Naming rules and conventions in Python - Mini Project: Build & Apply

Naming rules and conventions

📖 Scenario: You are helping a friend organize their small library of books using Python. To keep things clear and easy to understand, you will use proper naming rules and conventions for variables.

🎯 Goal: Create variables with correct names following Python naming rules and conventions, then print them to see the results.

📋 What You'll Learn

Create variables with valid Python names

Use lowercase letters and underscores for variable names

Avoid starting variable names with numbers or special characters

Print the variables to show their values

💡 Why This Matters

🌍 Real World

Using clear and correct variable names helps programmers and others understand code easily, just like labeling books in a library.

💼 Career

Good naming conventions are essential for writing clean, maintainable code in any programming job.

1

Create variables with valid names

Create three variables with these exact names and values: book_title with value "Python Basics", author_name with value "Anna Smith", and year_published with value 2023.

Python

# Create variables book_title, author_name, and year_published with given values
# Your code here

Hint

Use only letters, numbers, and underscores. Variable names cannot start with a number.

2

Add a variable with a valid name for book price

Create a variable called book_price and set it to the value 29.99.

Python

book_title = "Python Basics"
author_name = "Anna Smith"
year_published = 2023
# Create variable book_price with value 29.99
# Your code here

Hint

Remember to use lowercase letters and underscores for variable names.

3

Use a for loop with a proper variable name

Use a for loop with the variable info to iterate over the list [book_title, author_name, year_published, book_price] and print each info item.

Python

book_title = "Python Basics"
author_name = "Anna Smith"
year_published = 2023
book_price = 29.99
# Use for loop with variable info to print each item in the list
# Your code here

Hint

Use the variable name info exactly in the for loop.

4

Print a summary using f-string with proper variable names

Print a summary sentence using an f-string: "The book 'Python Basics' by Anna Smith was published in 2023 and costs $29.99." Use the variables book_title, author_name, year_published, and book_price inside the f-string.

Python

book_title = "Python Basics"
author_name = "Anna Smith"
year_published = 2023
book_price = 29.99
for info in [book_title, author_name, year_published, book_price]:
    print(info)
# Print the summary sentence using an f-string
# Your code here

Hint

Use print(f"...") with the variable names inside curly braces.

Practice

1. Which of the following is a valid variable name in Python?

easy

A. my-variable

B. 2ndVariable

C. my_variable

D. my variable

Solution

1. Step 1: Check the first character of each name

   Python variable names must start with a letter or underscore, not a number or special character.

2. Step 2: Identify invalid characters

   Names cannot contain spaces or hyphens. Only letters, digits, and underscores are allowed.

3. Final Answer:

   my_variable -> Option C

4. Quick Check:

   Valid variable name = my_variable [OK]

Hint: Variable names start with letter/underscore, no spaces or hyphens [OK]

Common Mistakes:

• Starting variable name with a number
• Using hyphens instead of underscores
• Including spaces in variable names

2. Which of these is the correct way to name a class in Python?

easy

A. MyClass

B. my_class

C. myclass

D. myClass

Solution

1. Step 1: Recall class naming convention

   Class names in Python use CapitalizedWords style (PascalCase), starting with uppercase letters.

2. Step 2: Compare options to convention

   Only 'MyClass' follows CapitalizedWords style correctly.

3. Final Answer:

   MyClass -> Option A

4. Quick Check:

   Class name style = CapitalizedWords [OK]

Hint: Class names use CapitalizedWords (PascalCase) [OK]

Common Mistakes:

• Using lowercase or underscores for class names
• Starting class names with lowercase letters
• Mixing camelCase with underscores

3. What will be the output of this code?

_count = 5
Count = 10
print(_count + Count)

medium

A. NameError

B. 15

C. SyntaxError

D. 510

Solution

1. Step 1: Understand variable names and case sensitivity

   Python variable names are case-sensitive, so '_count' and 'Count' are different variables.

2. Step 2: Calculate the sum of the two variables

   _count = 5 and Count = 10, so 5 + 10 = 15.

3. Final Answer:

   15 -> Option B

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Variable names are case-sensitive; add values accordingly [OK]

Common Mistakes:

• Ignoring case sensitivity and treating variables as same
• Expecting concatenation instead of addition
• Assuming syntax or name errors

4. Find the error in this variable name:

user-name = 'Alice'

medium

A. Variable names cannot contain hyphens

B. Variable names cannot start with a letter

C. Variable names cannot contain underscores

D. Variable names cannot be lowercase

Solution

1. Step 1: Identify invalid characters in variable names

   Hyphens are not allowed in Python variable names because they are interpreted as minus signs.

2. Step 2: Confirm other options are incorrect

   Variable names can start with letters, contain underscores, and be lowercase.

3. Final Answer:

   Variable names cannot contain hyphens -> Option A

4. Quick Check:

   Hyphens not allowed in names [OK]

Hint: No hyphens in variable names; use underscores instead [OK]

Common Mistakes:

• Using hyphens instead of underscores
• Thinking variable names can't start with letters
• Confusing underscores with invalid characters

5. You want to create a dictionary where keys are variable names and values are their types. Which naming style is best for the keys?

variables = { 'UserName': str, 'user_age': int, '2ndUser': str }

Which keys follow Python naming rules and conventions?

hard

A. 'user_age' only

B. All keys are valid

C. 'UserName' only

D. 'UserName' and 'user_age' only

Solution

1. Step 1: Check each key for naming rules

   'UserName' starts with a letter and uses CapitalizedWords (good for class names). 'user_age' uses lowercase with underscore (good for variables). '2ndUser' starts with a number, which is invalid.

2. Step 2: Identify keys following naming conventions

   'UserName' and 'user_age' follow naming rules; '2ndUser' does not.

3. Final Answer:

   'UserName' and 'user_age' only -> Option D

4. Quick Check:

   Keys must start with letter; numbers not allowed [OK]

Hint: Keys must start with letter; numbers not allowed [OK]

Common Mistakes:

• Allowing keys starting with numbers
• Ignoring naming conventions for readability
• Assuming all strings are valid variable names