How swapping variables is implemented in Python?

Question

How does the below code work in Python:

a = input()
b = input()
a, b = b, a  # STATEMENT 1
print(a, b)

Does the statement 1 create a third variable in Python heap memory space to swap the two numbers or does it use some algorithm to do the swap?

Answer 1

It's a simple bytecode operation which doesn't need any intermediate variables to do the swap. See this demo:

import dis

code = '''
a = input()
b = input()
a, b = b, a
'''

dis.dis(code)

Output:

 2           0 LOAD_NAME                0 (input)
             2 CALL_FUNCTION            0
             4 STORE_NAME               1 (a)

 3           6 LOAD_NAME                0 (input)
             8 CALL_FUNCTION            0
            10 STORE_NAME               2 (b)

 4          12 LOAD_NAME                2 (b)
            14 LOAD_NAME                1 (a)
            16 ROT_TWO
            18 STORE_NAME               1 (a)
            20 STORE_NAME               2 (b)
            22 LOAD_CONST               0 (None)
            24 RETURN_VALUE

Note: Like bytecode as a whole, this is of course just an implementation detail of CPython.