Instantiate class by passing only a few parameters in Python 3

Question

Good afternoon, everyone

I created a very simple python class with a constructor __init__. The constructor expects to receive 3 parameters, and the 3 have default value. I would like to know how to instantiate the class passing only parameter 1 and 3.

If I charge this way it works :

p = Person('Wagner')

That’s how it works too

p = Person('Wagner','xxx')

But in this way error occurs:

p = Person('Wagner', ,27)

Error:

File "Person.py", line 11
p = Person('Wagner', ,27)
                     ^
SyntaxError: invalid syntax

If I instantiate this way it also works

p = Person('Wagner','' ,27)

but supposing I had 10 parameters with values default and want to pass just the number 7,9,10 as I would ? I would be obliged to pass '' empty, even if they have a default value in the constructor ?

class Person:
    def __init__(self, name='not defined', last_name='not defined', age=0):
        self.name = name
        self.last_name = last_name
        self.age = age

    def printPerson(self):
        print("Name: " + self.name + "\nLast Name: " + 
              self.last_name + "\nAge: " + str(self.age))

Answer 1

You can declare the name of the argument you are passing in Python.

class Person:
    def __init__(self, name = 'not defined', last_name = 'not defined', age = 0):
        self.name = name
        self.last_name = last_name
        self.age = age

p = Person(name = 'Wagner', age = 27)

Answer 2

If you have many arguments that need to be passed to a class, or even a function, it is recommended that you take another approach than positional arguments. Maybe keep nome as a positional (and mandatory) argument and leaving the rest as keyword arguments (and optional):

class Person:
    def __init__(self, name, **kwargs):
        self.name = name
        self.last_name = kwargs.get("last_name", "n/a")
        self.age = kwargs.get("age", 0)

    def __str__(self):
        return f"{self.name} {self.last_name} | {self.age}"

And a basic test:

a = Person("Wagner")
b = Person("Wagner", last_name="Rodrigues")
c = Person("Wagner", age=27)
d = Person("Wagner", last_name="Rodrigues", age=27)

for i in [a, b, c, d]:
    print(i)

Returning:

Wagner n/a | 0
Wagner Rodrigues | 0
Wagner n/a | 27
Wagner Rodrigues | 27

This way new arguments that need to be passed into the class through keywords and in the constructor you define what the default value is if it is omitted.