Operators, Expression Evaluation, and Comments

1. Operator Types in Python

Arithmetic Operators

• Used for mathematical operations.

• + (Addition), - (Subtraction), * (Multiplication), / (Division), // (Floor Division), % (Modulus), ** (Exponentiation)

• Example:

  a = 10
  b = 3
  print(a + b)  # 13
  print(a / b)  # 3.333...
  print(a // b) # 3
  print(a ** b) # 1000
  

Relational (Comparison) Operators

• Compare values and return True or False.

• ==, !=, >, <, >=, <=

• Example:

  print(5 > 2)   # True
  print(5 == 2)  # False
  

Logical Operators

• Combine conditional statements.

• and, or, not

• Example:

  x = 5
  print(x > 2 and x < 10)  # True
  print(not(x == 5))       # False
  

Bitwise Operators

• Perform operations on binary representations.

• & (AND), | (OR), ^ (XOR), ~ (NOT), << (Left Shift), >> (Right Shift)

• Example:

  a = 5  # 0101
  b = 3  # 0011
  print(a & b)  # 1
  print(a | b)  # 7
  print(a ^ b)  # 6
  print(~a)     # -6
  print(a << 1) # 10
  print(a >> 1) # 2
  

Assignment Operators

• Assign values to variables.

• =, +=, -=, *=, /=, //=, %=, **=, &=, |=, ^=, >>=, <<=

• Example:

  x = 10
  x += 5  # x = x + 5
  print(x)  # 15
  

Membership Operators

• Test membership in a sequence (like list, string, tuple).

• in, not in

• Example:

  nums = [1, 2, 3]
  print(2 in nums)      # True
  print(4 not in nums)  # True
  

Identity Operators

• Compare memory locations of two objects.

• is, is not

• Example:

  a = [1, 2]
  b = a
  c = [1, 2]
  print(a is b)      # True
  print(a is c)      # False
  print(a == c)      # True
  

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2. Expression Evaluation, Precedence & Associativity

• Precedence: Determines the order in which operators are evaluated in an expression.

• Associativity: Determines the direction (left-to-right or right-to-left) in which operators of the same precedence are evaluated.

• Parentheses ``()`` can be used to override the default precedence and make expressions clearer.

Operator Precedence Table in Python

Python Operator Precedence

Precedence Level	Operators	Description	Associativity
1 (Highest)	()	Parentheses (grouping)	Left-to-right
2	**	Exponentiation	Right-to-left
3	+x, -x, ~x	Unary plus, minus, bitwise NOT	Right-to-left
4	*, /, //, %	Multiplication, division, modulus	Left-to-right
5	+, -	Addition, subtraction	Left-to-right
6	<<, >>	Bitwise shift	Left-to-right
7	&	Bitwise AND	Left-to-right
8	^	Bitwise XOR	Left-to-right
9	|	Bitwise OR	Left-to-right
10	==, !=, >, <, >=, <=, is, is not, in, not in	Comparisons, identity, membership	Left-to-right
11	not	Logical NOT	Right-to-left
12	and	Logical AND	Left-to-right
13	or	Logical OR	Left-to-right
14 (Lowest)	=, +=, -=, *=, /=, //=, %=, **=, &=, |=, ^=, >>=, <<=	Assignment operators	Right-to-left

Examples

result = 2 + 3 * 4      # Multiplication has higher precedence: 2 + (3 * 4) = 14
result = (2 + 3) * 4    # Parentheses change the order: (2 + 3) * 4 = 20
result = 2 ** 3 ** 2    # Exponentiation is right-to-left: 2 ** (3 ** 2) = 512
result = 10 - 4 + 2     # Addition and subtraction are left-to-right: (10 - 4) + 2 = 8

• Tip: When in doubt, use parentheses to clarify the intended order of evaluation.

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3. Comments in Python

Single-line Comments

• Start with #.

• Example:

  # This is a single-line comment
  print("Hello")  # This is an inline comment
  

Multi-line Comments

• Use multiple # lines or triple quotes (''' or """).

• Example:

  # This is a
  # multi-line comment
  
  '''
  This is also a
  multi-line comment
  '''
  

• Tip: Use comments to explain code logic, especially for complex sections.

Docstrings

• Use triple quotes (''' or """) to create docstrings for modules, classes, and functions.

• Example:

  def add(a, b):
      """
      Adds two numbers.
      """
      return a + b
  

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Prepared by Zaid Kamil.