Naming rules and conventions in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What characters can you use to start a variable name in Python?

A variable name must start with a letter (a-z, A-Z) or an underscore (_). It cannot start with a number or special character.

beginner

Is the variable name my-variable valid in Python? Why or why not?

No, because the hyphen (-) is not allowed in variable names. Use underscores (_) instead, like my_variable.

beginner

What is the naming convention for constants in Python?

Constants are usually written in all uppercase letters with underscores separating words, like MAX_SPEED.

beginner

How should you name a function in Python according to conventions?

Function names should be lowercase with words separated by underscores, like calculate_total.

beginner

Why should you avoid using Python reserved keywords as variable names?

Reserved keywords have special meaning in Python and using them as variable names will cause errors or unexpected behavior.

Which of these is a valid Python variable name?

A user-name

B user_name

C 2ndUser

D user name

Variable names cannot start with a number, contain hyphens, or spaces. Only 'user_name' is valid.

What is the correct way to name a constant in Python?

A MAX_SPEED

B maxSpeed

C max_speed

D MaxSpeed

Constants are written in all uppercase letters with underscores separating words.

Which of these is NOT allowed as a variable name in Python?

A class

B _temp

C total1

D value_2

'class' is a reserved keyword in Python and cannot be used as a variable name.

How should function names be written in Python?

A CalculateTotal

B calculate-total

C calculate_total

D calculateTotal

Function names use lowercase letters with underscores between words.

Which character is NOT allowed in Python variable names?

A a

B 9

C _

D -

Hyphens (-) are not allowed in variable names.

Explain the basic rules for naming variables in Python.

Think about what characters are allowed and what is not.

Describe the common naming conventions for constants and functions in Python.

Consider how uppercase and lowercase letters are used.

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