# Flatten list Python

Flatten list in python means converting a multidimensional list into a single dimension list. the user can also perform the same for nested lists as well. For example, if the user wishes to convert [2,3,4], [12,32] into flatten list, the output will be [2,3,4,12,32]. This process of converting a multi-dimension list into a flatten list is called flattening. This method is performed by either using loops inside loops to flatten.

To Understand about Python Data Types

Flattening can be done in a number of ways such as by nested loops, by using some library functions in the code, by += operator, reduce method, NumpyFlat etc. The best way user can consider for flattening is nested loops though.

## Flatten Program nested loops in python

``````List = [[10,25,36],[41,50,68],[70,87,94]]
List_flat = []

for i in range(len(List)):
for j in range (len(List[i])):
List_flat.append(List[i][j])

print("Original List:",List)
print("Flattened List:",List_flat)
``````

The output of the above python program will be:

``````Original List: [[10, 25, 36], [41, 50, 68], [70, 87, 94]]
Flattened List: [10, 25, 36, 41, 50, 68, 70, 87, 94]``````

The task in the above program is that the whole loss of the nested list is now a single form of flattening list. There can be unlimited lists to flatten. This can also be done using another method with is by importing itertools.

## Flatten list python itertools

``````import itertools
lists = [[10,25,36],[41,50,68],[70,87,94]]
joinedlist = list(itertools.chain(*lists))
print(joinedlist)``````

The output of the above python program will be:

``[10, 25, 36, 41, 50, 68, 70, 87, 94]``

#### Check out the program below for flattening the lists using += operator in python:

``````
lists = [[10,25,36],[41,50,68],[70,87,94]]
joinedlist = []
for list in lists:
joinedlist += list

print(joinedlist)``````

The output of the above code using += operator will be:

``````[10, 25, 36, 41, 50, 68, 70, 87, 94]
``````

#### There are some pre-defined rules for flattening the list which are:

• The nested lists have to be present inside the square brackets only.
• The flattened list will be return inside the square brackets only.
• Flatten list will only remove the inner brackets of the  enclosed elements.
• It is not possible to perform any calculations inside the square brackets or inner lists.