Python list

List & Tuple Data in Python
Prof. K. Adisesha| 1
Python Lists
Python Collections (Arrays)
There are four collection data types in the Python programming language:
 List is a collection, which is ordered and changeable. Allows duplicate members.
 Tuple is a collection, which is ordered and unchangeable. Allows duplicate members.
 Set is a collection, which is unordered and unindexed. No duplicate members.
 Dictionary is a collection, which is unordered, changeable and indexed. No duplicate
members.
When choosing a collection type, it is useful to understand the properties of that type. Choosing
the right type for a particular data set could mean retention of meaning, and, it could mean an
increase in efficiency or security.
List: A list is a collection, which is ordered and changeable. In Python, lists are written with
square brackets.
Example
Create a List:
StuList = ["Prajwal", "Sunny", "Rekha"]
print(StuList)
Output: ['Prajwal', 'Sunny', 'Rekha']
Access Items: You access the list items by referring to the index number:
Example
Print the second item of the list:
print(StuList[1])
Output: Sunny
Negative Indexing: Negative indexing means beginning from the end, -1 refers to the last item,
-2 refers to the second last item etc.
Example
Print the last item of the list:
print(StuList[-1])
Output: Rekha
Range of Indexes: You can specify a range of indexes by specifying start and end position of the
range.
 When specifying a range, the return value will be a new list with the specified items.
Example
Return the third, fourth, and fifth item:
StuList = ["Prajwal", "Sunny", "Rekha", "Sam", "Adi", "Ram", "Shilu"]
print(StuList[2:5])

Output: ["Rekha", "Sam", "Adi"]
Note: The search will start at index 2 (included) and end at index 5 (not included).
Range of Negative Indexes: Specify negative indexes if you want to start the search from the end
of the list:
Example
This example returns the items from index -4 (included) to index -1 (excluded)
StuList = ["Prajwal", "Sunny", "Rekha", "Sam", "Adi", "Ram", "Shilu"]
print(StuList[-4:-1])
Output: ["Sam", "Adi", "Ram"]
Change Item Value: To change the value of a specific item, refer to the index number:
Example
Change the second item:
StuList[1] = "Adi"
print(StuList)
Output: ["Prajwal", "Adi", "Rekha"]
Loop through a List: You can loop through the list items by using a for loop:
Example
Print all items in the list, one by one:
for x in StuList:
print(x)
Output: Prajwal
Sunny
Rekha
Check if Item Exists: To determine if a specified item is present in a list use the in keyword:
Example
Check if “Sunny” is present in the list:
if "Prajwal" in StuList:
print("Yes, 'Sunny' is in the Student list")
Output: Yes, 'Sunny' is in the Student list
List Length
len() method: To determine how many items a list has use the:
Example
Print the number of items in the list:
print(len(StuList))
Output: 3

Add Items: To add an item to the end of the list, use the append), insert(), method:
 Using the append() method to append an item:
Example
StuList.append("Sam")
print(StuList)
Output: ['Prajwal', 'Sunny', 'Rekha', 'Sam']
 To add an item at the specified index, use the insert() method:
Example
Insert an item as the second position:
StuList.insert(1, "Sam")
print(StuList)
Output: ['Prajwal', 'Sam', 'Sunny', 'Rekha']
Remove Item: There are several methods to remove items from a list using: remove(), pop(), del,
clear()
 The remove() method removes the specified item:
Example
StuList.remove("Sunny")
print(StuList)
Output: ['Prajwal', 'Rekha']
 The pop() method removes the specified index, (or the last item if index is not specified):
Example
StuList.pop()
print(StuList)
Output: ['Prajwal', 'Sunny']
 The del keyword removes the specified index:
Example
del StuList[0]
print(StuList)
Output: ['Sunny', 'Rekha']
 The del keyword can also delete the list completely:
Example
del StuList

 The clear() method empties the list:
Example
StuList.clear()
print(StuList)
Copy a List: You cannot copy a list simply by typing list2 = list1, because: list2 will only be a
reference to list1, and changes made in list1 will automatically also be made in list2.
There are ways to make a copy, one-way is to use the built-in copy(), list() method.
 copy() method: Make a copy of a list:
Example
mylist = StuList.copy()
print(mylist)
 list() method: Make a copy of a list:
Example
mylist = list(StuList)
print(mylist)
Join Two Lists: There are several ways to join, or concatenate, two or more lists in Python.
 One of the easiest ways are by using the + operator.
Example
list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]
list3 = list1 + list2
print(list3)
Output: ['a', 'b', 'c', 1, 2, 3]
Another way to join two lists are by appending all the items from list2 into list1, one by one:
Example
Append list2 into list1:
list1 = ["a", "b”, "c"]
list2 = [1, 2, 3]
for x in list2:
list1.append(x)
print(list1)
Output: ['a', 'b', 'c', 1, 2, 3]
 Use the extend() method, which purpose is to add elements from one list to another list:
Example

Use the extend() method to add list2 at the end of list1:
list1 = ["a", "b”, "c"]
list2 = [1, 2, 3]
list1.extend(list2)
print(list1)
Output: ['a', 'b', 'c', 1, 2, 3]
The list() Constructor: It is also possible to use the list() constructor to make a new list.
Example
Using the list() constructor to make a List:
StuList = list(("Prajwal", "Sunny", "Rekha")) # note the double round-brackets
print(StuList)
List Methods
Python has a set of built-in methods that you can use on lists.
Method Description
append() Adds an element at the end of the list
clear() Removes all the elements from the list
copy() Returns a copy of the list
count() Returns the number of elements with the specified value
extend() Add the elements of a list (or any iterable), to the end of the current list
index() Returns the index of the first element with the specified value
insert() Adds an element at the specified position
pop() Removes the element at the specified position
remove() Removes the item with the specified value
reverse() Reverses the order of the list
sort() Sorts the list

Python Tuples
A tuple is a collection, which is ordered and unchangeable. In Python, tuples are written with
round brackets.
Example
Create a Tuple:
Stu_tuple = (“Prajwal”, “Sunny”, “Rekha”)
print(Stu_tuple)
Output: ('Prajwal', 'Sunny', 'Rekha')
Access Tuple Items: Tuple items access by referring to the index number, inside square
brackets:
Example
Print the second item in the tuple:
print(Stu_tuple[1])
Output: Sunny
Negative Indexing: Negative indexing means beginning from the end, -1 refers to the last item,
and -2 refers to the second last item etc.
Example
Print the last item of the tuple:
print(Stu_tuple[-1])
Output: Rekha
Range of Indexes: You can specify a range of indexes by specifying start and end of the range.
When specifying a range, the return value will be a new tuple with the specified items.
Example
Return the third, fourth, and fifth item:
Stu_tuple = ("Prajwal", "Sunny", "Rekha", "Sam", "Adi", "Ram", "Shilu")
print(Stu_tuple[2:5])
Output: (“Rekha", "Sam", "Adi”)
Note: The search will start at index 2 (included) and end at index 5 (not included).
Range of Negative Indexes: Specify negative indexes if you want to start the search from the end
of the tuple:
Example
This example returns the items from index -4 (included) to index -1 (excluded)
Stu_tuple = ("Prajwal", "Sunny", "Rekha", "Sam", "Adi", "Ram", "Shilu")
print(Stu_tuple[-4:-1])
Output: ("Sam", "Adi", "Ram")

Change Tuple Values: Once a tuple is created, you cannot change its values. Tuples are
unchangeable or immutable as it also is called. However, by converting the tuple into a list, change
the list, and convert the list back into a tuple.
Example
Convert the tuple into a list to be able to change it:
x = (“Prajwal”, “Sunny”, “Rekha”)
y = list(x)
y[1] = "Adi"
x = tuple(y)
print(x)
Output: (“Prajwal”, “Adi”, “Rekha”)
Loop through a Tuple: You can loop through the tuple items by using a for loop.
Example
Iterate through the items and print the values:
for x in Stu_tuple:
print(x,”t”)
Output: Prajwal Sunny Rekha
Check if Item Exists: To determine if a specified item is present in a tuple use the in keyword:
Example
Check if "Prajwal" is present in the tuple:
if "Prajwal" in Stu_tuple:
print("Yes, 'Prajwal' is in the Student tuple")
Output: Yes, 'Prajwal' is in the Student tuple
Tuple Length: To determine how many items a tuple has, use the len() method:
Example
Print the number of items in the tuple:
print(len(Stu_tuple))
Output: 3
Adding Items: Once a tuple is created, you cannot add items to it. Tuples are unchangeable.
Example
You cannot add items to a tuple:
Stu_tuple[3] = "Adi" # This will raise an error
print(Stu_tuple) Output: TypeError: 'tuple' object does not support item assignment
Create Tuple With One Item: To create a tuple with only one item, you have add a comma
after the item, unless Python will not recognize the variable as a tuple.

Example
One item tuple, remember the comma:
Stu_tuple = ("Prajwal",)
print(type(Stu_tuple))
Stu_tuple = ("Prajwal") #NOT a tuple
print(type(Stu_tuple))
Output: <class 'tuple'>
<class 'str'>
Remove Items: Tuples are unchangeable, so you cannot remove items from it, but you can delete
the tuple completely:
Example
The del keyword can delete the tuple completely:
del Stu_tuple
print(Stu_tuple) #this will raise an error because the tuple no longer exists
Join Two Tuples: To join two or more tuples you can use the + operator:
Example
Join two tuples:
tuple1 = ("a", "b" , "c")
tuple2 = (1, 2, 3)
tuple3 = tuple1 + tuple2
print(tuple3)
Output: ('a', 'b', 'c', 1, 2, 3)
The tuple() Constructor: It is also possible to use the tuple() constructor to make a tuple.
Example
Using the tuple() method to make a tuple:
Stu_tuple = tuple((“Prajwal”, “Sunny”, “Rekha”)) # note the double round-brackets
print(Stu_tuple)
Output: ('Prajwal', 'Sunny', 'Rekha')
Tuple Methods
Python has two built-in methods that you can use on tuples.
Method Description
count() Returns the number of times a specified value occurs in a tuple
index() Searches the tuple for a specified value and returns the position of where it
was found

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