Python If-else statements

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In every programming language, conditional statements form the backbone of decision-making. Python, known for its simplicity and readability, offers the if, elif, and else constructs to aid in this. This article will delve deep into Python’s if-else statements, exploring syntax, usage scenarios, best practices, and nuances.

1. Introduction to Conditional Statements

At its core, a conditional statement evaluates a condition (typically a boolean expression) and executes a specific block of code based on whether the condition is True or False. This allows for dynamic decision-making in a program.

For example, consider a simple real-life analogy: “If it rains, then I’ll take an umbrella. Otherwise, I won’t.” This logic can be directly translated into a program using conditional statements.

2. Python if Statement

The fundamental building block of Python’s conditional constructs is the if statement.


The if statement is the cornerstone of decision-making in programming. At its core, it allows a program to take different actions based on whether a specific condition is true or false. When the condition is true, the code block under the if statement gets executed. If the condition is false, that block of code is skipped.


The basic syntax for the if statement in Python is:

if condition:
    # block of code to be executed if the condition is True

Here’s what’s happening:

  1. if Keyword: This keyword initiates the conditional statement in Python.
  2. Condition: This is a Boolean expression (an expression that evaluates to either True or False).
  3. Colon (:): The colon signifies the start of the block of code that belongs to the if statement.
  4. Indented Code Block: In Python, indentation (whitespace) is crucial. It determines the scope of code blocks. Any code that you want to be executed when the condition is true should be indented under the if statement.


Let’s use an example to clarify:

age = 18

if age >= 18:
    print("You are eligible to vote.")

Here’s the step-by-step breakdown:

  1. We have a variable age set to 18.
  2. The if statement checks the condition age >= 18. This condition checks if the value of age is greater than or equal to 18.
  3. If the condition evaluates to True (which it does in this case since 18 is indeed greater than or equal to 18), the indented block of code underneath the if statement gets executed.
  4. As a result, You are eligible to vote. gets printed to the console.

If the age was, for instance, 16, the condition would evaluate to False, and nothing would get printed since the code block under the if statement would be skipped.

The Importance of Indentation

Indentation isn’t just for style in Python – it has syntactic significance. Let’s consider a modification to our previous example:

age = 18

if age >= 18:
    print("You are eligible to vote.")
print("This line executes regardless of the age value.")

In this example, the second print statement is not indented under the if statement, which means it’s not part of the if block. It will execute no matter what, irrespective of whether the condition in the if statement is true or false.

3. Python if-else Statement


While the if statement allows you to execute a block of code if a condition is True, there are often cases where you’d want to have an alternative action when the condition is False. This is where the else statement comes into play. Together, if and else provide a binary branching mechanism in your code, allowing for two distinct outcomes based on a condition.


The combined syntax for if and else is:

if condition:
    # block of code to be executed if the condition is True
    # block of code to be executed if the condition is False

Here’s a breakdown:

  1. if Keyword: As before, this keyword starts the conditional statement.
  2. Condition: A Boolean expression that will evaluate to either True or False.
  3. First Code Block: Indented under the if, this block will be executed if the condition is True.
  4. else Keyword: Follows the if block. It doesn’t have its own condition because it serves as a catch-all for when the if condition is False.
  5. Second Code Block: Indented under the else, this block will be executed if the if condition is False.


Let’s use a real-world inspired example for clarity:

temperature = 15

if temperature < 20:
    print("It's cold outside!")
    print("The weather is pleasant!")

Step-by-step breakdown:

  1. We have a variable temperature set to 15.
  2. The if statement checks the condition temperature < 20. This condition is asking, “Is the temperature less than 20 degrees?”
  3. If this condition is True (which it is, because 15 is less than 20), the code block beneath the if statement will execute. Thus, It's cold outside! will be printed.
  4. If the condition had been False (for instance, if the temperature was 25), then the code block beneath the else statement would execute, resulting in The weather is pleasant! being printed.

Importance of the Else Block

The else block serves as a default or fallback action. If none of the conditions in the preceding if (or elif, which we’ll discuss later) statements are True, the else block will always execute.

Typical Uses of if-else

The if-else construct is used in numerous scenarios:

Decision Making: As seen with the temperature example, we make a decision based on a condition.

Error Handling: Check for a potential error condition, and if it’s true, handle the error. Otherwise, proceed normally.

user_input = input("Enter a number: ")

if user_input.isdigit():
    print("Thank you for entering a number.")
    print("That's not a valid number!")

Input Validation: Ensure data fits certain criteria before processing it. If not, request new data or inform the user.

The if-else construct in Python enables bifurcation in the flow of your program. Based on a condition, it chooses between two blocks of code: one for when the condition is true, and another for when it’s false. This simple yet powerful tool forms the foundation of logic and decision-making in programming. As with the if statement, consistent and correct indentation is crucial in Python to ensure the correct scope and behavior of your code blocks.

4. Python elif Statement


While if checks a condition and else provides a default action when preceding conditions aren’t met, there’s often a need for checking multiple specific conditions sequentially. This is where elif, a contraction of “else if”, comes into the picture. The elif statement allows you to check multiple expressions for True and execute a block of code as soon as one of the conditions evaluates to True.


if condition1:
    # block of code if condition1 is True
elif condition2:
    # block of code if condition2 is True
elif condition3:
    # block of code if condition3 is True
    # block of code if none of the conditions are True

Here’s a breakdown:

  1. if Keyword: The initial condition check starts with the if.
  2. elif Keyword: Following the if, you can have any number of elif statements to check additional conditions. The program will evaluate these conditions in order and will execute the block of code for the first one that is True.
  3. else Keyword (Optional): After all the if and elif statements, you can have an else statement to catch any cases that haven’t been addressed by the previous conditions. Remember, this is optional; an if-elif structure doesn’t necessarily require an ending else.


Imagine a grading system:

score = 85

if score >= 90:
    grade = 'A'
elif score >= 80:
    grade = 'B'
elif score >= 70:
    grade = 'C'
elif score >= 60:
    grade = 'D'
    grade = 'F'

print(f"Your grade is: {grade}")

Step-by-step breakdown:

  1. We have a variable score set to 85.
  2. The if statement first checks if the score is 90 or above. If True, it assigns the grade ‘A’ and skips the rest of the checks.
  3. If the score isn’t 90 or above, the first elif checks if it’s 80 or above. If True, it assigns the grade ‘B’ and again skips the subsequent conditions.
  4. This process continues down the line of elif statements. If none of the conditions for if and elif are True, the else block will execute, assigning the grade ‘F’.
  5. In our example, the grade ‘B’ will be assigned to the variable grade, and “Your grade is: B” will be printed.

The Utility of elif

The power of elif lies in its ability to create multi-way branches. Instead of nesting multiple if statements (which can make code harder to read), elif provides a flattened structure for sequential checks.

Things to Remember

  • Only one block of code in the if-elif-else chain will be executed. As soon as one condition is found to be True, the corresponding block is run, and the entire chain is exited.
  • The order of conditions is crucial. The program evaluates conditions from top to bottom. If a previous condition has already been met, subsequent conditions (even if they’re true) won’t be checked. This is why, in our grading example, we start checking from the highest grade range downwards.
  • You can use any number of elif statements in your code. However, excessive use might indicate that there’s a more efficient way to structure your logic, possibly using data structures or loops.

The elif construct in Python allows for efficient, sequential condition checking, making it indispensable for complex decision-making. By chaining if, elif, and else, you can craft precise, multi-way branching structures in your programs. Remember to consider the order of conditions and ensure that your logic covers all potential scenarios to maintain the accuracy and reliability of your code.

5. Python Nested if Statements


In programming, there are often scenarios where you need to check a condition while another condition is already being checked – essentially, a condition within a condition. This leads us to the concept of “nested” if statements. In Python, just as you can nest loops, you can also nest if statements within other if, elif, and else blocks.

Basic Syntax

Here’s the fundamental structure of a nested if statement:

if condition1:
    # code
    if condition2:
        # code for when condition1 and condition2 are both True
    # more code for when condition1 is True

Here’s a breakdown:

  1. Outer if Condition: The initial condition (condition1) is checked first.
  2. Nested if Condition: If condition1 is True, the program enters the corresponding code block. Within this block, there’s another if statement checking a second condition (condition2).
  3. Code Execution: If both condition1 and condition2 are True, the code inside the nested if statement will execute.


Let’s use an illustrative example:

weather = "rainy"
temperature = 10

if weather == "rainy":
    print("It's raining!")
    if temperature < 15:
        print("It's also quite cold. You might need a jacket along with an umbrella.")

Step-by-step breakdown:

  1. We have two variables: weather set to “rainy” and temperature set to 10.
  2. The outer if statement checks if the value of weather is “rainy”. Since this is True, we enter the code block of this condition and print “It’s raining!”.
  3. Inside the outer if block, we have a nested if statement that checks if temperature is less than 15. Given that our temperature is 10, this condition is also True. As a result, “It’s also quite cold. You might need a jacket along with an umbrella.” gets printed.

Nested if-else

Just like singular if statements, nested if statements can also have accompanying else and elif clauses:

if condition1:
    if condition2:
        # code for when both condition1 and condition2 are True
        # code for when condition1 is True, but condition2 is False
    # code for when condition1 is False

Complex Nesting Example

Consider a scenario where we want to recommend an activity based on weather and time of day:

weather = "sunny"
time_of_day = "morning"

if weather == "sunny":
    if time_of_day == "morning":
        print("How about a morning jog?")
        print("Maybe play some outdoor sports in the afternoon?")
    if time_of_day == "morning":
        print("Stay in and read a book?")
        print("Watch a movie or play indoor games?")

This code provides different recommendations based on the combination of weather conditions and the time of day.

Points to Consider

  1. Readability: While nested if statements are powerful, they can make the code harder to read if overused. It’s a good idea to avoid very deep nesting as it can lead to confusion.
  2. Logical Flow: Ensure that the nesting and the conditions make logical sense. The order of evaluations and the structure should align with the intended flow of logic.
  3. Indentation: Proper indentation is crucial in Python, especially with nested structures. Each nested level should be indented consistently (typically by four spaces) to ensure that the code blocks are associated with the correct conditions.

Nested if statements in Python allow for intricate decision-making by testing multiple conditions in a structured manner. They provide the flexibility to handle complex scenarios and craft detailed logical flows in your programs. While they are an essential tool in a programmer’s arsenal, it’s crucial to use them judiciously and ensure that the resulting code remains clear and maintainable.


Python’s if-else statements provide a robust and intuitive mechanism for conditional logic and decision-making in your programs. By understanding their structure, nuances, and best practices, you can craft efficient and clear code. Whether you’re writing a simple script or a complex application, mastering if-else is essential for any Python programmer.

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