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Lists

Lists are ordered, mutable sequences that can store any type of element.

Python Lists

Lists are one of Python's most versatile data structures. They are ordered, mutable (changeable), and can contain duplicate values of any type.

Creating Lists

Lists are defined with square brackets [].

List Methods

append(), insert(), remove(), pop(), sort(), reverse(), clear(), copy(), extend(), index(), count()

Syntax

<pre><code># Creating lists
fruits = ["apple", "banana", "cherry"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", True, 3.14]
empty = []

# Indexing (0-based)
print(fruits[0])   # apple
print(fruits[-1])  # cherry (last element)

# Slicing
print(fruits[0:2])  # ['apple', 'banana']
print(fruits[::-1]) # Reversed list

# Modifying
fruits[0] = "mango"    # Change element
fruits.append("grape") # Add to end
fruits.insert(1, "kiwi") # Insert at index
fruits.remove("banana")  # Remove by value
popped = fruits.pop()    # Remove and return last

# Useful operations
print(len(fruits))       # Length
print("mango" in fruits) # Membership test
fruits.sort()            # Sort in place
fruits.reverse()         # Reverse in place
sorted_copy = sorted(fruits) # Returns new sorted list

# List comprehension (preview)
squares = [x**2 for x in range(10)]
</code></pre>

Revision Notes

• [] creates a list; mutable (can change)
• 0-indexed; negative index from end
• append() adds to end; insert(i, x) at position
• remove(x) by value; pop(i) by index
• sort() in-place; sorted() returns new list
• len(), in, not in work on lists

List Statistics

Medium

Write a function that takes a list of numbers and returns a dictionary with:
- min: minimum value
- max: maximum value
- sum: total sum
- avg: average (rounded to 2 decimal places)
- count: number of elements

Input:

[4, 7, 2, 9, 1, 5]

Output:

{"min": 1, "max": 9, "sum": 28, "avg": 4.67, "count": 6}

Show Hint

Python has built-in min(), max(), sum(), and len() functions.

Solve this Challenge

Show Solution

def list_stats(numbers):
    return {
        "min": min(numbers),
        "max": max(numbers),
        "sum": sum(numbers),
        "avg": round(sum(numbers) / len(numbers), 2),
        "count": len(numbers)
    }

numbers = [4, 7, 2, 9, 1, 5]
result = list_stats(numbers)
print(result)

Tuples