Python Conditionals

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1. What are Conditionals?

• Conditionals are used to make decisions in a program based on certain conditions.
• They allow the program to execute specific blocks of code only if certain conditions are met.
• Python uses if, elif, and else keywords for conditionals.

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2. Types of Conditional Statements

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1. if Statement

• The if statement checks a condition. If the condition is True, the block of code under it is executed.
• Syntax:
  if condition:
      # Code to execute if condition is True
  

age = 20
if age >= 18:
    print("Raj is eligible to vote.")

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2. if-else Statement

• The else block is executed if the if condition is False.
• Syntax:
  if condition:
      # Code to execute if condition is True
  else:
      # Code to execute if condition is False
  

age = 16
if age >= 18:
    print("Ram is eligible to vote.")
else:
    print("Ram is not eligible to vote.")

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3. if-elif-else Statement

• The elif (else-if) statement allows you to check multiple conditions.
• The else block is executed if none of the if or elif conditions are True.
• Syntax:
  if condition1:
      # Code to execute if condition1 is True
  elif condition2:
      # Code to execute if condition2 is True
  else:
      # Code to execute if all conditions are False
  

marks = 85
if marks >= 90:
    print("Anand scored an A grade.")
elif marks >= 80:
    print("Anand scored a B grade.")
else:
    print("Anand scored a C grade.")

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4. Nested Conditionals

• You can nest if statements inside other if statements to check for more complex conditions.
• Syntax:
  if condition1:
      if condition2:
          # Code to execute if both conditions are True
  

age = 20
has_id = True
if age >= 18:
    if has_id:
        print("Bala is allowed to enter.")
    else:
        print("Bala needs an ID to enter.")
else:
    print("Bala is too young to enter.")

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3. Logical Operators in Conditionals

• Logical operators (and, or, not) are used to combine multiple conditions.
• and: Both conditions must be True.
• or: At least one condition must be True.
• not: Inverts the condition.

age = 20
has_license = True

if age >= 18 and has_license:
    print("Karthik can drive.")
else:
    print("Karthik cannot drive.")

if age < 18 or not has_license:
    print("Kumar cannot drive.")
else:
    print("Kumar can drive.")

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4. Ternary Operator (Conditional Expression)

• A shorthand way to write simple if-else statements in a single line.
• Syntax:
  value_if_true if condition else value_if_false
  

age = 20
status = "Eligible" if age >= 18 else "Not Eligible"
print(f"David is {status} to vote.")

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5. Additional Examples

• if Statement:
  name = "Siva"
  age = 22
  if age >= 18:
      print(f"{name} is eligible to vote.")
  
• if-else Statement:
  name = "Ramesh"
  marks = 75
  if marks >= 50:
      print(f"{name} has passed the exam.")
  else:
      print(f"{name} has failed the exam.")
  
• if-elif-else Statement:
  name = "Suresh"
  salary = 75000
  if salary >= 100000:
      print(f"{name} is in the high-income bracket.")
  elif salary >= 50000:
      print(f"{name} is in the middle-income bracket.")
  else:
      print(f"{name} is in the low-income bracket.")
  
• Nested Conditionals:
  name = "Sathish"
  age = 17
  has_permission = True
  if age >= 18:
      print(f"{name} can attend the event.")
  else:
      if has_permission:
          print(f"{name} can attend with parental permission.")
      else:
          print(f"{name} cannot attend the event.")
  
• Ternary Operator:
  name = "Sujatha"
  age = 16
  status = "Adult" if age >= 18 else "Minor"
  print(f"{name} is a {status}.")
  

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6. Best Practices

• Use meaningful variable names to make conditions clear.
• Avoid deeply nested conditionals to keep the code readable.
• Use parentheses to group complex conditions for clarity.
• Use comments to explain complex logic.

# Check if a person is eligible for a loan
age = 25
income = 60000
credit_score = 700

if (age >= 18) and (income >= 50000) and (credit_score >= 650):
    print("Eligible for a loan.")
else:
    print("Not eligible for a loan.")