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In this post, we will learn about lists in Python ,how they are created, adding and removing  items ,copy list,join lists and so on.

Python lists


What's the list?

  • The list is a type of container.
  • The list is a data structure in Python that is a changeable and ordered sequence of elements.
  • Lists allow duplicate members.
  • In Python, lists are written with square brackets.

How to create lists in Python?

  • The syntax is listName=[ ] .
  • list is defined by having values between square brackets [ ] and the values are separated by a comma.
  • list can have any numbers of items and these items may be in different types.
  • List can contain other lists as items.

Ex:

#list with string elements
colorList=["Red", "Green", "White", "Black", "blue"]

#list with different data types
mylist=["red",1,1.2]

#list with nested lists
nestedList=[[1,2,3], "Red",[4,5]]

How to access list in Python?

  • You can access the list item using the index operator.
  • Nested lists can be accessed by using a nested index.
  • Negative index means beginning from the end -1 index refers to the last item in the list, -2 the second item from the end, and so on.
  • You can specify a range of indexes "start and the end" where the return value is a sub list from the original list, and this range can be positive or negative ranges.

Ex:

colorList=["Red", "Green", "White", "Black", "Blue"]
print(colorList[0]) # it return the first item Red
print(colorList[-1]) # it return the last item Blue

print(colorList[2:4]) 
# it return sub list from 2 (included) to 4 (excluded) ['White','Black']

print(colorList[-3:-1]) 
# it return sub list from -3 (included) to -1 (excluded) ['Blue','Black']

print(colorList[2:]) 
# it return sub list from 2 (included) to the end ['White','Black', 'Blue'] 

print(colorList[:2]) 
# it return sub list from the beginning to index 2 (excluded) ['Red','Green']

print(colorList[-2:]) 
# it return sub list from -2 (included) to the end ['Black', 'Blue'] 

print(colorList[:-2])
 # it return sub list from the beginning to index -2 (excluded) ['Red','Green','White']

How to change list item value?

Change the list item value by using the item index.

Ex:

colorList=["Red", "Green", "White", "Black", "Blue"]
colorList[0]="yellow"
print(colorList)
# the output will be ['yellow', 'Green', 'White', 'Black', 'Blue']

Check if Exists

  • check if a given item exists in the current list or not. 
  • It is performed by using in a keyword.
colorList=["Red", "Green", "White", "Black", "Blue"]
if "Red" in colorList:
   print("Red is found")

Python list methods

append()

It adds item to the end of the list.

Ex:

colorList=["Red", "Green", "White", "Black", "Blue"]
colorList.append("orange")
print(colorList)
# the output will be ['Red','Green', 'White', 'Black','Blue','orange']

insert()

It add an item to a specific index.

Ex:

colorList=["Red", "Green", "White", "Black", "Blue"]
colorList.insert(1,"orange")
print(colorList)
# the output will be ['Red','orange','Green', 'White', 'Black','Blue']

remove()

It remove a specific item.

Ex:

colorList=["Red", "Green", "White", "Black", "Blue"]
colorList.remove("Red")
print(colorList)
# the output will be ['Green', 'White', 'Black','Blue']

extend()

It adds the content of one list to the end of the other list.

Ex: 

in this example, we will add the content of the list which name is  colorList2 to the end of colorList1

colorList1=["White", "Black", "Blue"]
colorList2=["Red", "Green"]
colorList1.extend("colorList2") print(colorList1) 
# the output will be ['White', 'Black','Blue','Red','Green']

pop()

It removes items from a specific index. or the last index, if you do not specify an index.

Ex:

colorList=["Red", "Green", "White", "Black", "Blue"]
colorList.pop(1)
print(colorList)# the output will be ['Red', 'White', 'Black','Blue']

del keyword

  • It removes item from a specific index.
  • or it removes the list itself.

Ex:

colorList=["Red", "Green", "White", "Black", "Blue"]
del colorList[0]
print(colorList)# the output will be ['Green', 'White', 'Black','Blue']
del colorList # the list is no longer exist

copy()

It copies alist in another list

Ex:

colorList=["Red", "Green", "White", "Black", "Blue"]
copycolorList=colorList.copy()
print(copycolorList)#the output will be ['Red', 'Green', 'White', 'Black','Blue']

sum()

calculates the sum of all elements in the list.

sum used only for numeric values other wise it will raise a type error

Ex:

List=[1,2,3,4]
print(sum(List))
#the output will be 10

count()

used to calculate the numbers of occurrence for a specific element in the list.

Ex:

List=[1,2,1,3,4]
print(count(1))
#the output will be 2

len()

used to calculate the total number of elements in the list.

Ex:

List=[1,2,1,3,4]
print(len(List))
#the output will be 5

index()

used to return the first appearance of a specific element in the list.

Ex:

List=[1,2,1,2,3,4]
print(List.index(2))
#the output will be 1

min()

used to return the minimum of all elements in the list.

Ex:

List=[5,2,1,3,4]
print(min(List))
#the output will be 1

max()

used to return the maximum of all elements in the list.

Ex:

List=[5,2,1,3,4]
print(max(List))
#the output will be 5

Conclusion 

In this post, we have explored python lists and how we can use it 

See Also


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