How to slice a list in python ?

August 07, 2021    /    Viewed: 242    /    Comments: 0    /    Edit


Examples of how to slice a list in python:

Create a list in python

Lets first create a list in python

mylist = ['a','b','c','d','e','f','g','h','i']

To get an element stored in a list using its indexe:

mylist[0]

returns

'a'

and

mylist[4]

returns

'e'

Get number of elements in a list

To get the size of a list in python, a solution is to use the built-in function len()

s = len(mylist)

print(s)

returns here

9

Get first n elements of a list in python

To get first n elements of a list in python a solution is to do mylist[-n:]. Example, extract only the first 3 elements:

mylist[:3]

returns

['a', 'b', 'c']

same as

mylist[0:3]

also returns

['a', 'b', 'c']

Get last n elements of a list in python

To get last n elements of a list in python a solution is to do mylist[-n:]. Example, extract only the last 2 elements:

mylist[-2:]

returns

['h', 'i']

Note: same as doing:

mylist[s-2:s]

also returns

['h', 'i']

Get elements between indexes m,n

To get elements between indexes m,n, a solution is to do mylist[m:n]. Example:

mylist[2:5]

returns

['c', 'd', 'e']

Get every nth element in a list

To get for example every 2 element in a list

mylist[::2]

returns

['a', 'c', 'e', 'g', 'i']

Another example

mylist[::3]

returns

['a', 'd', 'g']

Get every nth element in a list, between indexes m1,m2

To get every nth element in list, between indexes m1,m2, a solution is to do mylist[m1:m2:n]. Example:

mylist[0:4:2]

returns

['a', 'c']

References


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