + a[1:]

answered Jul 26 '19 at 16:01

chepner

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Deep copy of sublists

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