Explanation for output in Python

Question

I came across a piece of python code, requiring me to give the output. The code goes as follows:

a = [1, 2]
b = [a, 3]
c = b[:]
a[0] = 7
b[1] = 8
print c

I thought the output to be [[7, 2], 8] since i have the reference to the a in b, and consequently, c had the reference to b

But the output came out to be [[7, 2], 3]

What am I missing here?

Unlike c = b c = b[:] creates a (flat) copy of b as c. Changes in b are not reflected to c. — Klaus D.
– Klaus D., Commented Dec 11, 2018 at 14:31
have a look to this:programiz.com/python-programming/shallow-deep-copy — Kian
– Kian, Commented Dec 11, 2018 at 14:45
@KlausD. if changes in b are not reflected in c , how come the changes in a are getting reflected in c ? — Abhisek Chaudhuri
– Abhisek Chaudhuri, Commented Dec 11, 2018 at 14:54

jedwards · Accepted Answer · 2018-12-11 14:31:10Z

5

c had the reference to b

This is where you went wrong. c is initialized as a (shallow) copy of b.

If it were simply c = b (without the [:]) then you'd be correct.

answered Dec 11, 2018 at 14:31

jedwards

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1 Comment

Had to clear a lot of concepts about shallow copy and deep copy. Thanks for the response. Marking it as accepted!