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Python math.perm() Method

The Python math.perm() method is used to calculate the number of permutations of "k" items chosen from a set of "n" distinct items in a specific order. Mathematically, it is denoted as −

P(n,\:k)\:=\:\frac{n!}{(n\:-\:k)!}

Where, n! represents the factorial of "n", which is the product of all positive integers from 1 to n, and (nk)! represents the factorial of (n-k).

For example, if you have a set of "5" distinct items and you want to arrange "3" of them, "math.perm(5, 3)" will return the number of permutations, which is 5!/(5-3)! = 5!/2! = 5 × 4 × 3 × 2 × 1/2 × 1 =60.

Following is the basic syntax of the Python math.perm() method −

math.perm(n, k)

This method accepts the following parameters −

• x − It is the total number of items or elements.

• y − It is the number of items to be arranged (permutations).

The method returns the permutation of the given values "n" and "k".

In the following example, we are calculating the number of permutations of selecting "3" elements from a set of "5" distinct elements −

import math
result = math.perm(5, 3)
print("The result obtained is:",result)         

The output obtained is as follows −

The result obtained is: 60

Here, we are calculating the number of permutations of selecting "2" elements from a set of "4" elements with replacement allowed −

import math
result = math.perm(4, 2)
print("The result obtained is:",result)  

Following is the output of the above code −

The result obtained is: 12

Now, we are calculating the number of permutations of arranging the letters of the word "MISSISSIPPI" while considering the duplicate letters −

import math
word = "MISSISSIPPI"
n = len(word)
result = math.perm(n)
print("The result is:",result)  

We get the output as shown below −

The result is: 39916800

In this example, we are calculating the number of permutations of selecting "0" elements from an empty set −

import math
result = math.perm(0, 0)
print("The result obtained is:",result)  

The result produced is as shown below −

The result obtained is: 1

python_maths.htm

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