Variables and Basic Data Types

Variables: Your Labeled Boxes

Storing Data

In Python, variables are like labeled boxes. You give the box a name, and you put data inside it using the assignment operator (=).

This allows your program to remember and reuse information later.

Welcome to your first step in coding! Think of a variable as a labeled box. You give it a name, like 'user_age', and then you place a value inside using the equals sign. Now, whenever your program sees 'user_age', it knows you mean the number 25.

• Variables act as containers for data values.
• The '=' symbol assigns a value to a name.
• Variables make code reusable and readable.

The Art of Naming (PEP 8)

Naming Conventions

Python follows the PEP 8 style guide. For variables, we use snake_case.

• Do: user_score, total_price
• Don't: 1st_place (cannot start with a digit)
• Don't: UserScore (CamelCase is for other things)

Naming things correctly is a superpower. In Python, we use 'snake_case'—that means all lowercase letters with underscores between words. 'user_age' is perfect. But be careful! You can't start a name with a number, and remember that Python is case-sensitive, so 'Age' with a capital A is a totally different box than 'age' with a lowercase a.

• Use snake_case: all lowercase with underscores.
• Names cannot start with a digit.
• Python is case-sensitive: 'Age' and 'age' are different.

Understanding Data Types

The Four Core Types

Python automatically detects what kind of data you are storing:

• Integers (int): Whole numbers (10, -5).
• Floats (float): Decimals (3.14, 20.0).
• Strings (str): Text in quotes ("Hello").
• Booleans (bool): Logical True or False.

Python is smart enough to know what's in the box. Whole numbers are called Integers. If there's a decimal point, it's a Float. Text data, wrapped in quotes, is a String. And finally, Booleans are simple logical values: either True or False.

• Integers are for counting whole units.
• Floats are for precise measurements.
• Strings always require quotes.
• Booleans represent logic (on/off).

Math and Formatting

Calculations & f-strings

You can perform arithmetic directly with variables using +, -, *, and /.

To display results nicely, use an f-string: f"Text {variable}".

Variables aren't just for sitting in boxes; we can use them! You can multiply a 'price' variable by a 'quantity' variable to get a total. To tell the user the result, use an f-string. Just put an 'f' before your quotes and put the variable name inside curly braces. It's the cleanest way to format your output.

• Arithmetic operators: +, -, *, /.
• Division (/) always returns a float.
• f-strings (formatted strings) combine text and variables easily.

Code a User Message

Imagine you have two variables: name = "Alex" and score = 50. Write an f-string that would output: Alex has 50 points!

Now it's your turn. Try writing the f-string needed to print the message 'Alex has 50 points!' using the variables provided. Remember the 'f' and the curly braces!

• Start with f and quotes.
• Use curly braces {} for variables.
• Match the exact output format.

Avoiding Common Pitfalls

Watch Your Step!

• Type Mismatch: You can't add text and numbers directly ("Age: " + 25).
• Case Sensitivity: score is not Score.
• Type Checking: Use type(variable) if you're unsure.

Even pros make mistakes. A common one is trying to add a number to a string using a plus sign—Python will throw an error! Use f-strings instead. Also, always check your spelling and capitalization. If you ever get confused about what's inside a box, just use the 'type' function to ask Python directly.

• Never mix strings and numbers with a '+' sign.
• Verify variable types using the type() function.
• Double-check capitalization in variable names.