# 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

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