如何从类调用启动函数

Question

I am learning to use classes and I would like to call my GetWeather class from another MainApplication class.

Upon calling GetWeather.coords I want to to start with a function that receives the required data.

Below is my code so far:

API_ID = '///foo///'

class GetWeather:
    def __init__(self, city, country):
        url_city = 'http://api.openweathermap.org/data/2.5/weather?q={},{}&appid={}'.format(city, country, API_ID)
        weatherdata = requests.get(url_city).json()
    def coords(self):
        print(weatherdata)

class MainApplication:
    def __init__(self, master):
        self.master = master
        self.frame = tk.Frame(self.master)


        self.button1 = tk.Button(self.frame, text = 'Coords', width = 25, command = GetWeather.coords('town','country'))
        self.button1.pack()


        self.frame.pack()



def main():
    root = tk.Tk()
    app = MainApplication(root)
    root.mainloop()

if __name__ == "__main__":
    main()

Answer 1

To create an instance of a class, call it like as if it were a function that just so happened to return a GetWeather object.

Also, the argument to tkinter.Button 's command should be something it can call again, meaning you should pass it a function that hasn't been called yet. Note the missing parentheses after GetWeather('town','country').print_coords .

Here's your fixed code:

import tkinter as tk

import requests

API_ID = '///foo///'

class GetWeather:

    def __init__(self, city, country):
        url_city = 'http://api.openweathermap.org/data/2.5/weather?q={},{}&appid={}'.format(city, country, API_ID)
        # note: save the weather data in 'self'
        self.weatherdata = requests.get(url_city).json()

    def print_coords(self):
        # get the stored weather data
        print(self.weatherdata)


class MainApplication:

    def __init__(self, master):
        self.master = master
        self.frame = tk.Frame(self.master)

        self.button1 = tk.Button(
            self.frame, text='Coords', width=25, 
            command=GetWeather('town', 'country').coords,
        )
        self.button1.pack()

        self.frame.pack()


def main():
    root = tk.Tk()
    app = MainApplication(root)
    root.mainloop()

if __name__ == "__main__":
    main()

Answer 2

There's nothing preventing you from doing that, but you do have make sure the function has the information it need available. Since coords() is a method of class GetWeather , this can be done by simply saving the values passed to it when an instance of the class is created, then using it.

Below is an example code showing how to do that, and it will call the function to retrieve the data each time the Button is clicked (unlike @GeeTransit's answer which only retrieves the data once when button1 is initially created).

API_ID = '///foo///'

class GetWeather:
    def __init__(self, city, country):
        self.city = city
        self.country = country

    def coords(self):
        url_city = ('http://api.openweathermap.org/data/2.5/weather?'
                    'q={},{}&appid={}'.format(self.city, self.country, API_ID)
        weatherdata = requests.get(url_city).json()  # Call function to get data.
        print(weatherdata)


class MainApplication:
    def __init__(self, master):
        self.getweather = GetWeather('town', 'country')
        self.master = master
        self.frame = tk.Frame(self.master)
        self.button1 = tk.Button(self.frame, text='Coords', width=25,
                                 command=self.getweather.coords)
        self.button1.pack()
        self.frame.pack()


def main():
    root = tk.Tk()
    app = MainApplication(root)
    root.mainloop()

if __name__ == "__main__":
    main()