Swapping two variables without using a third (temporary) variable (Python)

2015-09-19T19:51:22-07:00

Python recipe 579101 by Vasudev Ram (swap).

This recipe shows how to swap the values of two variables without making use of a third, temporary variable. The traditional method of swapping two variables is using a temp variable.

The first method shown here, swaps two variables an and b without using a temp variable. The variables a and b are integers:

a = 1, b = 2

Prints original values of a and b, i.e. 1 and 2:

print a, b a = a + b b = a - b a = a - b

Prints swapped values of a and b, i.e. 2 and 1:

print a, b

The above swap method, using arithmetic expressions, will not work for non-numeric data types, and may also not work (at least in some cases) for floats. But the method below should work for any type of Python variable:

It even works for function objects. If you have:

def foo(): print "This is foo()." def bar(): print "This is bar()."

and then:

foo(), bar()

and then:

foo, bar = bar, foo

then see what happens to values foo and bar, when you do:

foo() bar()

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Swapping two variables without using a third (temporary) variable (Python)

Prints original values of a and b, i.e. 1 and 2:

Prints swapped values of a and b, i.e. 2 and 1: