Why Is My Python if Statement Running Too Many Times?

You're starting to build programs that can make decisions. It’s a huge step forward! You decide to write a simple program to assign a letter grade based on a score. The logic seems simple:

• If the score is over 90, the grade is 'A'.

• If the score is over 80, the grade is 'B'.

• And so on...

You translate this into Python using a series of if statements, and it looks perfectly correct:

Python

score = 95

if score >= 90:
    print("Grade is A")

if score >= 80:
    print("Grade is B")

if score >= 70:
    print("Grade is C")

You run the code, expecting to see just "Grade is A". Instead, you get this confusing output:

Grade is A
Grade is B
Grade is C

Why did all three if statements run? It feels like Python is ignoring your logic. This isn't a bug; it's a very common misunderstanding of how Python makes decisions. Let's clear it up and fix it.

The Problem: Asking Separate Questions vs. Making One Choice

The reason your code runs all three print statements is that you are using a series of separate if statements. You can think of this as asking a series of completely independent, unrelated questions.

Here's how Python sees your code:

1. Question 1: "Is the score (95) greater than or equal to 90?" The answer is True. Okay, I will print "Grade is A".

2. Forgetting Question 1: Python now completely forgets about the first question. It moves on to the next line as if it's a brand new problem.

3. Question 2: "Is the score (95) greater than or equal to 80?" The answer is True. Okay, I will print "Grade is B".

4. Forgetting Question 2: Again, it forgets the past and moves on.

5. Question 3: "Is the score (95) greater than or equal to 70?" The answer is True. Okay, I will print "Grade is C".

Using multiple ifs in a row is perfect when you need to check for multiple different things that could all be true at the same time. But for a grading system, you only want one answer.

The Solution: Using elif to Chain Your Logic

To tell Python you want it to choose only one option from a list of possibilities, you need to create a "logical chain." You do this with if, elif (short for "else if"), and else.

Here’s how the logic works in an if/elif/else chain:

• Python checks the first if.

• If it's True, it runs that code block and skips the rest of the entire chain. It doesn't even look at the elif or else conditions.

• If it's False, and only if it's false, it moves down to the first elif and checks that condition.

• It continues down the chain until it finds a condition that is True, runs that code, and then exits the chain.

Let's rewrite our grading program the correct way:

Python

score = 95

if score >= 90:
    print("Grade is A")
elif score >= 80:
    print("Grade is B")
elif score >= 70:
    print("Grade is C")
else:
    print("Grade is F")

Now, when you run this with score = 95:

1. Question 1: "Is the score (95) greater than or equal to 90?" The answer is True.

2. Action: Python prints "Grade is A".

3. Exit: Because the first condition was met, Python skips the entire rest of the elif and else blocks.

The output is now correct: Grade is A.

Don't Forget else: The Safety Net

The else statement at the end is an optional but very useful "catch-all." It doesn't have a condition. Its code runs if, and only if, all the preceding if and elif conditions were False. It’s your safety net for any case you didn't explicitly check for.

Frequently Asked Questions (FAQs)

1. Can I have an elif or else without a starting if?

No. An if/elif/else chain must always begin with exactly one if statement.

2. How many elif statements can I use in a chain?

As many as you need! You can have zero, one, or dozens of elif statements between your if and your optional else.

3. Do I always need an else?

No, else is completely optional. You can have an if block by itself or an if/elif chain without a final else.

4. What are the colons (:) and indentation for?

This is fundamental to Python's syntax. The colon (:) at the end of a line like if score >= 90: signifies the beginning of a code block. All the code that should be executed if that condition is true must be indented underneath it. This indentation is not optional; it's how Python groups your code.

Conclusion: You Can Now Control the Flow

This is a huge step in your programming journey. You haven't just learned a piece of syntax; you've learned how to control the logical flow of your application.

Here’s the simple takeaway:

• Use a series of if statements for separate, independent checks where multiple conditions could be true.

• Use an if/elif/else chain when you need to select just one choice from a list of mutually exclusive options.

Understanding this distinction will save you from countless bugs and make your code behave exactly as you intend. What's the first decision-making program you plan to build?