About tkinter Canvas does not display pictures

Problem description

Originally intended to use tkinter To develop a " Spider card " game , But testing tkinter.Canvas Create an image on without displaying the image .

The test code is as follows :

from tkinter import *
from tkinter import ttk
from PIL import ImageTk, Image

class SpiderSolitaire(ttk.Frame):
    def __init__(self, master: Tk, **kw):
        super().__init__(master, **kw)

        self.mainframe = ttk.Frame(master)
        self.mainframe.grid(column=0, row=0, sticky=NSEW)

        self.canvas = Canvas(self.mainframe, width=400, height=300, background='gray55')
        self.canvas.grid(row=0, column=0, sticky=NS)
        im = ImageTk.PhotoImage(Image.open('./images/Spades_1.png'))
        self.canvas.create_image(30, 10, image=im, anchor='nw')
        #  These two lines are only used to indicate where the picture is to be displayed .
        self.canvas.create_line(30, 10, 98, 113, fill='red', width=3)   
        self.canvas.create_line(30, 113, 98, 10, fill='red', width=3)  
        
        # set window's title.
        self.master.title('Spider Solitaire')
        # set window's geometry size
        self.master.geometry('400x300')

if __name__ == '__main__':
    root = Tk()
    SpiderSolitaire(root)
    root.mainloop()

The operation results are as follows , The picture doesn't show up .

stay stackoverflow Found the same problem description on , There is a feasible solution . But there is no explanation for this problem . In other articles, there is a problem of memory recycling , This statement is relatively reliable .

resolvent

Assign the imported image to a " Persistent variables ", For example, create a self.image Used to hold imported PhotoImage, In this way, the pictures will not be recycled as garbage . If there are multiple pictures, you can create a list to hold .

Modify the above test code as follows :

from tkinter import *
from tkinter import ttk
from PIL import ImageTk, Image

class SpiderSolitaire(ttk.Frame):
    def __init__(self, master: Tk, **kw):
        super().__init__(master, **kw)

        self.mainframe = ttk.Frame(master)
        self.mainframe.grid(column=0, row=0, sticky=NSEW)

        self.canvas = Canvas(self.mainframe, width=400, height=300, background='gray55')
        self.canvas.grid(row=0, column=0, sticky=NS)
        # bug fixed:  Modify the following two lines .
        self.image = ImageTk.PhotoImage(Image.open('./images/Spades_1.png'))
        self.canvas.create_image(30, 10, image=self.image, anchor='nw')
        #  These two lines are only used to indicate where the picture is to be displayed .
        self.canvas.create_line(30, 10, 98, 113, fill='red', width=3)   
        self.canvas.create_line(30, 113, 98, 10, fill='red', width=3)  
        
        # set window's title.
        self.master.title('Spider Solitaire')
        # set window's geometry size
        self.master.geometry('400x300')

if __name__ == '__main__':
    root = Tk()
    SpiderSolitaire(root)
    root.mainloop()

The operation results are as follows , If the film is indeed shown !o(￣▽￣)ブ

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