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Positional Arguments

16. Positional Arguments#

def add(operand_1, operand_2):
    print(f"The sum of {operand_1} and {operand_2} is {operand_1 + operand_2}")

Yipeee! we have created a new function called add which is expected to add two integers values, Just kidding 😜, thanks to the dynamic typing of the Python, we can even add float values, concat strings and many more using our add function, but for now, let’s stick with the addition of integers 😎

add(1, 3)

The sum of 1 and 3 is 4

Yup, we did got our result ⭐️. what if I forget passing a value? we would see a TypeError exception raised 👻

add(1)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[3], line 1
----> 1 add(1)

TypeError: add() missing 1 required positional argument: 'operand_2'

The name Positional arguments itself says the arguments should be according to the function signature. But here’s a deal, we can change the order of arguments being passed, just that we should pass them with the respective keyword 🙂

Example

def difference(a, b):
    print(f"The difference of {b} from {a} is {a - b}")

difference(5, 8)

The difference of 8 from 5 is -3

difference(b=8, a=5)  # Positions are swapped, but passing the objects as keywords.

The difference of 8 from 5 is -3

We can see in the above example that even if the positions are changed, but as we have are passing them through keywords, the result remains the same. ⭐️

16.1. Position only arguments#

We do have the power ✊ to make the user call the function’s position only arguments the way we want, Thanks to PEP-570 for Python >= 3.8

The syntax defined by the PEP-570 regarding Position only arguments is as:

def name(positional_only_parameters, /, positional_or_keyword_parameters, *, keyword_only_parameters):

def greet(greet_word, /, name_of_the_user):
    print(f"{greet_word} {name_of_the_user}!")

In the above example, we do have two arguments greet_word and name_of_the_user we used / to say that Hey Python! Consider greet_word as Positional only Argument

When we try to call our function greet with greet_word as keyword name, Boom 💣, we get a TypeError exception.

greet(greet_word="Hello", name_of_the_user="Pythonist")

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[8], line 1
----> 1 greet(greet_word="Hello", name_of_the_user="Pythonist")

TypeError: greet() got some positional-only arguments passed as keyword arguments: 'greet_word'

Try to call our greet with greet_word as positional only argument, meaning not passing it by keyword name. We can hope that there won’t be any exception raised. 😁

# Calling greet function with name_of_the_user as Positional keyword.
greet("Hello", "Pythonist")

# Calling greet function with name_of_the_user with keyword name.
greet("Hello", name_of_the_user="Pythoneer😍")

Hello Pythonist!
Hello Pythoneer😍!
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