Creating custom modules in Python - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of importing and using a custom module function

Consider you have a file named mymath.py with this content:

def add(a, b):
    return a + b

What will be the output of this code?

import mymath
print(mymath.add(3, 4))

Python

import mymath
print(mymath.add(3, 4))

A 7

B 34

C TypeError

D NameError

💡 Hint

Remember that the function add returns the sum of two numbers.

The function add in mymath module adds two numbers. Calling mymath.add(3, 4) returns 7, which is printed.

❓ Predict Output

intermediate

Output when importing a module with a syntax error

Given a file mymodule.py with this content:

def greet(name):
    print(f"Hello, {name}!")

if True
    print("This line has a syntax error")

What happens when you run this code?

import mymodule
mymodule.greet("Alice")

Python

import mymodule
mymodule.greet("Alice")

A Hello, Alice!

B SyntaxError

C NameError

D IndentationError

💡 Hint

Check the if statement syntax in the module.

The module has a missing colon after 'if True', causing a SyntaxError when imported.

🔧 Debug

advanced

Why does this custom module import fail?

You have a file calculator.py with:

def multiply(x, y):
    return x * y

And this code in another file:

from Calculator import multiply
print(multiply(2, 3))

What is the cause of the error when running this code?

Python

from Calculator import multiply
print(multiply(2, 3))

A NameError because multiply is not defined

B TypeError because multiply is not a function

C SyntaxError because import statement is wrong

D ModuleNotFoundError because module name is case-sensitive

💡 Hint

Python module names are case-sensitive and must match the file name exactly.

The file is named 'calculator.py' but the import uses 'Calculator' with uppercase C. This causes ModuleNotFoundError.

📝 Syntax

advanced

Which import statement correctly imports all functions from a custom module?

You have a module tools.py with several functions.
Which option correctly imports all functions so you can call them directly without prefix?

A import tools.*

B from tools import all

C from tools import *

D import * from tools

💡 Hint

The syntax for importing all names from a module uses 'from module import *'.

Option C uses correct Python syntax to import all functions from tools so they can be called directly.

🚀 Application

expert

What is the output of this custom module usage with __name__ check?

Given a file greetings.py with:

def say_hello():
    print("Hello from greetings")

if __name__ == "__main__":
    say_hello()

And this code in another file:

import greetings
print("Imported greetings module")

What will be printed when running the second file?

Python

import greetings
print("Imported greetings module")

A Imported greetings module

B

Hello from greetings
Imported greetings module

C No output

D NameError

💡 Hint

Code inside 'if __name__ == "__main__"' runs only when the module is executed directly.

When greetings.py is imported, __name__ is 'greetings', so the say_hello() inside the if block does not run. Only the print in the second file runs.

Practice

1. What is the main purpose of creating a custom module in Python?

easy

A. To make the program run faster

B. To store data permanently

C. To create graphical user interfaces

D. To organize and reuse code easily

Solution

1. Step 1: Understand what a module is

   A module is a file containing Python code like functions or classes.

2. Step 2: Identify the purpose of custom modules

   Custom modules help organize code and allow reuse in different programs.

3. Final Answer:

   To organize and reuse code easily -> Option D

4. Quick Check:

   Custom modules = organize and reuse code [OK]

Hint: Modules group code for reuse and clarity [OK]

Common Mistakes:

• Thinking modules speed up code execution
• Confusing modules with data storage
• Assuming modules create user interfaces

2. Which of the following is the correct way to import a custom module named mymodule?

easy

A. import mymodule

B. include mymodule

C. using mymodule

D. load mymodule

Solution

1. Step 1: Recall Python import syntax

   Python uses the keyword import to bring in modules.

2. Step 2: Match correct syntax

   Only import mymodule is valid Python syntax for importing a module.

3. Final Answer:

   import mymodule -> Option A

4. Quick Check:

   Import module = import keyword [OK]

Hint: Use 'import' keyword to bring in modules [OK]

Common Mistakes:

• Using 'include' or 'load' which are not Python keywords
• Trying 'using' which is from other languages
• Misspelling 'import'

3. Given a file math_ops.py with this code:

def add(a, b):
    return a + b

What will be the output of this code?

import math_ops
print(math_ops.add(3, 4))

medium

A. 7

B. 34

C. TypeError

D. NameError

Solution

1. Step 1: Understand the function in math_ops.py

   The function add takes two numbers and returns their sum.

2. Step 2: Analyze the import and function call

   Importing math_ops allows calling math_ops.add(3, 4), which returns 3 + 4 = 7.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Imported functions run normally with correct arguments [OK]

Common Mistakes:

• Confusing string concatenation with addition
• Expecting errors due to import
• Forgetting to call function with parentheses

4. You have a module file named utils.py with a function greet(). Which of these import statements will cause an error?

medium

A. import utils

B. import utils.greet

C. from utils import greet

D. from utils import greet as hello

Solution

1. Step 1: Understand Python import rules

   You can import a module or specific functions from it, but not a function as a submodule.

2. Step 2: Check each option

   Options B, C, and D are valid. import utils.greet tries to import a function as a module, which causes ImportError.

3. Final Answer:

   import utils.greet -> Option B

4. Quick Check:

   Functions are imported, not as submodules [OK]

Hint: Import modules or functions, not functions as modules [OK]

Common Mistakes:

• Trying to import a function like a module
• Confusing 'from' and 'import' usage
• Using invalid aliases

5. You want to create a custom module text_utils.py with a function count_vowels(text) that returns the number of vowels in a string. Which code correctly defines this function?

hard

A. def count_vowels(text):
vowels = 'aeiou'
count = 0
for char in text:
if char in vowels:
count += 1
return count

B. def count_vowels(text):
vowels = ['a', 'e', 'i', 'o', 'u']
count = 0
for char in text:
if char in vowels:
count += 1
return count

C. def count_vowels(text):
vowels = 'aeiouAEIOU'
return sum(1 for char in text if char in vowels)

D. def count_vowels(text):
vowels = 'AEIOU'
count = 0
for char in text:
if char.lower() in vowels:
count += 1
return count

Solution

1. Step 1: Check vowel counting logic

   def count_vowels(text): vowels = 'aeiouAEIOU' return sum(1 for char in text if char in vowels) uses a string with both uppercase and lowercase vowels and counts characters in one line using sum and generator.

2. Step 2: Compare other options

   def count_vowels(text): vowels = ['a', 'e', 'i', 'o', 'u'] count = 0 for char in text: if char in vowels: count += 1 return count misses uppercase vowels, def count_vowels(text): vowels = 'aeiou' count = 0 for char in text: if char in vowels: count += 1 return count misses uppercase vowels, def count_vowels(text): vowels = 'AEIOU' count = 0 for char in text: if char.lower() in vowels: count += 1 return count incorrectly checks lowercase char in uppercase vowels string.

3. Final Answer:

   def count_vowels(text): vowels = 'aeiouAEIOU' return sum(1 for char in text if char in vowels) -> Option C

4. Quick Check:

   Count vowels with case check = def count_vowels(text): vowels = 'aeiouAEIOU' return sum(1 for char in text if char in vowels) [OK]

Hint: Use sum with generator and full vowel set for case [OK]

Common Mistakes:

• Ignoring uppercase vowels
• Checking lowercase char in uppercase vowels string
• Using list instead of string for vowels unnecessarily