Python Expressions

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1. What is an Expression?

• An expression is a combination of values, variables, operators, and function calls that evaluates to a single value.
• Expressions can be as simple as a single variable or as complex as a combination of multiple operations.

x = 10                # Simple expression (variable assignment)
result = x + 5        # Expression with an operator
name = "Raj"          # String expression

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2. Components of Expressions

• Operands: Values or variables on which operations are performed.
• Operators: Symbols that perform operations on operands (e.g., +, -, *, /).

a = 5
b = 10
sum = a + b  # a and b are operands, + is the operator

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3. Types of Expressions

• Arithmetic Expressions: Perform mathematical operations.
  • Operators: +, -, *, /, //, %, **
  • Example:
    x = 10
    y = 3
    result = x ** 2 + y  # 10^2 + 3 = 103
    
• String Expressions: Combine or manipulate strings.
  • Operators: + (concatenation), * (repetition)
  • Example:
    first_name = "Raj"
    last_name = "Kumar"
    full_name = first_name + " " + last_name  # "Raj Kumar"
    greeting = "Hello, " * 3  # "Hello, Hello, Hello, "
    
• Comparison Expressions: Compare two values and return a Boolean (True or False).
  • Operators: ==, !=, >, <, >=, <=
  • Example:
    age_raj = 25
    age_ram = 30
    is_raj_older = age_raj > age_ram  # False
    
• Logical Expressions: Combine Boolean values using logical operators.
  • Operators: and, or, not
  • Example:
    is_student = True
    is_employed = False
    can_apply = is_student and not is_employed  # True
    
• Membership Expressions: Check if a value exists in a sequence (e.g., list, string).
  • Operators: in, not in
  • Example:
    names = ["Raj", "Ram", "Anand", "Bala"]
    is_karthik_present = "Karthik" in names  # False
    
• Identity Expressions: Check if two variables refer to the same object.
  • Operators: is, is not
  • Example:
    x = 10
    y = 10
    is_same = x is y  # True (for small integers, Python reuses memory)
    

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4. Additional Examples

• Arithmetic Expression:
  age_raj = 25
  age_ram = 30
  total_age = age_raj + age_ram  # 55
  
• String Expression:
  first_name = "Suresh"
  last_name = "Kumar"
  full_name = first_name + " " + last_name  # "Suresh Kumar"
  
• Comparison Expression:
  marks_anand = 85
  marks_bala = 90
  is_anand_higher = marks_anand > marks_bala  # False
  
• Logical Expression:
  is_karthik_student = True
  is_karthik_employed = False
  can_karthik_apply = is_karthik_student and not is_karthik_employed  # True
  
• Membership Expression:
  names = ["David", "Kannan", "Siva", "Ramesh"]
  is_sujatha_present = "Sujatha" in names  # False
  
• Identity Expression:
  x = "Sathish"
  y = "Sathish"
  is_same_person = x is y  # True (strings are interned in Python)
  

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5. Order of Evaluation (Precedence)

• Python evaluates expressions based on operator precedence.
• Use parentheses () to override the default order.

result = 10 + 5 * 2  # 20 (multiplication is evaluated first)
result = (10 + 5) * 2  # 30 (parentheses override precedence)

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6. Best Practices

• Use parentheses to make complex expressions more readable.
• Break down complex expressions into smaller, meaningful parts.
• Use descriptive variable names to make expressions self-explanatory.

# Less readable
total = (x + y) * (a - b) / (c ** 2)

# More readable
sum_xy = x + y
diff_ab = a - b
square_c = c ** 2
total = (sum_xy * diff_ab) / square_c