Pass a function as a class function through constructor in python

Question

I am trying to make a class in python that lets you pass the executed onclick code through the constructor. So far:

import tkinter as tk
import PIL
from PIL import ImageTk, Image

class closeIcon:
  path = ""
  width = 0
  height = 0
  xpos = 0
  ypos = 0
  onclick = 0
  canv = ""

  def __init__(self, path, width, height, xpos, ypos, onclick, canv):
    self.path = path
    self.width = width
    self.height =  height
    self.xpos = xpos
    self.ypos = ypos
    self.onclick = onclick
    self.canv = canv
    self.img = Image.open(self.path).resize((self.width, self.height), Image.ANTIALIAS)
    self.img_ = ImageTk.PhotoImage(self.img)
    self.label = tk.Label(self.canv, image=self.img_, bg=self.canv["background"])
    self.label.place(x=xpos, y=ypos)
    self.label.bind("<Button-1>", self.onclick)

Example of how I would instanciate an object from that class:

closeAppIcon = closeIcon("assets/cross1.png", 30, 30, winWidth-45, 10, {print("Hello")}, canvas_)

But whenever I run the application I am getting an Hello in the console without even clicking on the image, and when I click on the image I get following error message:

Exception in Tkinter callback Traceback (most recent call last): File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.8_3.8.1776.0_x64__qbz5n2kfra8p0\lib\tkinter_init_.py", line 1883, in call return self.func(*args) TypeError: 'set' object is not callable

What am I doing wrong?

{print("Hello")} is a set containing the element None. Did you mean to pass a function? — khelwood
– khelwood, Commented Nov 1, 2020 at 9:50

khelwood · Accepted Answer · 2020-11-01 10:08:41Z

4

{print("Hello")} is a set containing the element None. Your code expects a function in that place. If you want to pass a function containing the statement print("Hello"), you could use:

lambda *args: print("Hello")

This defines a function that will accept any number of positional arguments and print "Hello".

edited Nov 1, 2020 at 10:08

answered Nov 1, 2020 at 9:51

khelwood

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4 Comments

Nicolas Stadler Over a year ago

Now Im getting the error "<lambda>() takes 0 positional arguments but 1 was given"

khelwood Over a year ago

Try using lambda *args: instead of lambda:

khelwood Over a year ago

lambda: indicates a function that receives no arguments. lambda *args: indicates a function that can receive any number of positional arguments. Evidently the particular callback here (onclick) requires a function that accepts one argument.

Bryan Oakley Over a year ago

When you bind a function to an event, the function is always called with one argument, which is an object representing the event that triggered the callback.

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