Python If Conditions

Learn how to write conditional statements to add decision-making logic to your Python code.

8 minutesVideo LessonPDF notes

🎯 Free Guest Mode: You are learning for free. Sign in to save your completion progress and quiz answers.

Ready to continue?

Mark this lesson as complete when you're ready to proceed.

Key moments

If Statement Introduction — If statements enable basic decision making by executing code only if a condition is true.
Basic If Syntax — The basic syntax requires 'if', a condition, a colon, and an indented code block.
Adding Else — The else statement provides a default course of action if the initial if condition is false.
Using Elif — The elif (else if) statement allows checking multiple conditions sequentially before the final else.
Order of Checks — The order of if and elif statements is critical because Python executes the first true condition and then exits the structure.
Comparison Operator — Use double equals (==) for comparison checks, distinguishing it from the single equals (=) assignment operator.
Booleans as Conditions — Boolean variables can be used directly in an if statement because they already evaluate to True or False.

PDF notes

Bottom line: You will learn to control program flow by executing code blocks only when specific conditions are met. This decision-making structure, using if, elif, and else, is fundamental for creating dynamic and responsive data analysis scripts.

This lesson on Python If Conditions is hands-on and example-driven. You will learn to control program flow by executing code blocks only when specific conditions are met. This decision-making structure, using if, elif, and else, is fundamental for creating dynamic and responsive data analysis scripts.

What You'll Be Able To Do

Implement conditional logic using if, elif, and else statements.
Differentiate between the assignment operator (=) and the comparison operator (==).
Structure complex decision trees where the order of conditions is critical.
Use Boolean variables directly within if statements to check state.
Validate user input by checking for specific values or empty strings.

Detailed Concept Walkthrough

1. Basic If/Else Structure

If statements allow code execution to depend on whether a condition evaluates to True. The else block provides a guaranteed default action if the initial condition is False.

Syntax Rule: The condition must be followed by a colon (:) and the subsequent code block must be indented (usually 4 spaces) to define its scope.
Mechanism: Python evaluates the expression after 'if'. If the result is True, the indented block runs; if False, the block is skipped and the program moves to the 'else' block, if present.
Execution Flow: Only one block runs: either the 'if' block (if true) or the 'else' block (if false).
Best Practice: Use the 'else' statement as a last resort or catch-all when no other condition has been met.

age = 13
if age >= 18:
    print("You are now signed up")
else:
    print("You must be 18 plus to sign up")

Key Takeaway: Indentation is mandatory and defines which lines of code belong to the conditional block.

2. Multi-way Decision Trees (Elif)

The 'elif' (else if) statement allows you to check multiple conditions sequentially, creating a chain of checks before falling back to the final 'else' block.

Execution Flow: Python checks conditions top-to-bottom. As soon as one condition evaluates to True, its corresponding block executes, and the entire if/elif/else structure is exited.
Mechanism: An 'elif' condition is only evaluated if the preceding 'if' and any previous 'elif' conditions were False.
Best Practice: The order of 'if' and 'elif' statements is critical; place the most specific or restrictive conditions first to ensure they are checked before more general, overlapping conditions.

age = 111
if age >= 100:
    print("Too old")
elif age >= 18:
    print("Signed up")
else:
    print("Too young")

Key Takeaway: Structure your conditional chain from the most specific check to the most general check.

3. Comparison Operators and Booleans

Conditional statements rely on comparison operators (like ==) to produce a Boolean result (True or False). Boolean variables can be used directly as conditions.

Syntax Rule: Use double equals (==) for checking equality; single equals (=) is the assignment operator and will cause errors if used for comparison.
Mechanism: Comparison operators return a Boolean value, which is exactly what the 'if' statement requires to decide execution flow.
Under the Hood: When an 'if' statement encounters a Boolean variable (e.g., 'if for_sale:'), it implicitly checks if the variable's value is True.
Best Practice: Avoid confusing assignment (=) with comparison (==) when validating user input or checking variable states.

for_sale = True
response = 'y'

if for_sale:
    print("Item is for sale")

if response == 'y':
    print("Confirmed")

Key Takeaway: A condition is any expression that evaluates to True or False.

Topics Covered in Python If Conditions

If Statement Introduction (0:00 - 0:30) — If statements enable basic decision making by executing code only if a condition is true.
Basic If Syntax (0:30 - 1:15) — The basic syntax requires 'if', a condition, a colon, and an indented code block.
Adding Else (1:15 - 2:00) — The else statement provides a default course of action if the initial if condition is false.
Using Elif (2:00 - 3:00) — The elif (else if) statement allows checking multiple conditions sequentially before the final else.
Order of Checks (3:00 - 4:30) — The order of if and elif statements is critical because Python executes the first true condition and then exits the structure.
Comparison Operator (4:30 - 5:30) — Use double equals (==) for comparison checks, distinguishing it from the single equals (=) assignment operator.
Booleans as Conditions (6:30 - 7:30) — Boolean variables can be used directly in an if statement because they already evaluate to True or False.

Python Cheat Sheet

if condition: — Starts a conditional block
```
if age >= 18:
```
elif condition: — Checks another condition if previous checks failed
```
elif age < 0:
```
else: — Executes if all preceding checks failed
```
else:
    print("Default")
```
== — Checks if two values are equal
```
if response == 'y':
```
= — Assigns a value to a variable
```
age = 21
```
Boolean Variable — Used directly as a condition
```
for_sale = True
if for_sale:
```

Comparison Table

Operator	Function	Result Type
=	Assignment	Variable Value
==	Comparison (Equality)	Boolean (True/False)
>=	Comparison (Greater/Equal)	Boolean (True/False)

Common Pitfalls

Mistake: Using single = for equality checks. Avoid: Use double == for comparison operations.
Mistake: Forgetting the colon after if, elif, or else. Avoid: Always terminate the conditional line with a colon (:).
Mistake: Incorrectly ordering overlapping elif conditions. Avoid: Place the most specific conditions first (e.g., age > 100 before age > 18).
Mistake: Missing indentation in the code block. Avoid: Ensure all code within the block is consistently indented (usually 4 spaces).

FAQs

Why does the order of if/elif matter? Python stops checking as soon as it finds the first True condition. If a general condition is placed first, it might execute prematurely, skipping more specific checks.
Can I use a Boolean variable directly in an if statement? Yes. Since the if statement requires a True or False result, a Boolean variable can be used directly without explicit comparison.
What happens if I don't include an else block? If the condition is False, the program simply skips the if block and continues executing the code immediately following the conditional structure.

Common pitfalls

Mistake: Using single = for equality checks. Avoid: Use double == for comparison operations.
Mistake: Forgetting the colon after if, elif, or else. Avoid: Always terminate the conditional line with a colon (:).
Mistake: Incorrectly ordering overlapping elif conditions. Avoid: Place the most specific conditions first (e.g., age > 100 before age > 18).
Mistake: Missing indentation in the code block. Avoid: Ensure all code within the block is consistently indented (usually 4 spaces).

hey everybody in this topic I'm going to explain if statements and if statement is used to do some code only if some condition we set is true else we could do something else it's a basic form of decision making if it's true we do something if it's not true we don't do it let's ask a user for their age age equals input enter your age I will type cast the input as an integer depending on what the user's age is we can do one of a few things let's pretend that the user would like to sign up for a credit card but in order to do so their age needs to be greater than or equal to 18. well we can check that to use an if statement type if then some condition what would we like to check let's check to see if the user's age is greater than or equal to 18 then add a colon then hit enter any code underneath the if statement should be indented make sure to pay attention to that because that's easy to miss if the user's age is greater than or equal to 18 let's print you are now signed up if I were to run this code I'll type in my age I'll type 21 hit enter this statement is true therefore we will execute any code found within the if statement you are now signed up what if this condition was not true let's say my age is 13. well nothing happens if the condition we check is instead false we skip over this code if you need to take a different course of action you could add an else statement if this is true do this else we can do something else let's print a different message you must be 18 plus to sign up I'll type in my age again I'll say that I'm 13. hit enter you must be 18 plus to sign up that's basically an if statement do some code only if some condition is true else you could do something else entirely it's a basic form of decision making the else statement is kind of like a last resort we can check more than one condition before reaching the else statement we can add an else if statement which we just shortened to e-l-i-f meaning else if else if let's check if age is less than zero then we'll print a different message you haven't been born yet now if I run this code I'll say that my age is negative one this condition is false we skip this code this condition is true therefore we will execute this code and we skip the else statement you haven't been born yet let's add another elsif statement you can add as many elsif statements as you want let's check to see if somebody's age is greater than or equal to 100 we'll print a different message let's print you are too old to sign up if I were to say my age is 111 years old well it states you are now signed up the reason that we didn't reach this part of our elsif statement that's because this condition is still technically true you do need to pay attention to your order of if and else if statements if I want to be sure that nobody over 100 is signing up I should probably move this to the beginning if age is greater than or equal to 100 then else if age is greater than or equal to 18 we'll do something else and to your age I am 111 years old you are too old to sign up so those are if statements if some condition is true do something else if you can check something else if no above conditions are true you could do something else entirely it's kind of like the default here's another example we'll ask a user if they would like some food response equals input would you like food we'll have the user type in y for yes or n for no if our response now to check to see if two values are equal you would use double equals if the response is equal to y then we will print have some food the doubles equal sign is the comparison operator it will check to see if two values are equal you don't want one equals because that's the assignment operator python in this case thinks we're attempting to assign the character y to response so for comparisons use double equals else we can print no food for you so would you like food I'll type why have some food let's try it again I'll type no and for no no food for you here's a third example we'll have a user type in their name name equals input enter your name if our name is equal to an empty string that means they didn't type in anything so let's yell at the user you did not type in your name else we will print using an F string hello whatever the name is enter your name I'm just going to hit enter you did not type in your name let's run this again I'll type in my name and we have executed the else statement this time hello bro so one important thing that you should know is the use of boolean's width if statements suppose we have some Boolean variable named for sale I'll set this to be true now using an if statement you can just use the Boolean variable in place of a condition because a condition would evaluate to be true or false we could just say if for sale if that's true then let's print this item is for sale else we will print this item is not for sale for sale is set to be true this item is for sale if this variable were false well then the item is not for sale let's try a different variable how about online if online the user is online else the user is offline so the user is offline I'll change the Boolean to true the user is online so with if statements you can either write a condition or you could use a Boolean all right everybody so those are if statements do some code only if some condition is true else you can do something else it's a basic form of decision making and those are if statements in Python

Frequently asked questions

Why does the order of if/elif matter?

Python stops checking as soon as it finds the first True condition. If a general condition is placed first, it might execute prematurely, skipping more specific checks.

Can I use a Boolean variable directly in an if statement?

Yes. Since the if statement requires a True or False result, a Boolean variable can be used directly without explicit comparison.

What happens if I don't include an else block?

If the condition is False, the program simply skips the if block and continues executing the code immediately following the conditional structure.

How was this lesson?

Your feedback helps us refine explanations and catch bugs.