Python programming

List

Transcript

1. PYTHON LIST Notes, Characteristics, Creation & List Operations fruits = ['apple', 'banana', 'cherry'] Teaching Presentation • Simple examples for students
2. 1. What is a Python List? A list is a built-in Python data structure used to store an ordered collection of items. A list can contain items of different data types. Lists are changeable (mutable), so items can be added, removed, or modified. Lists are written using square brackets [ ]. fruits = ['apple', 'banana', 'cherry'] print(fruits) 2
3. 2. Key Characteristics of Python List 1. Ordered – items maintain a defined order. 2. Changeable (Mutable) – elements can be added, removed, or changed. 3. Allows Duplicates – the same value can occur more than once. 4. Indexed – elements use zero-based indexing. 5. Heterogeneous – different data types can be stored in one list. 3
4. 3. Creating a List Empty list: my_list = [] List with numbers: numbers = [1, 2, 3, 4, 5] List with strings: fruits = ['apple', 'banana', 'cherry'] Mixed data types: mixed_list = ['hello', 123, True, 3.14] Nested list: nested_list = [[1, 2], [3, 4], ['a', 'b']] Using list() constructor: another_list = list(('one', 'two', 'three')) 4
5. 4. Accessing List Elements fruits = ['apple', 'banana', 'cherry'] # Zero-based indexing print(fruits[0]) # apple print(fruits[1]) # banana print(fruits[2]) # cherry # Negative indexing (from the end) print(fruits[-1]) # cherry print(fruits[-2]) # banana Remember: first element has index 0. Negative index -1 refers to the last element. 5
6. 5. Modifying List Elements fruits = ['apple', 'banana', 'cherry'] fruits[1] = 'orange' print(fruits) # Output: ['apple', 'orange', 'cherry'] Use the index and assignment operator (=) to change an existing element. 6
7. 6. Adding Elements to a List append() – adds one element at the end. insert() – adds an element at a specified index. extend() – adds elements from another iterable, such as another list. fruits = ['apple', 'banana'] fruits.append('cherry') # ['apple', 'banana', 'cherry'] fruits.insert(1, 'grape') # ['apple', 'grape', 'banana', 'cherry'] more_fruits = ['mango', 'kiwi'] fruits.extend(more_fruits) # ['apple', 'grape', 'banana', 'cherry', 'mango', 'kiwi'] 7
8. 7. Removing Elements from a List remove(value) – removes the first occurrence of the specified value. pop(index) – removes and returns the element at the given index. If no index is given, it removes the last element. del – deletes an element at a specified index. clear() – removes all elements from the list. fruits = ['apple', 'grape', 'banana', 'cherry'] fruits.remove('grape') removed_item = fruits.pop(1) del fruits[0] fruits.clear() # [] print(fruits) 8
9. 8. Other Useful List Operations len(list) – returns the number of elements. count(value) – counts how many times a value occurs. index(value) – returns the index of the first occurrence. sort() – arranges the list in ascending order. reverse() – reverses the order of elements. nums = [3, 1, 4, 2] print(len(nums)) print(nums.count(3)) print(nums.index(4)) nums.sort() nums.reverse() # 4 # 1 # 2 # [1, 2, 3, 4] # [4, 3, 2, 1] 9
10. 9. Complete Example Program fruits = ['apple', 'banana', 'cherry'] fruits.append('orange') fruits.insert(1, 'grape') fruits[2] = 'mango' fruits.remove('banana') last = fruits.pop() print("List:", fruits) print("Removed last item:", last) # Output: # List: ['apple', 'grape', 'mango', 'cherry'] # Removed last item: orange 10
11. 10. Summary A list stores an ordered collection of items. Lists are mutable, so their contents can be changed. Lists allow duplicate values and different data types. Elements are accessed using zero-based indexing. append(), insert(), extend() are used to add elements. remove(), pop(), del, clear() are used to remove elements. len(), count(), index(), sort(), reverse() help manage lists. 11
12. 11. Practice Questions 1. Create a list of your 5 favorite movies. 2. Add a new movie to the list. 3. Insert a movie at the second position. 4. Change the third movie in the list. 5. Remove a movie by its name. 6. Remove the last movie using pop(). 7. Sort the list alphabetically. 8. Print the final list. 12