Python List - index, slicing, append, del

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• The list represents the collection data of different types.
• The data stored in the list are separated by comma.
• The whole list is enclosed by square bracket([]).
• Use the slice[:] operator to access data from the list.
• The * symbol is used for the repetition operator and, the + symbol is used as a concatenation operator.

Syntax for Python List

• We can declare the list by using the following syntax.

List_name = [initial values]

For example

Age =[ 24,45,67,23,30]

• We can also declare the list with no initial value.

List_name = [ ]

• This kind of list is known as an empty list. We want to add the items to the list by using the append() function or method.

Accessing items from the list

There are two ways to access the items from the list.

• By using the index value
• By using slice notation

By Using the Index Value

• We can access the individual value by using the index value.
• The index has a range from zero to size-1.
• The first item is stored on the index value 0, the second item is on index value 1, and so on.

For example:
Age [0]=24,Age[1]=45

• We can also access the item on the list from the back.
• The last item has an index value of -1 and, the next item has an index value of -2 and so on.
• For instant, consider the above list.

  Age [-1]=30,Age[-2]=23
  

By using Slice Notation

• Slicing allows us to access a part of the list by specifying the index range.
• Slicing specifies the start and end index value along with colon[:] operator.
• Following is the syntax

List_name[start:stop[:step]]

• Where all start,stop and, step are integer values (either positive or negative).
• The result of slicing is a part of the list from the start index value to the stop index value.
• Sometimes, slicing includes only the start index but excludes the stop index.
• The step specifies the increment value of slicing.

For example
>>user_Age_lists=[33,40,55,21,43]
>>user_Age_lists[1:4]
[40,55,21]
>>user_Age_lists[:4]
[33,40,55,21]
>>user_Age_lists[2:]
[55,21,43]
>>user_Age_lists[1:5:2]
[40,21]
>>

The list() Function

• The list() function is used to create the list.
• Following is the syntax.

List_Name(sequence)

• Where the sequence is optional which can be a string, tuple, or list.

For example
>>Message = "welcome"
>>List_name=list(Message)
['w','e','l','c','o','m','e']
>>

• If the sequence is not specified, then the empty list will be created.

Modify items in a list

• The list is mutable, so We can modify items in the list by replacing old vale with new value.
• Following is the syntax to modify items in a list.

List_name[index of item to be modified]= new_value

For Example

>>fruits =['mango ',' fig',' banana']
>>fruits[1]= 'apple'
>>fruits
['mango',' apple',' banana']
>>

Add an item to the list

• We can add a new item to the list by using the append() function.
• For example, If we want to add fig to the Fruits list. we can execute the following code

>>fruits.append('fig')
>>

• The append() function will add the item to the end of the list. Now the list is.

>>fruits
[ 'mango',' apple ',' banana',' fig']
>>

Remove items from the list

• We can remove the item from the list by using the del statement.
• Syntax of del statement is

del list_name[index of the item to be deleted]

• For example, we want to delete the banana from fruits list.

>>del fruits[2]
>>

• After executing the above statement, your list becomes.

>>fruits
[ 'mango ',' apple ',' fig']
>>

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