# Get the number of permutations in Python: Calculate nPk (the number of ways to choose and order items)

The `perm()`

in `math`

module returns the number of patterns to choose k objects from n objects and order them, that is _{n}P_{k}.

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

The method is available from Python 3.8. The first argument is the number of total items and the second is the number of items you choose and order.

## Example

Here is the examples of choosing 0 to 5 items from 5 items and ordering.

```
import math
p0 = math.perm(5, 0)
p1 = math.perm(5, 1)
p2 = math.perm(5, 2)
p3 = math.perm(5, 3)
p4 = math.perm(5, 4)
p5 = math.perm(5, 5)
print(p0, p1, p2, p3, p4, p5)
# 1 5 20 60 120 120
```

Choosing 2 items from 5 items with order has 20 ways.

perm(5, 2) = _{5}P_{2} = 5 × 4 = 20

## In case k is not specified

```
p = math.perm(5)
print(p) # 120
```

The `math.perm(5)`

and `math.perm(5, 5)`

are equivalent and both are equal to 5! = 120.

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