调用前一个类的方法

Question

I'm trying to call a method from a previous Class for the Class I'm currently working on. It's a mock GPS system using classes for different things. The class I'm trying to get the method from looks like the following :

class GPS_POI:
    def __init__(self, location, name , kind):
        self.location= location
        self.name = str(name)
        self.kind = str(kind) 

    def __str__ (self):
        return (str(self.location) + ": "+ self.name +", " + self.kind )

The current class and method I am working on:

class GPS :
    def __init__ (self, current, map = None):
        self.current = current
        self.map= map
        self.route= []

     def display_map(self):

        for i in self.route:
            display= GPS_POI()
            return (display.__str__ + "\n")

When I run it, I just end up getting the result of "None" when the output I want (example) would be :

"(3,1): kmart, clothes \\n(2,3): burger king, food\\n" etc.

Would I need to include my parameter self.map from the class GPS into the display_map function for it work properly? What am I not understanding about calling a method from a previous class?

Answer 1

You aren't calling display.__str__ ; you are just referencing it. You shouldn't call __str__ explicitly anyway. Its purpose is to provide a hook for when you try to treat the object as a string, such as when passing it to str as an argument:

return str(display) + "\n"