List in Python

A list in Python is a collection used to store multiple items in a single variable.

• Lists are mutable, their elements can be modified after creation.
• Lists are defined using square brackets [ ], and values are separated by commas.
• Lists can hold different data types: integers, floats, strings, or even other lists.

Creating a List

Example:

nums = [25, 12, 36, 95, 14]
print(nums)   # [25, 12, 36, 95, 14]

Accessing Elements:

• List elements can be accessed using indexing (index starts at 0).
• If the list size is n, valid index values range from 0 to n-1.
• Negative indexing is also allowed (just like strings).

print(nums[0])   # 25
print(nums[4])   # 14
print(nums[-1])  # 14
print(nums[-5])  # 25

If an index is out of range, Python raises an IndexError:

print(nums[54])  
# IndexError: list index out of range

Slicing a List:

print(nums[2:])    # [36, 95, 14]
print(nums[:3])    # [25, 12, 36]

Different Types of Lists

1. List of String

print(nums[2:])    # [36, 95, 14]
print(nums[:3])    # [25, 12, 36]

2. List of Mixed Data Types

values = [9.5, 'Navin', 25]
print(values)   # [9.5, 'Navin', 25]

3. List of Lists (Nested Lists)

mil = [nums, names]
print(mil)  
# [[25, 12, 36, 95, 14], ['navin', 'kiran', 'john']]

List Methods and Operations

(a) Adding Elements

• append() → adds a single value to the end of the list.

nums.append(45)
print(nums)   # [25, 12, 36, 95, 14, 45]

• insert(index, value) → inserts a value at a specific position.

nums.insert(2, 77)
print(nums)   # [25, 12, 77, 36, 95, 14, 45]

• extend(list) → adds multiple values at once.

nums.extend([29, 12, 14, 36])
print(nums)   # [25, 12, 77, 36, 95, 14, 45, 29, 12, 14, 36]

(b) Removing Elements

• remove(value) → removes the first occurrence of a value.

nums.remove(14)
print(nums)   # [25, 12, 77, 36, 95, 45]

• pop(index) → removes element at the given index and returns it.

nums.pop(1)    # returns 12
print(nums)    # [25, 77, 36, 95, 45]

• pop() without index → removes and returns the last element.

nums.pop()     # returns 45

• del list[start:end] → deletes a sublist.

del nums[2:]
print(nums)    # [25, 77]

• clear() → removes all elements from the list.

nums.clear()
print(nums)   # []

(c) Sorting and Ordering

• sort() → sorts the list in ascending order.

nums = [25, 77, 29, 12, 14, 36]
nums.sort()
print(nums)   # [12, 14, 25, 29, 36, 77]

Built-in Functions with Lists

• min(list) → returns the smallest element.

min(nums)   # 12

• max(list) → returns the largest element.

max(nums)   # 77

• sum(list) → returns the sum of all elements.

sum(nums)   # 193