How Does Tuple Swapping Work Internally in Python?

How does Swapping of Members in Tuples (a, b) = (b, a) Work Internally?

The swapping of members in tuples is performed through a series of stack operations without using a temporary variable. Python separates the right-hand side expression from the left-hand side assignment.

For tuples with 2 or 3 items:

The right-hand side is evaluated, pushing [a, b] onto the stack. The ROT_TWO opcode swaps the top two positions, resulting in [b, a] at the top. The STORE_FAST opcodes then store these values in the left-hand side variables without a temp variable.

For tuples with 4 or more items:

An explicit tuple is built from the right-hand side expressions. The UNPACK_SEQUENCE opcode pops the tuple off the stack and pushes its elements back onto the stack in reverse order. The subsequent STORE_FAST operations store these values in the left-hand side variables.

Optimization for 2 and 3-name Assignments:

Peephole optimization replaces the inefficient BUILD_TUPLE/UNPACK_SEQUENCE combination with faster ROT_TWO/ROT_THREE opcodes for 2 and 3-name assignments.

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