Why is the function called before pressing a button?

Question

My program draws the fractal using pointSize_max and pointSize variables, which are entered by the user in Tkinter. The problem is that the fractal is drawn before pressing a button (as soon as the program is run), and the program does not draw the fractal when the button is pressed.

pointLabel = tk.Label(frame,text="minimaalne pikkus")
pointLabel.pack()
pointSize = tk.StringVar()
pointEntry = tk.Entry(frame,textvariable=pointSize)
pointEntry.pack()
pointSize.set(str(10))

pointLabel_max = tk.Label(frame,text="maksimaalne pikkus")
pointLabel_max.pack()
pointSize_max = tk.StringVar()
pointEntry_max = tk.Entry(frame,textvariable=pointSize_max)
pointEntry_max.pack()
pointSize_max.set(str(30))

drawButton = tk.Button(frame, text = "Draw a fractal", command=koch(int(pointSize_max.get()), int(pointSize.get())))

# koch function draws the fractal 

drawButton.pack()

tk.mainloop()

score 0 · Accepted Answer · answered Apr 07 '15 at 16:18

0

The koch function is called when the button is created, as part of the parameter evaluation before the tk.Button call. You can create a function object to call instead.

def koch_invoke():
    koch(int(pointSize_max.get()), int(pointSize.get()))
drawButton = tk.Button(frame, text = "Draw a fractal", command=koch_invoke)

answered Apr 07 '15 at 16:18

Mark Ransom

299,747
42
398
622

Thank you! But now button does not appear. – Kostya Apr 07 '15 at 16:30
@user2690370 that's a different question I'm afraid. Does the button appear if you leave off the `command`? – Mark Ransom Apr 07 '15 at 16:35
I have found the problem. Thank you very much for your help! – Kostya Apr 07 '15 at 16:36

score 0 · Answer 2 · answered Apr 07 '15 at 16:20

When your script is compiled it comes to this line and runs the function since you are calling it:

command=koch(int(pointSize_max.get()), int(pointSize.get()))

Try using a lambda to prevent this from happening:

command= lambda x = int(pointSize_max.get()), y = int(pointSize.get()): koch(x, y))

Why is the function called before pressing a button?

2 Answers2