# Python math.perm() – Permutations

Contents

## Python math.perm()

math.perm(n, k) function returns the number of ways to choose k items from n items without repetition and with order.

``perm(n, k) = n! / (n - k)!``

## Syntax

The syntax to call perm() function is

``math.perm(n, k=None)``

where

If k is not given, perm(n) returns n!.

If either n or k is not an integer, then perm() raises TypeError.

If either n or k is negative, then perm() raises ValueError.

## Examples

### 1. Permutations of picking 2 items out of 5

In the following program, we find the number of permutations of picking 2 items out of 5.

Python Program

``````import math

n = 5
k = 2
result = math.perm(n, k)
print('perm(n, k) :', result)``````
Run Code Copy

Output

``perm(n, k) : 20``

### 2. perm(n, k) when k is not given

If we do not pass any value for parameter k, then perm() returns all the possible permutations for given n.

Python Program

``````import math

n = 4
result = math.perm(n)
print('perm(n) :', result)``````
Run Code Copy

Output

``perm(n) : 24``

### 3. perm(n, k) when n is negative

If n is negative, then perm() throws ValueError.

Python Program

``````import math

n = -5
k = 2
result = math.perm(n, k)
print('perm(n, k) :', result)``````
Run Code Copy

Output

``ValueError: n must be a non-negative integer``

### 4. perm(n, k) when n is a float value

If n is a floating point number, then perm() throws TypeError.

Python Program

``````import math

n = 5.1
k = 2
result = math.perm(n, k)
print('perm(n, k) :', result)``````
Run Code Copy

Output

``TypeError: 'float' object cannot be interpreted as an integer``

## Summary

In this Python Math tutorial, we learned the syntax of, and examples for math.perm() function.

## Related Tutorials

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