Importance of Comments: Improve code readability, explain complex logic, aid in maintenance, and help other developers understand the code.

17. Reserved Words and Indentation

Reserved Words (Keywords): Words with special meaning in Python, cannot be used as identifiers.
- Examples: False, None, True, and, as, assert, async, await, break, class, continue, def, del, elif, else, except, finally, for, from, global, if, import, in, is, lambda, nonlocal, not, or, pass, raise, return, try, while, with, yield.

Indentation: Python uses whitespace (spaces or tabs, conventionally 4 spaces) to define code blocks (e.g., inside if statements, loops, functions).

Importance: It's crucial for syntax; incorrect indentation causes IndentationError.


# Correct Indentation
if True:
    print("This is inside the if block.")
    x = 10
print("This is outside the if block.")

# Incorrect Indentation (will cause error)
# if True:
# print("Error: expected an indented block")

18. Operators and Expressions

Operators: Symbols that perform operations on values and variables.
Expressions: Combinations of values, variables, and operators that evaluate to a single value.
Categories:
- Arithmetic: +, -, *, / (true division), // (floor division), % (modulo), ** (exponentiation).
  - Example: result = 10 + 5 * 2 (evaluates to 20)
- Relational (Comparison): ==, !=, >, <, >=, <=. Return Boolean.
  - Example: is_equal = (5 == 5) (True)
- Logical: and, or, not. Combine Boolean expressions.
  - Example: condition = (True and False) (False)
- Assignment: =, +=, -=, *=, /=, etc. Assign values.
  - Example: x = 10; x += 5 (x becomes 15)
- Bitwise: & (AND), | (OR), ^ (XOR), ~ (NOT), << (left shift), >> (right shift). Operate on bits.
  - Example: 5 & 3 (1, binary 101 & 011 = 001)
- Membership: in, not in. Check if a value is present in a sequence.
  - Example: 'a' in 'apple' (True)
- Identity: is, is not. Check if two variables refer to the same object in memory.
  - Example: a = [1