Are python variables pointers? or else what are they?

python pointers variables identifier
Lior picture Lior · Nov 23, 2012 · Viewed 67.1k times · Source

Variables in Python are just pointers, as far as I know.

Based on this rule, I can assume that the result for this code snippet:

i = 5
j = i
j = 3 
print(i)

would be 3. But I got an unexpected result for me, it was 5.

Moreover, my Python book does cover this example:

i = [1,2,3]
j = i
i[0] = 5
print(j)

the result would be [5,2,3].

What am I understanding wrong?

Answer

John La Rooy picture John La Rooy · Nov 23, 2012

We call them references. They work like this

i = 5     # create int(5) instance, bind it to i
j = i     # bind j to the same int as i
j = 3     # create int(3) instance, bind it to j
print i   # i still bound to the int(5), j bound to the int(3)

Small ints are interned, but that isn't important to this explanation

i = [1,2,3]   # create the list instance, and bind it to i
j = i         # bind j to the same list as i
i[0] = 5      # change the first item of i
print j       # j is still bound to the same list as i

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