Chapter 2: Introduction to Python Lists

🔹 1. List

• A collection of elements (numbers, strings, etc.)

fruits = ["apple", "banana", "cherry"]

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🔹 2. Subset of List (Indexing)

• Accessing a single element using its index

print(fruits[1])    # Output: "banana"
print(fruits[-1])   # Output: "cherry"

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🔹 3. Slicing

• Extracting a portion (sublist) using a range of indices

print(fruits[0:2])  # Output: ["apple", "banana"]
print(fruits[1:])   # Output: ["banana", "cherry"]
print(fruits[:2])   # Output: ["apple", "banana"]

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🔹 4. Subset Slicing (Nested List)

• Access part of an inner list or string inside a list

nested = [["room", 10], ["hall", 12]]
print(nested[0][0])      # Output: "room"
print(nested[0][0][1:])  # Output: "oom" → slicing string inside list

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🔹 5. Referencing vs Copying

• Referencing: changing one affects the other

a = [1, 2, 3]
b = a
b[0] = 100
print(a)  # Output: [100, 2, 3] – both point to same list

• Copying: use slicing or copy()

c = a[:]     # or c = a.copy()
c[0] = 50
print(a)     # Output: [100, 2, 3]
print(c)     # Output: [50, 2, 3]

🔹 6. List Concatenation

• Adding elements to a list using the + operator creates a new list.

✅ Step-by-step Explanation:

areas = ["hallway", 11.25, "kitchen", 18.0, "chill zone", 20.0,
         "bedroom", 10.75, "bathroom", 10.50]

• This is your original list with alternating room names and their sizes.

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areas_1 = areas + ["poolhouse", 24.5]

• A new list areas_1 is created by adding "poolhouse" and its area 24.5 to the end of areas.

• areas remains unchanged (since + creates a copy).

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areas_2 = areas_1 + ["garage", 15.45]

• Another new list areas_2 is created by adding "garage" and its area 15.45 to areas_1.

• Again, this doesn't modify areas_1.

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🔹 7. List Growth Through Concatenation

• Each time, a new list is created, so:

  • areas: original list

  • areas_1: original + poolhouse

  • areas_2: areas_1 + garage

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✅ Summary Table:

🔹 8. BUILT IN PYTHON FUNCTIONS