Why did I get a "None" value of the parameter in subclass?-CodePudding

I'm new to python (and coding) and I've been trying to expand my knowledge by youtube tutorials. When watching a chapter about classes I have created a class and a sub class and I don't know why I get the results as they are. Can you help me?

This is my code:

class Person:
    def __init__(self, name, age, height):
        self.name = name
        self.age = age
        self.height = height

    def print_info(self):
        print(self.name   ", age "   self.age   ", height "   self.height   "cm.")


class Employee(Person):
    def  __init__(self, name, age, height, id_number):
        Person.__init__(self, name, age, height)
        self.id_number = id_number

    def print_employee_info(self):
        print(str(Person.print_info(self))   self.id_number)

john = Employee("John", "20", "182", "2230")
john.print_employee_info()

I expected it to print:

"John, age 20, height 182cm.2230"

What I got is:

"John, age 20, height 182cm 
None2230"

So I believe it that it prints in new line "None2230" because I call the method Person.print_info(self) ?

What I don't know is why there is "None" added to id_number and how can I fix this?

If anything else bothers you, just write it down I'd like to learn.

Thanks a lot for the answers.

Much appreciated.

CodePudding user response：

You want your print_info method to return a string rather than printing it. Try changing it to this:

    def print_info(self):
        return self.name   ", age "   self.age   ", height "   self.height   "cm."

Then your print_employee_info can just be

    def print_employee_info(self):
        print(self.print_info()   self.id_number)

CodePudding user response：

print_info(self) does not return anything (returns None). If you want your code to work you should do soemthing like:

def get_info(self):
    return self.name   ", age "   self.age   ", height "   self.height   "cm."

and then

def get_employee_info(self):
    return str(Person.print_info(self))   self.id_number

Finally, to use this, call:

print(john.get_employee_info())

CodePudding user response：

Both your print_* methods look like they should be converted to __str__ methods.

class Person:
    def __init__(self, *, name, age, height, **kwargs):
        super().__init__(**kwargs)
        self.name = name
        self.age = age
        self.height = height

    def __str__(self):
        return f'{self.name}, age {self.age}, height {self.height} cm'


class Employee(Person):
    def  __init__(self, *, id_number, **kwargs):
        super().__init__(**kwargs)
        self.id_number = id_number

    def __str__(self):
        return super().__str__()   self.id_number


john = Employee(name="John", age="20", height="182", id_number="2230")
print(john)

Try to push I/O "up" as far as possible in your code. If your method can return a string for someone else to print rather than printing it itself, do it.