How to implement a mouse hovering callback on canvas items in tkinter?

You can pass the argument activefill when creating your rectangle.

From effboot.org:

Fill color to use when the mouse pointer is moved over the item, if different from fill.

To do so, replace:

rectangle = self.canvas.create_rectangle(x, y, x + 50, y + 50, fill='red')

By:

rectangle = self.canvas.create_rectangle(x, y, x + 50, y + 50, fill='red', activefill='cyan')

This removes the need to bind Motion to your canvas, and also makes the code noticebly shorter:

from tkinter import *import numpy as npclass rect:    def __init__(self, root):        self.root = root        self.size = IntVar()        self.canvas = Canvas(self.root, width=800, height=300)        self.scale = Scale(self.root, orient=HORIZONTAL, from_=3, to=20, tickinterval=1, variable=self.size)        self.scale.bind('<ButtonRelease>', self.show)        self.board = []        self.array = np.zeros((self.scale.get(),self.scale.get())).tolist()        self.canvas.pack()        self.scale.pack()    def show(self,event):        self.canvas.delete('all')        x = 50        y = 50        row = []        self.board.clear()        for i in range(self.scale.get()):            row = []            for j in range(self.scale.get()):                rectangle = self.canvas.create_rectangle(x, y, x + 50, y + 50, fill='red', activefill='cyan')                x += 50                row.append(rectangle)            x -= j*50            y +=50            self.board.append(row)        print(self.board)root = Tk()a = rect(root)root.mainloop()

I changed motion method and added self.last = None to __init__ method:

from tkinter import *import numpy as npclass rect:    def __init__(self, root):        self.root = root        self.size = IntVar()        self.canvas = Canvas(self.root, width=800, height=300)        self.scale = Scale(self.root, orient=HORIZONTAL, from_=3, to=20, tickinterval=1, variable=self.size)        self.scale.bind('<ButtonRelease>', self.show)        self.canvas.bind('<Motion>', self.motion)        self.board = []        self.array = np.zeros((self.scale.get(),self.scale.get())).tolist()        self.canvas.pack()        self.scale.pack()        self.last = None    def motion(self, event):        temp = self.canvas.find_withtag(CURRENT)        if temp == self.last:            self.canvas.itemconfig(CURRENT, fill="cyan")            self.canvas.update_idletasks()        else:            self.canvas.itemconfig(self.last, fill="red")        self.last = temp    def show(self,event):        self.canvas.delete('all')        x = 50        y = 50        row = []        self.board.clear()        for i in range(self.scale.get()):            row = []            for j in range(self.scale.get()):                rectangle = self.canvas.create_rectangle(x, y, x + 50, y + 50, fill='red')                x += 50                row.append(rectangle)            x -= j*50            y +=50            self.board.append(row)        print(self.board)root = Tk()a = rect(root)root.mainloop()