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# How to generate all Permutations of a List

In this article, we will learn how to generate all possible permutations of a list in Python. We will use some built-in functions and some custom codes as well. Let's first have a quick look over what is a list and what is permutation in Python.

## Python List

Python has a built-in data type called list. It is like a collection of arrays with different methodology. Data inside the list can be of any type say, integer, string or a float value, or even a list type. The list uses comma-separated values within square brackets to store data. Lists can be defined using any variable name and then assigning different values to the list in a square bracket. The list is ordered, changeable, and allows duplicate values. For example,

``````list1 = ["Ram", "Arun", "Kiran"]
list2 = [16, 78, 32, 67]
list3 = ["apple", "mango", 16, "cherry", 3.4]``````

We all have heard and studied the permutation concept in mathematics, likewise, Python supports some built-in functions to generate permutations of a list. Python provides a standard library tool to generate permutations by importing `itertools` package to implement the `permutations` method in python. We will also discuss the recursive method to generate all possible permutations of a list.

### Example Generate Permutations of a list

The below example passes the given list as an argument to `itertools.permutations()` function. It defaults to the length of the list and hence generates all possible permutations.

``````import itertools

list1 = [1, 2, 3]

perm = list(itertools.permutations(list1))

print(perm)``````

[(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]

### Example: Generate successive 'r' length permutations of a list

The below example passes the given list and length as an argument to `itertools.permutations()` function. It generates the permutations of the given length.

``````import itertools
list1 = [1, 2, 3]
r = 2
perm = list(itertools.permutations(list1, r))
print(perm)``````

[(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2)]

## Example: Generate Permutations of a list

The below example takes an empty list to store all permutations of all possible length of a given list. `extend()` function is used to add items to the empty list one after the other. Iterating over the elements of the list using for loop, the `itertools.permutations()` function finds all the possible lengths.

``````import itertools

list1 = [1, 2, 3]

perm = []

for i in range(1,len(list1)+1):
perm.extend(list(itertools.permutations(list1, r=i)))
print(perm)
``````

[(1,), (2,), (3,), (1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2), (1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]

## Example: Recursion method to generate all permutations of a list

The below example uses recursion to generate all permutations of a list. It defaults to the length of the list and hence generates all possible permutations.

``````def perm(start, end=[]):
if(len(start) == 0):
print(end)
else:
for i in range(len(start)):
perm(start[:i] + start[i+1:], end + start[i:i+1])

#function call
perm([1,2,3])
``````

[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 1, 2]
[3, 2, 1]

### Conclusion

In this article, we learned to generate all possible permutations of a list by using `itertools.permutations()` function and `recursive` method. We discussed them with different examples.