Python Lists

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Python Lists

A list in Python is an ordered, changeable collection of items. Lists can contain elements of different data types, including numbers, strings, and other lists.

Creating a list:
Example:
my_list = [1, 2, 3, 4]
fruits = ["apple", "banana", "cherry"]
mixed = [1, "apple", 3.5]

Accessing elements:
Use the index to access items. Indexing starts from 0.
Example:
print(fruits[0]) # apple
print(fruits[-1]) # cherry (last item)

Slicing a list:
Get a sublist using a range of indexes.
Example:
print(fruits[0:2]) # ['apple', 'banana']
print(fruits[:2]) # ['apple', 'banana']
print(fruits[1:]) # ['banana', 'cherry']

Changing elements:
Lists are mutable, so you can change items.
Example:
fruits[1] = "blueberry"
print(fruits) # ['apple', 'blueberry', 'cherry']

Adding elements:

• append(): adds an item at the end
  Example:
  fruits.append("orange")

• insert(): adds an item at a specific position
  Example:
  fruits.insert(1, "kiwi")

Removing elements:

• remove(): removes first matching value
  Example:
  fruits.remove("apple")

• pop(): removes item at index (default last)
  Example:
  fruits.pop()

• del: removes item or whole list
  Example:
  del fruits[0]
  del fruits

List length:
Use len() to get the number of items.
Example:
len(fruits)

Iterating through a list:
Use a for loop to access each item.
Example:
for fruit in fruits:
print(fruit)

Checking existence of an element:
Use in to check if an item exists.
Example:
if "apple" in fruits:
print("Found")

List methods:

• sort(): sorts the list in ascending order

• reverse(): reverses the list

• copy(): creates a copy of the list

• clear(): removes all items

• count(): returns number of occurrences of a value

• extend(): adds elements from another list
  Example:
  numbers = [3, 1, 4, 2]
  numbers.sort()
  numbers.reverse()

Nested lists:
Lists can contain other lists.
Example:
matrix = [[1,2,3], [4,5,6], [7,8,9]]
print(matrix[0][1]) # 2