Positional-Only, Keyword-Only Arguments & Type Hints in Python0%

Positional-Only, Keyword-Only Arguments & Type Hints in Python

Beginner9 min read•Updated: 2026-10-23

🐍 Positional-Only, Keyword-Only Arguments & Basic Type Hints

Modern Python offers precise control over how callers invoke your functions. In Python's official documentation (Section 4.8.3 "Special parameters"), you will encounter function signatures using / (slash) and *`` (asterisk), as well as Type Annotations**.

Let's demystify these modern Python features step by step!

📐 1. Parameter Syntax Overview

A complete Python function signature can look like this:

1def func(pos_only1, pos_only2, /, standard, *, kw_only1, kw_only2):
2         |____________________|    |______|     |__________________|
3            Positional-only        Standard         Keyword-only

Everything before the / must be passed by position only.
Everything *between / and ``** can be passed by position OR keyword.
Everything *after the `` must be passed by keyword only**.

🚫 2. Positional-Only Arguments with `/` (PEP 570)

When you don't want callers using parameter names (e.g., when the parameter name might change or has no semantic meaning to the caller), use /:

1def greet(name, greeting="Hello", /):
2    return f"{greeting}, {name}!"
3 
4# ✅ Correct:
5print(greet("Aarav"))              # "Hello, Aarav!"
6print(greet("Diya", "Namaste"))    # "Namaste, Diya!"
7 
8# ❌ TypeError: greet() got some positional-only arguments passed as keyword arguments: 'name'
9# greet(name="Aarav")

Many built-in Python functions work this way (e.g., len([1, 2, 3]) cannot be called as len(obj=[1, 2, 3])).

🔑 3. Keyword-Only Arguments with `*` (PEP 3102)

When an argument configures behavior or is easy to mix up (such as booleans or options), forcing keyword invocation makes caller code self-documenting:

1def create_user(username, email, *, is_admin=False, send_welcome_email=True):
2    print(f"User: {username}, Admin: {is_admin}, SendEmail: {send_welcome_email}")
3 
4# ✅ Clean & Clear:
5create_user("sumit", "sumit@mskinstitute.in", is_admin=True, send_welcome_email=False)
6 
7# ❌ TypeError: create_user() takes 2 positional arguments but 4 were given
8# create_user("sumit", "sumit@mskinstitute.in", True, False)

🏷️ 4. Basic Type Hints (Python 3.9+)

Python is dynamically typed, but adding Type Hints allows editors like VS Code to catch typos, provide intelligent auto-completion, and document your code:

1def calculate_admission_fee(base_price: float, discount_percent: float = 0.0) -> float:
2    discount_amount = base_price * (discount_percent / 100)
3    return base_price - discount_amount
4 
5total = calculate_admission_fee(4999.0, 10.0)
6print(f"Payable Fee: ₹{total:.2f}")

base_price: float indicates the expected input type.
-> float documents the return type.
Python does not crash if you pass a different type at runtime; type hints are purely advisory and enforced by tools like mypy or IDE linters.

Interactive Quiz• Knowledge Check

Practice Quiz

Question 1

In a function definition def add(a, b, /):, how must the arguments a and b be provided?

Question 2

In def register(name, *, role='student'):, what does the * indicate?

Question 3

What is the return type annotation in def get_status() -> str:?

Question 4

Does the standard Python runtime throw a TypeError automatically if you pass an integer to a function typed def test(x: str):?

Question 5

Which of the following function calls is valid for def query(endpoint, /, *, timeout=30):?

🚀 What's Next?

In the next lesson, we will apply our function mastery to build Project: Calculator (14: Functions).

👉 Continue to Next Lesson: Project: Calculator →

Next Lesson

Project: Calculator

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Scope of Variables in Functions	Project: Calculator

Practice Quiz

Test your understanding of this lesson with 5 questions. Each question has one correct answer.

Previous Next

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Project: Calculator

Positional-Only, Keyword-Only Arguments & Type Hints in Python

Beginner9 min read•Updated: 2026-10-23

Study Materials Cheatsheet

🐍 Positional-Only, Keyword-Only Arguments & Basic Type Hints

Let's demystify these modern Python features step by step!

📐 1. Parameter Syntax Overview

A complete Python function signature can look like this:

1def func(pos_only1, pos_only2, /, standard, *, kw_only1, kw_only2):
2         |____________________|    |______|     |__________________|
3            Positional-only        Standard         Keyword-only

Everything before the / must be passed by position only.
Everything *between / and ``** can be passed by position OR keyword.
Everything *after the `` must be passed by keyword only**.

🚫 2. Positional-Only Arguments with `/` (PEP 570)

When you don't want callers using parameter names (e.g., when the parameter name might change or has no semantic meaning to the caller), use /:

1def greet(name, greeting="Hello", /):
2    return f"{greeting}, {name}!"
3 
4# ✅ Correct:
5print(greet("Aarav"))              # "Hello, Aarav!"
6print(greet("Diya", "Namaste"))    # "Namaste, Diya!"
7 
8# ❌ TypeError: greet() got some positional-only arguments passed as keyword arguments: 'name'
9# greet(name="Aarav")

Many built-in Python functions work this way (e.g., len([1, 2, 3]) cannot be called as len(obj=[1, 2, 3])).

🔑 3. Keyword-Only Arguments with `*` (PEP 3102)

When an argument configures behavior or is easy to mix up (such as booleans or options), forcing keyword invocation makes caller code self-documenting:

1def create_user(username, email, *, is_admin=False, send_welcome_email=True):
2    print(f"User: {username}, Admin: {is_admin}, SendEmail: {send_welcome_email}")
3 
4# ✅ Clean & Clear:
5create_user("sumit", "sumit@mskinstitute.in", is_admin=True, send_welcome_email=False)
6 
7# ❌ TypeError: create_user() takes 2 positional arguments but 4 were given
8# create_user("sumit", "sumit@mskinstitute.in", True, False)

🏷️ 4. Basic Type Hints (Python 3.9+)

Python is dynamically typed, but adding Type Hints allows editors like VS Code to catch typos, provide intelligent auto-completion, and document your code:

1def calculate_admission_fee(base_price: float, discount_percent: float = 0.0) -> float:
2    discount_amount = base_price * (discount_percent / 100)
3    return base_price - discount_amount
4 
5total = calculate_admission_fee(4999.0, 10.0)
6print(f"Payable Fee: ₹{total:.2f}")

base_price: float indicates the expected input type.
-> float documents the return type.
Python does not crash if you pass a different type at runtime; type hints are purely advisory and enforced by tools like mypy or IDE linters.

Interactive Quiz• Knowledge Check

Practice Quiz

Question 1

In a function definition def add(a, b, /):, how must the arguments a and b be provided?

Question 2

In def register(name, *, role='student'):, what does the * indicate?

Question 3

What is the return type annotation in def get_status() -> str:?

Question 4

Does the standard Python runtime throw a TypeError automatically if you pass an integer to a function typed def test(x: str):?

Question 5

Which of the following function calls is valid for def query(endpoint, /, *, timeout=30):?

🚀 What's Next?

In the next lesson, we will apply our function mastery to build Project: Calculator (14: Functions).

👉 Continue to Next Lesson: Project: Calculator →

Next Lesson

Project: Calculator

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Scope of Variables in Functions	Project: Calculator

Practice Quiz

Test your understanding of this lesson with 5 questions. Each question has one correct answer.

Previous Next

🐍 Positional-Only, Keyword-Only Arguments & Basic Type Hints

📐 1. Parameter Syntax Overview

🚫 2. Positional-Only Arguments with / (PEP 570)

🔑 3. Keyword-Only Arguments with * (PEP 3102)

🏷️ 4. Basic Type Hints (Python 3.9+)

Practice Quiz

🚀 What's Next?

Project: Calculator

Related Lessons

Practice Quiz

Loading Page Content...

🐍 Positional-Only, Keyword-Only Arguments & Basic Type Hints

📐 1. Parameter Syntax Overview

🚫 2. Positional-Only Arguments with / (PEP 570)

🔑 3. Keyword-Only Arguments with * (PEP 3102)

🏷️ 4. Basic Type Hints (Python 3.9+)

Practice Quiz

🚀 What's Next?

Project: Calculator

Related Lessons

Practice Quiz

🚫 2. Positional-Only Arguments with `/` (PEP 570)

🔑 3. Keyword-Only Arguments with `*` (PEP 3102)

🚫 2. Positional-Only Arguments with `/` (PEP 570)

🔑 3. Keyword-Only Arguments with `*` (PEP 3102)