Default arguments in Python - Mini Project: Build & Apply

Using Default Arguments in Python Functions

📖 Scenario: Imagine you are creating a simple greeting system for a website. Sometimes users provide their name, and sometimes they don't. You want to write a function that can greet users by name if given, or greet them with a friendly default message if no name is provided.

🎯 Goal: Build a Python function called greet that uses a default argument to greet a user by name if given, or greet with a default message if no name is provided.

📋 What You'll Learn

Create a function named greet with one parameter called name that has a default value of "Guest".

Inside the function, return a greeting string that says "Hello, {name}! Welcome!" using an f-string.

Call the function greet twice: once without any argument, and once with the argument "Alice".

Print the results of both function calls.

💡 Why This Matters

🌍 Real World

Default arguments help make functions flexible and easier to use in real-world programs where some information might be optional.

💼 Career

Understanding default arguments is important for writing clean, reusable code in software development jobs.

1

Create the greet function with a default argument

Write a function called greet that has one parameter named name with a default value of "Guest".

Python

# Your code here

Hint

Use the syntax def function_name(parameter=default_value): to create a function with a default argument.

2

Return a greeting message using the name parameter

Inside the greet function, write a return statement that returns the string "Hello, {name}! Welcome!" using an f-string.

Python

def greet(name="Guest"):
    # Your code here

Hint

Use return f"Hello, {name}! Welcome!" to create a formatted string that includes the name variable.

3

Call the greet function with and without an argument

Call the function greet twice: once without any argument and once with the argument "Alice". Store the results in variables greeting1 and greeting2 respectively.

Python

def greet(name="Guest"):
    return f"Hello, {name}! Welcome!"

# Your code here

Hint

Call greet() without arguments and greet("Alice") with the argument, then save the results.

4

Print the greetings

Print the variables greeting1 and greeting2 to display the greeting messages.

Python

def greet(name="Guest"):
    return f"Hello, {name}! Welcome!"

greeting1 = greet()
greeting2 = greet("Alice")

# Your code here

Hint

Use print(greeting1) and print(greeting2) to show the greetings.

Practice

1. What is the main purpose of default arguments in Python functions?

easy

A. To create variables inside the function

B. To provide preset values for parameters if no argument is given

C. To make functions run faster

D. To force the user to always provide all arguments

Solution

1. Step 1: Understand default arguments

   Default arguments allow a function to have parameters with preset values if the caller does not provide them.

2. Step 2: Identify the purpose

   This makes the function easier to call without needing all arguments every time.

3. Final Answer:

   To provide preset values for parameters if no argument is given -> Option B

4. Quick Check:

   Default arguments = preset values [OK]

Hint: Default arguments fill in missing inputs automatically [OK]

Common Mistakes:

• Thinking default arguments speed up code
• Believing default arguments force all inputs
• Confusing default arguments with variable creation

2. Which of the following function definitions uses default arguments correctly?

easy

A. def greet(name='Friend', age):

B. def greet(name=, age=30):

C. def greet(name, age=30):

D. def greet(name, age=):

Solution

1. Step 1: Check default argument placement

   Parameters with default values must come after parameters without defaults.

2. Step 2: Analyze each option

   def greet(name='Friend', age): places a default before a non-default parameter, which is invalid syntax. Options C and D have syntax errors. def greet(name, age=30): correctly places the default argument after a required parameter.

3. Final Answer:

   def greet(name, age=30): -> Option C

4. Quick Check:

   Defaults after required params = correct syntax [OK]

Hint: Put default parameters after required ones [OK]

Common Mistakes:

• Placing default arguments before required ones
• Leaving default values empty
• Using invalid syntax for defaults

3. What is the output of this code?

def multiply(a, b=2):
    return a * b

print(multiply(4))
print(multiply(4, 3))

medium

A. Error

B. 6 and 12

C. 8 and 6

D. 8 and 12

Solution

1. Step 1: Understand default argument usage

   When multiply(4) is called, b uses its default value 2, so 4 * 2 = 8.

2. Step 2: Evaluate second call

   When multiply(4, 3) is called, b is 3, so 4 * 3 = 12.

3. Final Answer:

   8 and 12 -> Option D

4. Quick Check:

   Default used first call, explicit second call = 8 and 12 [OK]

Hint: Default used if argument missing, else explicit value [OK]

Common Mistakes:

• Assuming default is ignored when argument is given
• Confusing order of arguments
• Expecting error when default is used

4. Find the error in this function definition:

def add_numbers(x=5, y):
    return x + y

medium

A. Default argument before non-default argument causes SyntaxError

B. Missing return statement

C. Function name is invalid

D. No error, code runs fine

Solution

1. Step 1: Check parameter order

   Parameters with default values must come after parameters without defaults in Python.

2. Step 2: Identify error

   Here, x has a default but y does not, so this causes a SyntaxError.

3. Final Answer:

   Default argument before non-default argument causes SyntaxError -> Option A

4. Quick Check:

   Default before required param = SyntaxError [OK]

Hint: Non-default params must come before default ones [OK]

Common Mistakes:

• Ignoring parameter order rules
• Thinking missing return causes error here
• Assuming function name is invalid

5. You want a function that greets a user with their name and an optional greeting word (default is 'Hello'). Which function definition is correct and prints "Hi, Alice!" when called as greet('Alice', 'Hi') and "Hello, Bob!" when called as greet('Bob')?

hard

A. def greet(name, greeting='Hello'):
print(f"{greeting}, {name}!")

B. def greet(greeting='Hello', name):
print(f"{greeting}, {name}!")

C. def greet(name, greeting):
print(f"{greeting}, {name}!")

D. def greet(name='User', greeting='Hello'):
print(f"{name}, {greeting}!")

Solution

1. Step 1: Check parameter order and defaults

   Parameters with defaults must come after those without. def greet(name, greeting='Hello'): print(f"{greeting}, {name}!") has name first (no default), greeting second (default 'Hello').

2. Step 2: Verify behavior

   Calling greet('Alice', 'Hi') prints "Hi, Alice!". Calling greet('Bob') uses default greeting "Hello" and prints "Hello, Bob!".

3. Final Answer:

   def greet(name, greeting='Hello'): print(f"{greeting}, {name}!") -> Option A

4. Quick Check:

   Defaults after required params, works as expected [OK]

Hint: Put required params first, defaults after [OK]

Common Mistakes:

• Placing default param before required param
• Not providing default for optional greeting
• Using default for name causing unexpected calls