The exchange operation, sometimes called a swap, is slightly different in Python than in most other programming languages. Typically, swapping two elements in a list requires a temporary variable (an additional memory location). A code fragment such as
temp = a_list[i] a_list[i] = a_list[j] a_list[j] = temp
will exchange the -th and -th items in the list. Without the temporary storage, one of the values would be overwritten.
In Python, it is possible to perform simultaneous assignment. The statement
a, b = b, a will result in two assignment statements being done at the same time. Using simultaneous assignment, the exchange operation can be done in one statement.