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Python List




Python – List


As we read earlier about Python Loop. Now we will study about List in Python. In python programming language, we will cover define a list, create a list , list operations, list constructor python, how to add two lists in python etc. So let’s start reading about the first collection of data type.





What is a List in python ?

List is a collection / sequence of Heterogeneous data type. List is a mutable data type i.e. they can be edited or modified.  In python list are written with Square Brackets.



List syntax python
:

List variable = [ comma separated element ]



Python list Example : How to make a list ?

list_1 = [5, "Black", 3.5, "White", 75, "Blue"]
print(list_1)



Output :

[5, 'Black', 3.5, 'White', 75, 'Blue']




How to access the list from a list ?

We can access the list items by using the index number.



Example :

          0     1      2      3     4     5 
          ↓     ↓      ↓      ↓     ↓     ↓ 
list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
print(list_1[3])



Output :

White




How to access the list items by using negative indexing ?

Negative indexing means beginning from the end i.e. – 1 refers to the last item, – 2 refers to the second last item, – 3 refers to the third last item.



List Example :

         -6     -5    -4     -3    -2    -1 
          ↓      ↓     ↓      ↓     ↓     ↓ 
list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
print(list_1[-3])



Output :

White




How to access the list items by using Range of Indexes ?

Range of Indexes means where to start the range and where to end the range.



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
print(list_1[1:5])



Output :

['Black', 3.5, 'White', 75]




You can leave the start value blank, so the range will start at the first item



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
print(list_1[:4])

The above example returns the items from the beginning to  “White”.



Output :

[5, 'Black', 3.5, 'White']




You can leave the end value blank, so the range will go to the end of the list



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
print(list_1[2:])

The above example return the items from ” 3.5 ” to end.



Output :

[3.5, 'White', 75, 'Blue']




How to access the list items by using Range of Negative Indexing ?

Negative indexing means beginning from the end i.e. – 1 refers to the last item , – 2 refers to the second last item, – 3 refers to the third last item. 



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
print(list_1[-4:-1])



Output :

[3.5, 'White', 75]




How to change the item value ?

To change the value of a specific item, by using the index number.



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
list_1[3]="Red" 
print(list_1)



Output :

[5, 'Black', 3.5, 'Red', 75, 'Blue']




Loop through a list

You can print all the list items by using the ” For” loop.



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
for i in list_1: 
    print(i)



Output :

5 
Black 
3.5 
White 
75 
Blue

loops in detail :  https://codifyshow.com/python-loop/





How to check the length of a given list ?

You can check the length of a given list, by using the len( ) function.



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
print(len(list_1))



Output :

6




Copy a list

You can make a copy of a list by using copy( ) function.



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
list_2 = list_1.copy() 
print(list_2)



Output :

[5, 'Black', 3.5, 'White', 75, 'Blue']




There is an alternative method to make a copy of a list by using the built-in method list( ).



Example :

list_1 = [5, "Black", 3.5, "White", 75, "Blue"] 
list_2 = list_1.copy() 
print(list_2)



Output :

[5, 'Black', 3.5, 'White', 75, 'Blue']




Joining two list

You can join or concatenate two or more lists in python.



Example :

list_1 = ["Black", "White", "Red"] 
list_2 = [5, 3.5, 75] 
list_3 = list_1 + list_2 
print(list_3)



Output :

['Black', 'White', 'Red', 5, 3.5, 75]



list( ) constructor

There is an alternative to make a new list by using the list( ) constructor.



Example :

list_1 = list(("Black", "White", "Blue")) 
print(list_1)



Output :

['Black', 'White', 'Blue']

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