Python – math.perm() method

Math module in Python contains a number of mathematical operations, which can be performed with ease using the module. math.perm() method in Python is used to get the number of ways to choose k items from n items without repetition and with order. It Evaluates to n! / (n – k)! when k <= n and evaluates to 0 when k > n.
This method is new in Python version 3.8.

Syntax: math.perm(n, k = None)

Parameters:
n: A non-negative integer
k: A non-negative integer. If k is not specified, it defaults to None

Returns: an integer value which represents the number of ways to choose k items from n items without repetition and with order. If k is none, method returns n!.

Code #1: Use of math.perm() method

# Python Program to explain math.perm() method

# Importing math module
import math

n = 10
k = 2

# Get the number of ways to choose
# k items from n items without
# repetition and with order
nPk = math.perm(n, k)
print(nPk)

n = 5
k = 3

# Get the number of ways to choose
# k items from n items without
# repetition and with order
nPk = math.perm(n, k)
print(nPk)

Output:

90
60

Code #2: When k > n

# Python Program to explain math.perm() method

# Importing math module
import math

# When k > n
# math.perm(n, k) returns 0.
n = 3
k = 5

# Get the number of ways to choose
# k items from n items without
# repetition and with order
nPk = math.perm(n, k)
print(nPk)

Output:

0

Code #3: If k is not specified

# Python Program to explain math.perm() method

# Importing math module
import math

# When k is not specified
# It defaults to n and
# math.perm(n, k) returns n ! n = 5

nPk = math.perm(n)
print(nPk)

Output:

120

Reference: Python math library