List Manipulation Based on CBSE Curriculum Class 11

Introduction

• Python lists: containers for collections of values.
• Lists are mutable; values can be changed without creating a new list.
• Lists are sequences like strings and tuples but mutable.

List Creation

• Lists store values of any kind and are represented by square brackets [].
  • Examples:
    • []: Empty list
    • [1, 2, 3]: List of integers
    • [1, 2.5, 5.6, 9]: List of numbers (integers and floats)
    • [a, b, c]: List of characters
    • [a, 1, b, 3.5, zero]: Mixed values list
    • [one, two, three]: List of strings
• Creation methods:
  • L = []: Empty list
  • L = list(): Using the list() function
  • even = [0, 2, 4,..., 20]: Long list
  • L = [3, 4, [5, 6], 7]: Nested list
• Using eval(input()) to generate lists from user input.

Accessing a List

• Lists are sequences similar to strings and support indexing (forward and backward).
  • Forward indexing: From 0 to n-1
  • Backward indexing: From -n to -1
• Access methods:
  • len(): Returns the length of a list.
  • L[i]: Accesses value at index i.
  • L[i:j]: Returns a new list from index i to j-1.
• Membership operators in and not in function similarly as in other sequences.
• + operator joins lists, * operator repeats lists.*

Difference Between List and String

• Lists are mutable; strings are immutable.
• Values in a string cannot be changed, while values in a list can.

Traversal of a List

• Traversal involves accessing and processing each element.
• Achieved using a for loop.

Comparison of Lists

• Relational operators compare lists lexicographically.
• Types and elements must be similar for valid comparison.

List Operations

• Operations include joining (+), replicating (*), and slicing.
• List slicing syntax: seq = list[start:stop] or seq = list[start:stop:step].*

List Manipulation

• Appending: list.append(item).
• Updating: list[index] = new_value.
• Deletion:
  • del list[index] deletes an element.
  • del list deletes the entire list.
• pop() deletes and returns an element from a specified index.

List Functions and Methods

• List.index(item): Returns the index of an item.
• List.append(item): Adds item to the end.
• List.extend(list): Appends another list.
• List.insert(pos, item): Inserts item at position.
• List.pop(index): Removes and returns item at index.
• List.remove(value): Deletes first occurrence of a value.
• List.clear(): Empties the list.
• List.count(item): Counts occurrences of an item.
• List.reverse(): Reverses the list.
• List.sort(): Sorts the list; use list.sort(reverse=True) for descending order.

Important Notes

• Sorting won't work on lists containing complex numbers.
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Presented by: Neha Tyagi, KV 5 Jaipur II Shift