Python Lists: Nested Structures and List Comprehensions Explained

The note introduces Python list fundamentals, starting with one‑dimensional, two‑dimensional and three‑dimensional list definitions and demonstrates how to access elements using index notation.

list1 = [12,34,54,65,7]  # one‑dimensional list
print(list1[3])          # → 65

list2 = [32,4,545,6,["hello",434,6565,78],44343]  # two‑dimensional list
print(list2[4][2])      # → 6565

list3 = [44,45,6,7,[43,53,57,[63,74,83,25,64]],56,97]  # three‑dimensional list
print(list3[4][3][3])   # → [63,74,83,25,64]

Next, the author explains list comprehensions by first showing the explicit creation of a list of integers 1‑10 and then converting the same range with list(range(1,11)). A loop‑based method for generating squares 1‑5 is presented, followed by the equivalent comprehension syntax.

list4 = [i**2 for i in range(1,6)]
print(list4)  # → [1,4,9,16,25]

Additional comprehensions illustrate filtering: extracting odd numbers from 1‑10 and further selecting numbers that are both odd and divisible by 3.

list5 = [i for i in range(1,11) if i % 2 == 1]
print(list5)  # → [1,3,5,7,9]

list6 = [i for i in range(1,11) if i % 2 == 1 and i % 3 == 0]
print(list6)  # → [3,9]

All example outputs are shown, confirming the correct behavior of nested indexing and comprehension filters.