Python – math.perm() 方法

Python中的数学模块包含许多数学运算，可以使用该模块轻松执行。 Python中的math.perm()方法用于获取从 n 个项目中选择 k 个项目的方法数，不重复且有顺序。它评估为n! /（n - k）！当k <= n时，当k > n时计算为 0。
此方法是Python 3.8 版中的新方法。

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!.

代码 #1：使用math.perm()方法

# 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)

输出：

90
60

代码 #2：当 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)

输出：

0

代码 #3：如果未指定 k

# 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)

输出：

120

参考： Python数学库