Creating a list Basic List operations Indexing and slicing in Lists Built-in functions used on lists List methods The del statement

1. Python Programming-Part 6
Megha V
Research Scholar
Kannur University
15-11-2021 meghav@kannuruniv.ac.in 1

2. Difference between Method and Function in Python
Function
• A function is a block of code to carry out a specific task, will contain
its own scope and is called by name.
• All functions may contain zero(no) arguments or more than one
arguments.
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3. Difference between Method and Function in Python
Method
• A method in python is somewhat similar to a function, except it is
associated with object/classes.
• Methods in python are very similar to functions except for two major
differences.
• The method is implicitly used for an object for which it is called.
• The method is accessible to data that is contained within the class.
15-11-2021 meghav@kannuruniv.ac.in 3

4. List
• Creating a list
• Basic List operations
• Indexing and slicing in Lists
• Built-in functions used on lists
• List methods
• The del statement
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5. List
• Creating a list
• Lists are used to store multiple items in a single variable.
thislist = ["apple", "banana", "cherry"]
print(thislist)
• We can update lists by using slice[] on the LHS of the assignment operator
Eg:
list=[‘bcd’,147,2.43,’Tom’]
print(“Item at index 2=”,list[2])
list[2]=500
print(“Item at index 2=”,list[2])
Output
2.43
500
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6. List
• To remove an item from a list
• del statement
• remove() method
list=[‘abcd’,147,2.43,’Tom’,74.9]
print(list)
del list[2]
print(“list after deletion:”, list)
Output
[‘abcd’,147,2.43,’Tom’,74.9]
list after deletion:[‘abcd’,147,’Tom’,74.9]
15-11-2021 meghav@kannuruniv.ac.in 6

7. • The del keyword can also used to delete the list completely
thislist = ["apple", "banana", "cherry"]
del thislist
• remove()function
thislist = ["apple", "banana", "cherry"]
thislist.remove("banana")
print(thislist)
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8. Built-in list functions
1. len(list) – Gives the total length of list
2. max(list)- Returns item from list with maximum value
3. min(list)- Returns item from list with minimum value
4. list(seq)- Returns a tuple into a list
5. map(aFunction,aSequence) – Apply an operation to each item and
collect result.
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9. Example
list1=[1200,147,2.43,1.12]
list2=[213,100,289]
print(list1)
print(list2)
print(len(list1))
print(“Maximum value in list1 is ”,max(list))
print(“Maximum value in list2 is ”,min(list))
Output
[1200,147,2.43,1.12]
[1200,147,2.43,1.12]
4
Maximum value in the list1 is 1200
Minimum value in the list2 is 100
15-11-2021 meghav@kannuruniv.ac.in 9

10. Example of list() and map() function
tuple = (‘abcd’,147,2.43,’Tom’)
print(“List:”,list(tuple))
str=input(“Enter a list(space separated):”)
lis=list(map(int,str.split()))
print(lis)
Output
List: [‘abcd’,147,2.43,’Tom’]
Enter a list (space separated) : 5 6 8 9
[5,6,8,9]
In this example a string is read from the keyboard and each item is
converted into int using map() function
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11. Built-in list methods
1. list.append(obj) –Append an object obj passed to the existing list
list = [‘abcd’,147,2.43,’Tom’]
print(“Old list before append:”, list)
list.append(100)
print(“New list after append:”,list)
Output
Old list before append: [‘abcd’,147,2.43,’Tom’]
New list after append: [‘abcd’,147,2.43,’Tom’,100]
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12. 2. list.count(obj) –Returns how many times the object obj appears in a list
list = [‘abcd’,147,2.43,’Tom’]
print(“The number of times”,147,”appears in the
list=”,list.count(147))
Output
The number of times 147 appears in the list = 1
15-11-2021 meghav@kannuruniv.ac.in 12

13. 3. list.remove(obj) – Removes an object
list1 = [‘abcd’,147,2.43,’Tom’]
list.remove(‘Tom’)
print(list1)
Output
[‘abcd’,147,2.43]
4. list.index(obj) – Returns index of the object obj if found
print(list1.index(2.43))
Output
2
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14. 5. list.extend(seq)- Appends the contents in a sequence passed to a list
list1 = [‘abcd’,147,2.43,’Tom’]
list2 = [‘def’,100]
list1.extend(list2)
print(list1)
Output
[‘abcd’,147,2.43,’Tom’,‘def’,100]
6. list.reverse() – Reverses objects in a list
list1.reverse()
print(list1)
Output
[‘Tom’,2.43,147,’abcd’]
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15. 7. list.insert(index,obj)- Returns a list with object obj inserted at the given index
list1 = [‘abcd’,147,2.43,’Tom’]
list1.insert(2,222)
print(“List after insertion”,list1)
Output
[‘abcd’,147,222,2.43,’Tom’]
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16. 8. list.sort([Key=None,Reverse=False]) – Sort the items in a list and returns the list,
If a function is provided, it will compare using the function provided
list1=[890,147,2.43,100]
print(“List before
sorting:”,list1)#[890,147,2.43,100]
list1.sort()
print(“List after sorting in ascending
order:”,list1)#[2.43,100,147,890]
list1.sort(reverse=True)
print(“List after sorting in descending
order:”,list1)#[890,147,100,2.43]
15-11-2021 meghav@kannuruniv.ac.in 16

17. 9.list.pop([index]) – removes or returns the last object obj from a list. we can pop out
any item using index
list1=[‘abcd’,147,2.43,’Tom’]
list1.pop(-1)
print(“list after poping:”,list1)
Output
List after poping: [‘abcd’,147,2.43]
10. list.clear() – Removes all items from a list
list1.clear()
11. list.copy() – Returns a copy of the list
list2=list1.copy()
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18. Using List as Stack
• List can be used as stack(Last IN First OUT)
• To add an item to the top of stack – append()
• To retrieve an item from top –pop()
stack = [10,20,30,40,50]
stack.append(60)
print(“stack after appending:”,stack)
stack.pop()
print(“Stack after poping:”,stack)
Output
Stack after appending:[10,20,30,40,50,60]
Stack after poping:[10,20,30,40,50]
15-11-2021 meghav@kannuruniv.ac.in 18

19. Using List as Queue
• List can be used as Queue data structure(FIFO)
• Python provide a module called collections in which a method called deque is designed to
have append and pop operations from both ends
from collections import deque
queue=deque([“apple”,”orange”,”pear”])
queue.append(“cherry”)#cherry added to right end
queue.append(“grapes”)# grapes added to right end
queue.popleft() # first element from left side is removed
queu.popleft() # first element in the left side removed
print(queue)
Output
deque([‘pear’,’cherry’,’grapes’])
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20. LAB ASSIGNMENTS
• Write a Python program to change a given string to a new string
where the first and last characters have been changed
• Write a Python program to read an input string from user and displays
that input back in upper and lower cases
• Write a program to get the largest number from the list
• Write a program to display the first and last colors from a list of color
values
• Write a program to Implement stack operation using list
• Write a program to implement queue operation using list
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