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Permutations and Combinations of a set of elements are different arrangements of the elements of the set.

**Combination**is a collection of the elements where the order doesn’t matter**Permutation**is an arrangement of a set where the order does matter.

Let’s consider a set as :

```
{A, B, C}
```

The permutations of the above set are as follows :

```
('A', 'B', 'C')
('A', 'C', 'B')
('B', 'A', 'C')
('B', 'C', 'A')
('C', 'A', 'B')
('C', 'B', 'A')
```

The combinations of the above set when two elements are taken together are :

```
('A', 'B')
('A', 'C')
('B', 'C')
```

In this tutorial, we will learn how to get the permutations and combinations of a group of elements in Python. We will look at sets of characters and numbers.

We will be using the **combinations()** and **permutations()** methods under the **itertools** module of Python.

Let’s get started.

To use the **permutations() method** under itertools module we will first need to import the module.

```
import itertools
```

Now let’s define a set of numbers.

```
val = [1, 2, 3, 4]
```

Now too get the list of permutations let’s use the permutations() method.

```
perm_set = itertools.permutations(val)
```

The line of code above gives an itertools object. To print the different permutations we will iterate over this object.

```
for i in perm_set:
print(i)
```

We get the output as :

```
1 2 3 4
1 2 4 3
1 3 2 4
1 3 4 2
1 4 2 3
1 4 3 2
2 1 3 4
2 1 4 3
2 3 1 4
2 3 4 1
2 4 1 3
2 4 3 1
3 1 2 4
3 1 4 2
3 2 1 4
3 2 4 1
3 4 1 2
3 4 2 1
4 1 2 3
4 1 3 2
4 2 1 3
4 2 3 1
4 3 1 2
4 3 2 1
```

The complete code for this section is given below :

```
import itertools
val = [1, 2, 3, 4]
perm_set = itertools.permutations(val)
for i in perm_set:
print(i)
```

Next we will learn how to get the permutations of characters in a string.

We will be using the permutations() method, but this time we will pass a string as an argument.

```
import itertools
s = "ABC"
perm_set = itertools.permutations(s)
for val in perm_set:
print(val)
```

Output :

```
('A', 'B', 'C')
('A', 'C', 'B')
('B', 'A', 'C')
('B', 'C', 'A')
('C', 'A', 'B')
('C', 'B', 'A')
```

We can find permutations of a set where we only take a specified number of elements in each permutation. This is similar to **nPr** in the field of mathematics.

The code for finding permutations of fixed length is given below:

```
import itertools
val = [1, 2, 3, 4]
perm_set = itertools.permutations(val,2)
for i in perm_set:
print(i)
```

Output :

```
(1, 2)
(1, 3)
(1, 4)
(2, 1)
(2, 3)
(2, 4)
(3, 1)
(3, 2)
(3, 4)
(4, 1)
(4, 2)
(4, 3)
```

Just like the method permutations(), we can use combinations(), also under itertools to get the combinations of a set.

While calling combinations() we need to pass two arguments, the set for finding combinations of and a number that signifies the length of each combination.

```
import itertools
val = [1, 2, 3, 4]
com_set = itertools.combinations(val, 2)
for i in com_set:
print(i)
```

Output :

```
(1, 2)
(1, 3)
(1, 4)
(2, 3)
(2, 4)
(3, 4)
```

We can also get combinations of a string. To get the combinations of a string, use the following piece of code :

```
import itertools
s = "ABC"
com_set = itertools.combinations(s, 2)
for i in com_set:
print(i)
```

Output :

```
('A', 'B')
('A', 'C')
('B', 'C')
```

There is another method under the itertools module called combinations_with_replacement(). This method takes under consideration the combination of a number with itself as well.

Let’s see how it works.

```
import itertools
val = [1, 2, 3, 4]
com_set = itertools.combinations_with_replacement(val, 2)
for i in com_set:
print(i)
```

Output :

```
(1, 1)
(1, 2)
(1, 3)
(1, 4)
(2, 2)
(2, 3)
(2, 4)
(3, 3)
(3, 4)
(4, 4)
```

You can see the difference in the output above and the output for the operation of a normal combination. Here we have combinations like (1,1) and (2,2) which are not there in regular combinations operation.

```
import itertools
val = "ABCD"
com_set = itertools.combinations_with_replacement(val, 2)
for i in com_set:
print(i)
```

Output :

```
('A', 'A')
('A', 'B')
('A', 'C')
('A', 'D')
('B', 'B')
('B', 'C')
('B', 'D')
('C', 'C')
('C', 'D')
('D', 'D')
```

This tutorial was about finding permutations and combinations of a set in python. We used itertools module available in python to find the permutations and combinations.

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