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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.

Examples:

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., +, -, *, /).

Example:

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.

Example:

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.

Example:

# 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