A simple swap program

crystalattice · #1 16-Oct-2005, 01:02

When you want to swap numbers in C/C++, you might write something like this:

CPP / C++ / C Code:

include <stdio.h>

void swap(int *i, int *j)
{
    int t;
    t = *i;
    *i = *j;
    *j = t;
}

void main()
{
    int a,b;
    a=5;
    b=10;
    printf("%d %d\n",a,b);
    swap(&a,&b);
    printf("%d %d\n",a,b);
}

In Python, there's an extremely easy way to swap to items; you just tell Python to do it for you:

Python Code:

>>>nudge = 1
>>>wink = ["spam", "eggs"]
>>>nudge, wink = wink, nudge   #tuples: swaps values
                               #same as T=nudge; nudge=wink; wink=T
>>>print nudge, wink

When tuples appear on both sides of an assignment operator (=), Python assigns objects on the right to targets on the left, according to their positions. This is probably easiest to understand by realizing the objects on the left don't make a tuple, they just look like it. They are simply a set of independent assignment targets. The items on the right are a tuple, which get unpacked during the assignment (the tuple provides the temporary assignment needed to achieve the swap effect).

Naturally you can use this method to swap any object types, like integers, floats, lists, etc. and you can have as many values swapped as necessary.

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