# Python – Itertools Combinations() function

Itertool is a module of Python which is used to creation of iterators which helps us in efficient looping in terms of space as well as time. This module helps us to solve complex problems easily with the help of different sub-functions of itertools. The different sub-functions are divided into 3 subgroups which are:-

## Itertools.combinations()

`Itertools.combinations()` falls under the third subcategory called “Combinatoric Generators”. Combinatoric Generators are those iterators that are used to simplify combinatorial constructs such as permutations, combinations, and Cartesian products

As understood by name combinations is refers to a sequence or set of numbers or letters used in the iterator. Similarly `itertools.combinations()` provides us with all the possible tuples a sequence or set of numbers or letters used in the iterator and the elements are assumed to be unique on the basis of there positions which are distinct for all elements. All these combinations are emitted in lexicographical order. This function takes ‘r’ as input here ‘r’ represents the size of different combinations that are possible. All the combinations emitted are of length ‘r’ and ‘r’ is a necessary argument here.

Syntax:

`combinations(iterator, r)`

Example 1:-

 `# Combinations Of string "GeEKS" OF SIZE 3. ` ` `  ` `  `from` `itertools ``import` `combinations ` ` `  `letters ``=``"GeEKS"` ` `  `# size of combination is set to 3 ` `a ``=` `combinations(letters, ``3``)  ` `y ``=` `[``' '``.join(i) ``for` `i ``in` `a] ` ` `  `print``(y) `

Output:-

```['G e E', 'G e K', 'G e S', 'G E K', 'G E S', 'G K S', 'e E K', 'e E S', 'e K S', 'E K S']
```

Example 2:-

 `from` `itertools ``import` `combinations ` ` `  `     `  `print` `(``"All the combination of list in sorted order(without replacement) is:"``)    ` `print``(``list``(combinations([``'A'``, ``2``], ``2``)))   ` `print``()   ` `     `  `print` `(``"All the combination of string in sorted order(without replacement) is:"``)   ` `print``(``list``(combinations(``'AB'``, ``2``)))   ` `print``()   ` `     `  `print` `(``"All the combination of list in sorted order(without replacement) is:"``)   ` `print``(``list``(combinations(``range``(``2``), ``1``)))  `

Output :-

```All the combination of list in sorted order(without replacement) is:
[('A', 2)]

All the combination of string in sorted order(without replacement) is:
[('A', 'B')]

All the combination of list in sorted order(without replacement) is:
[(0,), (1,)]
```

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