Variable-length keyword arguments (**kwargs) in Python - Mini Project: Build & Apply

Using Variable-Length Keyword Arguments (**kwargs) in Python

📖 Scenario: You are creating a simple program to store information about a car. Different cars have different features, so you want a flexible way to add any number of details about each car.

🎯 Goal: Build a Python function that accepts any number of named details about a car using **kwargs and then prints those details.

📋 What You'll Learn

Create a function called car_info that accepts variable-length keyword arguments using **kwargs.

Inside the function, use a for loop with variables key and value to iterate over kwargs.items().

Print each key and value pair in the format: key: value.

Call the function with at least three named arguments representing car details.

💡 Why This Matters

🌍 Real World

Many programs need to handle flexible data inputs, like user profiles or product details, where the exact information can vary.

💼 Career

Understanding <code>**kwargs</code> is important for writing adaptable Python functions used in web development, data processing, and automation tasks.

1

Define the car_info function with **kwargs

Write a function called car_info that accepts variable-length keyword arguments using **kwargs. Inside the function, write a pass statement for now.

Python

def car_info(**kwargs):
    # Your code here
    pass

Hint

Use def car_info(**kwargs): to define the function and write pass inside to keep it empty for now.

2

Add a for loop to iterate over kwargs.items()

Inside the car_info function, add a for loop with variables key and value to iterate over kwargs.items(). For now, just write pass inside the loop.

Python

def car_info(**kwargs):
    for key, value in kwargs.items():
        # Your code here
        pass

Hint

Use for key, value in kwargs.items(): to loop through all keyword arguments.

3

Print each key and value inside the loop

Replace the pass inside the for loop with a print statement that shows the key and value in the format: key: value using an f-string.

Python

def car_info(**kwargs):
    for key, value in kwargs.items():
        # Your code here
        print(f"{key}: {value}")

Hint

Use print(f"{key}: {value}") to display each detail clearly.

4

Call car_info with three named arguments and print the output

Call the car_info function with these exact named arguments: make='Toyota', model='Corolla', and year=2020. This will print the car details.

Python

def car_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

# Your code here
car_info(make='Toyota', model='Corolla', year=2020)

Hint

Call car_info(make='Toyota', model='Corolla', year=2020) exactly to see the details printed.

Practice

1. What does **kwargs allow you to do in a Python function?

easy

A. Pass a variable number of keyword arguments as a dictionary

B. Pass a variable number of positional arguments as a tuple

C. Return multiple values from a function

D. Define a function without any parameters

Solution

1. Step 1: Understand **kwargs usage

   **kwargs collects extra keyword arguments into a dictionary inside the function.

2. Step 2: Compare with other options

   Pass a variable number of positional arguments as a tuple describes *args, not **kwargs. Options A and C are unrelated to **kwargs.

3. Final Answer:

   Pass a variable number of keyword arguments as a dictionary -> Option A

4. Quick Check:

   **kwargs = keyword args dict [OK]

Hint: Remember: **kwargs collects named arguments as a dict [OK]

Common Mistakes:

• Confusing *args with **kwargs
• Thinking **kwargs collects positional arguments
• Believing **kwargs returns multiple values

2. Which of the following is the correct way to define a function that accepts variable keyword arguments?

easy

A. def func(*kwargs):

B. def func(**kwargs):

C. def func(**kwargs, *args):

D. def func(kwargs**):

Solution

1. Step 1: Recall correct syntax for keyword arguments

   The correct syntax to accept variable keyword arguments is **kwargs.

2. Step 2: Check each option

   def func(*kwargs): uses single star which is for positional args. def func(**kwargs, *args): is invalid syntax because **kwargs must come after any *args. def func(kwargs**): is invalid syntax.

3. Final Answer:

   def func(**kwargs): -> Option B

4. Quick Check:

   Double star before kwargs means keyword args [OK]

Hint: Use double star ** before kwargs in function definition [OK]

Common Mistakes:

• Using single star * instead of double star **
• Placing **kwargs incorrectly in parameters
• Writing invalid syntax like kwargs**

3. What will be the output of the following code?

def greet(**kwargs):
    if 'name' in kwargs:
        return f"Hello, {kwargs['name']}!"
    else:
        return "Hello, stranger!"

print(greet(name='Alice'))
print(greet(age=30))

medium

A. Error: KeyError

B. Hello, Alice!\nHello, None!

C. Hello, stranger!\nHello, stranger!

D. Hello, Alice!\nHello, stranger!

Solution

1. Step 1: Analyze function behavior with kwargs

   The function checks if 'name' is a key in kwargs. If yes, it returns a greeting with that name; otherwise, it returns "Hello, stranger!".

2. Step 2: Evaluate each print statement

   First call passes name='Alice', so output is "Hello, Alice!". Second call passes age=30, no 'name' key, so output is "Hello, stranger!".

3. Final Answer:

   Hello, Alice!\nHello, stranger! -> Option D

4. Quick Check:

   Check key in kwargs dict to decide greeting [OK]

Hint: Check if 'name' key exists in kwargs before using it [OK]

Common Mistakes:

• Assuming missing key returns None instead of else case
• Expecting KeyError without checking key presence
• Confusing positional and keyword arguments

4. Identify the error in the following code and choose the correct fix:

def show_info(**kwargs):
    print(kwargs['age'])

show_info(name='Bob')

medium

A. Change **kwargs to *args

B. Remove the print statement

C. Add a default value for 'age' using kwargs.get('age', default)

D. Call show_info with age parameter

Solution

1. Step 1: Identify the error cause

   The function tries to print kwargs['age'], but the call only passes name='Bob'. This causes a KeyError because 'age' key is missing.

2. Step 2: Choose the fix

   Using kwargs.get('age', default) safely returns a default value if 'age' is missing, avoiding the error.

3. Final Answer:

   Add a default value for 'age' using kwargs.get('age', default) -> Option C

4. Quick Check:

   Use kwargs.get() to avoid KeyError on missing keys [OK]

Hint: Use kwargs.get('key', default) to avoid missing key errors [OK]

Common Mistakes:

• Not handling missing keys causing KeyError
• Confusing *args and **kwargs
• Ignoring the need to pass required keys

5. You want to write a function build_profile that accepts a mandatory username and any number of additional keyword arguments describing user info. Which of the following implementations correctly returns a dictionary with all this data?

hard

A. def build_profile(username, **kwargs):
profile = {'username': username}
profile.update(kwargs)
return profile

B. def build_profile(**kwargs, username):
kwargs['username'] = username
return kwargs

C. def build_profile(username, **kwargs):
profile = kwargs
profile['username'] = username
return profile

D. def build_profile(username, *args):
profile = dict(args)
profile['username'] = username
return profile

Solution

1. Step 1: Understand function parameter order

   Mandatory parameters must come before **kwargs. def build_profile(**kwargs, username): kwargs['username'] = username return kwargs is invalid syntax because **kwargs must be last.

2. Step 2: Check dictionary construction

   def build_profile(username, **kwargs): profile = kwargs profile['username'] = username return profile modifies kwargs directly, which can cause unexpected side effects. def build_profile(username, **kwargs): profile = {'username': username} profile.update(kwargs) return profile creates a new dict with username, then updates with kwargs safely.

3. Step 3: Evaluate *args usage

   def build_profile(username, *args): profile = dict(args) profile['username'] = username return profile uses *args which collects positional arguments, not keyword arguments, so it won't work as intended.

4. Final Answer:

   def build_profile(username, **kwargs): profile = {'username': username} profile.update(kwargs) return profile -> Option A

5. Quick Check:

   Use username param first, then update dict with kwargs [OK]

Hint: Put mandatory params before **kwargs and update dict safely [OK]

Common Mistakes:

• Placing **kwargs before mandatory parameters
• Modifying kwargs dict directly
• Using *args instead of **kwargs for keyword data