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In this article, we explore how to execute code based on specific conditions using Python’s built-in conditional statements. Conditional statements are essential for controlling the flow of your program by executing certain blocks of code only when certain criteria are met.

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The if Statement

The simplest conditional statement in Python uses the if keyword. When the condition provided after if evaluates to True, the following indented block of code is executed: 
if condition:
    print("The condition is true!")
If the condition is False, Python skips the block and continues executing subsequent code.
Always remember to end your if statement line with a colon (:). Proper indentation is critical for Python to correctly interpret which statements belong to the block.

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Practical Example with User Input

Consider a scenario where we prompt the user to enter their age. We then use an if statement to determine if the user is 18 or older, outputting an appropriate message accordingly. For example, if a user enters the age 22, the program will confirm that the user is an adult: 
age = int(input("How old are you? "))
if age >= 18:
    print("You are an adult!")
When executed, the console interaction might look like this: 
How old are you? 22
You are an adult!

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The if-else Statement

Sometimes, you need to execute one block of code when a condition is true and a different block when it is false. Use the else keyword to provide an alternative: 
if condition:
    print("The condition is true!")
else:
    print("The condition is false!")
In this structure, if the initial condition is not met, the code under else will run.

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The if-elif-else Chain

For situations involving multiple conditions, Python’s elif keyword lets you check additional expressions sequentially. This structure allows you to have several branching paths: 
if False:
    print("The condition is true!")
elif True:
    print("Only the second condition is true!")
else:
    print("Both conditions are false!")
In this chain:
  • Python first evaluates the if condition.
  • If it evaluates to False, the program checks the elif condition.
  • If the elif condition is also False, the else block is executed.
Note that if an earlier condition is met, the rest of the conditions (elif or else) are ignored: 
if True:
    print("The condition is true!")
elif True:
    print("Only the second condition is true!")
else:
    print("Both conditions are false!")

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Nested Conditional Statements

You can nest conditional statements inside another to evaluate further conditions. For example, if you want to give a special message when a user’s age is exactly 18, use a nested if: 
if age >= 18:
    if age == 18:
        print("You are exactly 18 years old!")
    else:
        print("You are older than 18 years old!")
In this scenario:
  • The outer if checks if the user is an adult (18 or older).
  • If true, the inner if further checks whether the age is exactly 18.
  • If the inner condition is False, it indicates that the user is older than 18.
Using nested conditional statements helps create a more detailed decision-making process, allowing you to handle complex conditions efficiently.

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Summary of Conditional Statements

Statement TypeDescriptionExample Usage
ifExecutes code when a condition is Trueif condition: print("True condition")
if-elseProvides an alternative when the condition is Falseif condition: print("True") else: print("False")
if-elif-elseEvaluates multiple conditions sequentiallyif a: ... elif b: ... else: ...
Nested ifAllows deeper inspection by placing an if within an ifif age>=18: if age==18: print("Exactly 18") else: print("Above 18")

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Conclusion

This guide covered the fundamentals of conditional statements in Python. We examined the basic if statement, introduced the alternative else clause, explored chaining multiple conditions with elif, and demonstrated how to nest conditionals for refined control. These techniques form the backbone of decision-making in Python programming. Happy coding!

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