Deep Dive into Positional, Keyword, and Variable-Length Arguments in Python

When working with Python functions, you might come across scenarios where you need to handle a varying number of arguments or pass arguments using special syntax. In such cases, the * and / symbols can be used to handle special parameter passing. In this tutorial post, we will explore how to use these special parameters and discuss their applications in Python functions. Additionally, we will delve into the usage of the join() function, which is a handy string manipulation tool in Python.

Overview of Special Parameters in Python

Special parameters in Python provide flexibility in function parameter passing. They allow handling varying numbers of arguments or specifying keyword-only and positional-only arguments. This section introduces the concept of special parameters and their significance in Python functions.

Understanding the Asterisk (*) Syntax

The asterisk () symbol has versatile applications when it comes to function parameter passing. This section covers the various use cases of the asterisk (*) syntax, including handling positional arguments, unpacking iterables, and combining both.

Positional Arguments with (*)

The asterisk (*) syntax can be used to handle an arbitrary number of positional arguments in a function. For example:

def sum_numbers(*args):
total = 0
for num in args:
total += num
return total

result = sum_numbers(1, 2, 3, 4)
print(result) # Output: 10

Unpacking Iterable with (*)

The asterisk (*) syntax can also be used to unpack an iterable and pass its elements as separate arguments to a function. For example:

def sum_numbers(*args):
total = 0
for num in args:
total += num
return total

numbers = [1, 2, 3, 4]
result = sum_numbers(*numbers)
print(result) # Output: 10

Combining Positional and Unpacking with (*)

The asterisk (*) syntax can be combined with positional arguments to handle a mix of fixed and varying arguments. For example:

def greet(name, *messages):
for msg in messages:
print(f”{name}, {msg}!”)

greet(“John”, “Hello”, “How are you?”, “Nice to meet you!”)


John, Hello!

John, How are you?

John, Nice to meet you!

Keyword-Only Arguments with (*)

The asterisk (*) syntax allows defining keyword-only arguments, which can only be passed using their respective parameter names. For example:

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

greet(name=”John”) # Output: Hello, John!


def greet(*, name, message):
print(f”{message}, {name}!”)

greet(name=”John”, message=”Hello”) # Output: Hello, John!

In this example, the function greet() has two keyword-only arguments: name and message. These arguments can only be passed using their respective parameter names. By specifying name="John" and message="Hello" when calling the function, we get the output “Hello, John!”.

This demonstrates how keyword-only arguments can be useful when you want to enforce explicit naming of certain arguments in function calls.

Introducing the Slash (/) Syntax

In Python 3.8 and later versions, the slash (/) syntax was introduced to denote positional-only arguments. This section explains the usage of the slash (/) syntax and its implications for function arguments.

Positional-Only Arguments with (/)

Positional-only arguments are defined using the / symbol in the function signature. It indicates that the parameters preceding the / can only be passed positionally and not as keyword arguments. This feature was introduced in Python 3.8 to provide more control over argument passing in functions.

def divide_numbers(dividend, /, divisor):
return dividend / divisor

result = divide_numbers(10, 2)
print(result) # Output: 5.0


def greet(name, /, message=”Hello”):
print(f”{message}, {name}!”)

greet(“John”) # Output: Hello, John!
greet(“Alice”, “Hi”) # Output: Hi, Alice!

In this example, the greet() function has two parameters: name and /, with an optional default value for message set to “Hello”. The / symbol indicates that name can only be passed positionally. When calling greet("John"), the value “John” is assigned to name because it is passed as a positional argument. The default value “Hello” is used for message. The function then prints the greeting message “Hello, John!”.

In the second function call greet("Alice", "Hi"), both name and message are provided positionally. Hence, “Alice” is assigned to name, and “Hi” is assigned to message. The function prints the greeting message “Hi, Alice!”.

These examples demonstrate how to use the / symbol to define positional-only arguments in Python functions. By doing so, you have more control over how arguments are passed and can enforce specific argument passing patterns in your functions.


def calculate(a, b, c, /):
return a + b – c

result = calculate(10, 5, 3)
print(result) # Output: 12

In this example, the calculate() function takes three arguments: a, b, and c. The / symbol is used to indicate that all three arguments must be passed positionally and cannot be passed as keyword arguments. When calling calculate(10, 5, 3), the values 10, 5, and 3 are assigned to a, b, and c, respectively. The function performs the calculation a + b - c and returns the result, which is 12.

Combining Keyword-Only(*) and Positional-Only with (/)

By using / and * together, you can create functions that have a mix of positional-only arguments, variable-length positional arguments, keyword-only arguments, and variable-length keyword arguments, allowing for more flexible and versatile function signatures.

def calculate(a, b, /, operation=”+”, *numbers, **options):
result = 0

if operation == “+”:
result = sum(numbers) + a + b
elif operation == “*”:
result = a * b
for num in numbers:
result *= num

print(f”Result: {result}”)
print(f”Options: {options}”)

In this example, the calculate() function has the following argument structure:

  • a and b are positional-only arguments defined before the / symbol.
  • operation is a keyword-only argument defined after the / symbol, with a default value of “+”.
  • *numbers is a variable-length argument that collects any additional positional arguments beyond a, b, and operation into a tuple.
  • **options is a variable-length keyword argument that collects any additional keyword arguments into a dictionary.

Let’s see how this function can be called:

calculate(2, 3, 4, 5, operation=”*”, key1=”value1″, key2=”value2″)


Result: 120
Options: {‘key1’: ‘value1’, ‘key2’: ‘value2’}

In this example, we pass 2 and 3 as positional arguments for a and b, respectively. The additional positional arguments 4 and 5 are collected in the numbers tuple. The keyword argument operation is set to "*", and any additional keyword arguments key1 and key2 are collected in the options dictionary.

Based on the provided operation (in this case, “*”), the function performs the calculation and prints the result, which is 120. The options dictionary contains any additional keyword arguments passed to the function.

Exploring the join() Function in Python

The join() function is a powerful string manipulation tool in Python. It allows us to concatenate elements of an iterable into a single string using a specified separator. This section provides a comprehensive overview of the join() function, including its syntax, usage with strings and lists, customization with separators, and handling non-string elements.

Syntax of join()

The join() function is called on a string separator and takes an iterable as its argument. The syntax is as follows:


Joining Strings with join()

The join() function can be used to concatenate a list of strings into a single string with a specified separator. For example:

names = [“John”, “Alice”, “Bob”]
joined_names = “, “. join(names)
print(joined_names) # Output: John, Alice, Bob

Joining Lists with join()

The join() function can also be used to concatenate a list of elements into a single string. However, the elements must be strings. For example:

numbers = [1, 2, 3, 4]

Convert the list of numbers to strings before joining

joined_numbers = “, “. join(str(num) for num in numbers)
print(joined_numbers) # Output: 1, 2, 3, 4

Custom Separator with join()

The join() function allows customization of the separator used to join the elements. For example:

words = [“Hello”, “World”]
custom_separator = ” – “
joined_words = custom_separator.join(words)
print(joined_words) # Output: Hello – World


In this tutorial post, we explored the usage of special parameters * and / in Python function calls. We learned how to handle varying numbers of arguments and specify keyword-only and positional-only arguments. Additionally, we discussed the join() function, which is a powerful tool for concatenating strings and customizing the joining process. By mastering these concepts, you can enhance your Python programming skills and write more flexible and efficient code.

Feel free to customize the examples or add more content to each section to suit your requirements.