Cannot pass arguments from the tkinter widget.after function

Question

Part of the GUI I'm building using tkinter has a pop-up window that says "Please wait while the program is running." then after it finishes the window goes away. I'm using the widget.after command to open the window and run the command. However if I pass the function I call arguments then the pop up window never occurs. Here's an example:

def backupWindow
    self.restoreCB = Toplevel()

    message = "Please wait while backup runs"
    Label(self.restoreCB, text=message, padx=100, pady=20).pack()

    widget.after(10, self.runBackup)

def runBackup(self):
    <backup code>
    self.backupCB.destroy()

This runs fine and does what I want it to do, the window pops up while the backup runs, then the window closes after the backup. However, If I pass the and argument from the widget.after like the code below, the "please wait" message never shows up.

def backupWindow
    self.restoreCB = Toplevel()

    message = "Please wait while backup runs"
    Label(self.restoreCB, text=message, padx=100, pady=20).pack()

    widget.after(10, self.runBackup(mybackup))

def runBackup(self,mybackup):
    <backup code using mybackup>
    self.backupCB.destroy()

Bryan Oakley · Accepted Answer · 2017-08-21 11:41:17Z

42

When you do this:

widget.after(10, self.runBackup(mybackup))

... You are telling Tkinter "run the command runBackup, and when it returns, use the result as an argument to after". Because runBackup returns None, the above is equivalent to:

self.runBackup(mybackup)
widget.after(10, None)

Instead, you want to give after a reference to the function, rather than calling the function. If the command needs arguments, those can be given to after as additional arguments.

For example:

widget.after(10, self.runBackup, mybackup)

edited Aug 21, 2017 at 11:41

answered Jun 14, 2012 at 22:47

Bryan Oakley

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1 Comment

l4mpi Over a year ago

just for completeness, the resulting call is widget.after(10, None) because a function that has no return statement returns None.

John Gaines Jr. · Accepted Answer · 2012-06-14 19:55:09Z

1

I would try functools.partial to wrap your call as in:

widget.after(10, functools.partial(self.runBackup, mybackup))

Or you could define a local function that takes no arguments but passes the parameter (which is in essence what functools.partial does).

answered Jun 14, 2012 at 19:55

John Gaines Jr.

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2 Comments

Bryan Oakley Over a year ago

While this is a perfectly acceptable solution, it's more complex than it needs to be. after is designed to take arguments, and use them when calling the function, the OP was just doing it wrong.

l4mpi Over a year ago

in this simple case you could just use a lambda to define an anonymous function instead of functools.partial: widget.after(10, lambda: self.runBackup(mybackup))

MVPimenta · Accepted Answer · 2019-04-24 21:18:25Z

0

Add: Using Lambda function format, the function doesn´t fail after several recursive calls. eg:

Function abc(par):
           stat-1
           stat-2
           ...
           stat-n
           root.after(1000, lambda : abc(par))

    ...

(it´s very useful to update a time-clock at left-top of window, for example...)

answered Apr 24, 2019 at 21:18

MVPimenta

1

1 Comment

Ghislain Bugnicourt Over a year ago

Do you mean that .after(1000, lambda : abc(par)) is better for recursive calls than .after(1000, abc, par) ? Genuine question.

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