keip104

Introduction to Lists

• Definition: Lists in Python are mutable ordered sequences consisting of elements of one or more data types.

• Characteristics:

  • Enclosed in square brackets [].

  • Elements are separated by commas.

  • Can contain mixed data types (e.g., integers, floats, strings, tuples, other lists).

• Example:

  # List of even numbers
  list1 = [2, 4, 6, 8, 10, 12]
  print(list1)  # Output: [2, 4, 6, 8, 10, 12]

Accessing Elements in a List

• Indexing:

  • Lists are indexed starting from 0.

  • Use square brackets [] with the index to access elements.

  • Example:

    list1 = [2, 4, 6, 8, 10, 12]
    print(list1[0])  # Output: 2  (first element)
    print(list1[3])  # Output: 8  (fourth element)

• Negative Indexing: Access from the end of the list using negative indices.

Lists are Mutable

• Meaning: Contents of a list can be changed after creation.

• Example:

  list1 = ['Red', 'Green', 'Blue', 'Orange']
  list1[3] = 'Black'
  print(list1)  # Output: ['Red', 'Green', 'Blue', 'Black']

List Operations

1. Concatenation

• Combine lists using the + operator.

• Example:

  list1 = [1, 3, 5, 7, 9]
  list2 = [2, 4, 6, 8, 10]
  list3 = list1 + list2  # Output: [1, 3, 5, 7, 9, 2, 4, 6, 8, 10]

2. Repetition

• Use * for replicating list elements.

• Example:

  list1 = ['Hello']
  print(list1 * 4)  # Output: ['Hello', 'Hello', 'Hello', 'Hello']

3. Membership

• Check presence using in and not in operators.

• Examples:

  list1 = ['Red', 'Green', 'Blue']
  print('Green' in list1)  # Output: True
  print('Cyan' not in list1)  # Output: True

4. Slicing

• Create new lists from existing lists by slicing.

• Example:

  list1 = ['Red', 'Green', 'Blue', 'Cyan', 'Magenta', 'Yellow']
  print(list1[2:5])  # Output: ['Blue', 'Cyan', 'Magenta']

Traversing a List

• Use loops to access list elements.

• For Loop Example:

  for item in list1:
      print(item)

List Methods and Built-in Functions

• Common Methods:

  • len(): Returns number of elements.

  • append(): Add items to the end.

  • extend(): Add multiple items.

  • insert(): Insert at specific position.

  • remove(): Remove first occurrence.

  • pop(): Remove item at specified position.

  • sort(): Sort elements in place.

  • reverse(): Reverses the list order.

Example of List Method Usage

• 
  

  myList = [10, 20, 30]
  myList.append(40)
  myList.sort()  # Sorts the list
  print(myList)  # Output: [10, 20, 30, 40]

Introduction to Dictionaries

• Definition: Dictionaries are mutable mappings of key-value pairs.

• Characteristics:

  • Unordered collection of items.

  • Keys must be unique and immutable.

  • Values can be of any data type.

• Creating a Dictionary:

dict1 = {'Mohan': 95, 'Ram': 89}

- **Accessing Items**: Access values using their corresponding keys.
- **Example**:
  ```python
dict1['Mohan']  # Output: 95

Manipulating Dictionaries

• Adding items:

dict1['Suhel'] = 92

- Modifying existing items:
  ```python
dict1['Ram'] = 90