Naming rules and conventions in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of variable naming with underscores

What is the output of this code snippet?

Python

my_var = 10
_myVar = 20
print(my_var + _myVar)

A 30

B 1020

C NameError

D SyntaxError

💡 Hint

Remember that variables starting with underscore are valid names.

Both variables are valid and hold integer values. Adding them results in 30.

❓ Predict Output

intermediate

Output with invalid variable name

What error does this code raise?

Python

2nd_var = 5
print(2nd_var)

A SyntaxError

B NameError

C TypeError

D 5

💡 Hint

Variable names cannot start with a number.

Variable names cannot begin with digits, so this causes a SyntaxError.

❓ Predict Output

advanced

Output of variable naming with reserved keywords

What error does this code produce?

Python

class = 10
print(class)

A TypeError

B SyntaxError

C 10

D NameError

💡 Hint

Reserved keywords cannot be used as variable names.

Using 'class' as a variable name is invalid and causes a SyntaxError.

❓ Predict Output

advanced

Output of variable naming with case sensitivity

What is the output of this code?

Python

Var = 5
var = 10
print(Var + var)

A 5

B 10

C 15

D NameError

💡 Hint

Python variable names are case sensitive.

Var and var are two different variables holding 5 and 10 respectively. Their sum is 15.

🧠 Conceptual

expert

Identify the valid variable names

Which of the following variable names are valid in Python? Select the one that is NOT valid.

A _myVar1

B myVar_2

C var3

D my-var

💡 Hint

Variable names cannot contain hyphens.

Variable names cannot have hyphens (-). Option D is invalid because of the hyphen.

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