在类的 str() 函数中使用实例名称

Question

I wrote a class about points in cartesian system (each point instance having abscissa and ordinate) and each instance has its name, for example we have point 'A' (coordinates (2,3)) and 'B'(coordinates(1,2)). In the str () function i need to use the name of the instance to have a nice output. For example i need the program to print out ( Abscissa of A is 2) when using the print command (print(A)) And displaying ( Abscissa of B is 1) when (print(B)) is written in main script. The main problem is to have the name of instance displayed. Is there a function that returns the name of instance of a certain class?

I tried using self.namehex(id(self)) in the init() function and then use self.name() but it didn't do the trick

Answer 1

As @chepner commented, objects don't know the names they're assigned.

If you want your Point class to know its instance name, add it as an argument to __init__() .

class Point(object):
    def __init__(self, name, x, y):
        self.name = name
        ...

    def __str__(self):
        return 'abcissa of %s is ...' % self.name

a = Point('a', 50, 100)

Answer 2

You need to implement the repr or str method. repr is used when you use print on the object and str when you use str(object).

class SomeClass:

def __init__(self, name, x, y):
    self.name = name
    self.x = x
    self.y = y

def __repr__(self):
    return f'abscissa of name: {self.name}  is...'

def __str__(self):
    return f'abscissa of name: {self.name}  is...'

OUTPUT:

a = SomeClass('name', 4, 6) b = SomeClass('name2', 9, 8)

a abscissa of name: name is... b abscissa of name: name2 is... str(a) 'abscissa of name: name is...' str(b) 'abscissa of name: name2 is...'