Re: Callback functions arguments
Peter Otten __pete...@web.de a écrit dans le message de news:mailman.15231.1414399974.18130.python-l...@python.org... Tanks for you answer Python doesn't know it has to pass an argument, it just does it. Change the callback to def maj(): print(no args) and you'll get an error. If I were to guess Yes you are right. I got an error: TypeError: maj() takes 0 positional arguments but 1 was given OK, but i still find very strange the choice of Python's designers to make the Scale behaves like that. The position of the scale is in variable Valeur (StringVar()) which cold be read/write from anywhere, so it is not necessary to pass this variable as an argument to the call back function. If you are looking at the SpinBox widget, in example 4 in the same web site: http://fsincere.free.fr/isn/python/cours_python_tkinter.php boite = Spinbox(Mafenetre,from_=0,to=10,increment=0.5, \ textvariable=Valeur,width=5,command=carre) with the callback function carre def carre(): Calcul du carré Resultat.set(Carré = +str(float(Valeur.get())**2)) you can notice that carre function has no arguments. The value in the SpinBox is catched with Valeur variable. So SpinBox and Scale behaves differently. It is strange. you probably are misled by the 'command=maj' part in the above line. no, I understood this mechanism -- https://mail.python.org/mailman/listinfo/python-list
Re: Callback functions arguments
On Tue, Oct 28, 2014 at 6:35 PM, ast nom...@invalid.com wrote: OK, but i still find very strange the choice of Python's designers to make the Scale behaves like that. That's nothing to do with Python's design. That's all about Tkinter, which presumably is imitating Tk. Python allows the callback function to be called with whatever arguments the caller wishes; you can look at the docs for the different objects to see what args they'll be giving their callbacks. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Callback functions arguments
Chris Angelico ros...@gmail.com a écrit dans le message de news:mailman.15254.1414482690.18130.python-l...@python.org... On Tue, Oct 28, 2014 at 6:35 PM, ast nom...@invalid.com wrote: That's clear to me now. Spinbox and Scale widgets behave differently, that's all. Command on Scale widget: A procedure to be called every time the slider is moved. This procedure will be passed one argument, the new scale value. If the slider is moved rapidly, you may not get a callback for every possible position, but you'll certainly get a callback when it settles Command on Spinbox widget A procedure to be called whenever the scrollbar is moved. No argument is passed. -- https://mail.python.org/mailman/listinfo/python-list
Callback functions arguments
Hi In this web site at example n°5 http://fsincere.free.fr/isn/python/cours_python_tkinter.php A program is using the Scale widget from tkinter module. Here is a piece of code: Valeur = StringVar() echelle = Scale(Mafenetre, from_=-100, to=100, resolution=10, \ orient=HORIZONTAL, length=300, width=20, label=Offset, \ tickinterval=20, variable=Valeur, command=maj) The maj callback function is: def maj(nouvelleValeur): print(nouvelleValeur) When the user move the scale with the mouse, the new position is supposed to be printed on the python shell. The maj function has an argument nouvelleValeur but no argument is passed through the Scale widget. So how the hell Python knows that it has to pass parameter Valeur to the maj function ? thx -- https://mail.python.org/mailman/listinfo/python-list
Re: Callback functions arguments
ast wrote: Hi In this web site at example n°5 http://fsincere.free.fr/isn/python/cours_python_tkinter.php A program is using the Scale widget from tkinter module. Here is a piece of code: Valeur = StringVar() echelle = Scale(Mafenetre, from_=-100, to=100, resolution=10, \ orient=HORIZONTAL, length=300, width=20, label=Offset, \ tickinterval=20, variable=Valeur, command=maj) The maj callback function is: def maj(nouvelleValeur): print(nouvelleValeur) When the user move the scale with the mouse, the new position is supposed to be printed on the python shell. The maj function has an argument nouvelleValeur but no argument is passed through the Scale widget. So how the hell Python knows that it has to pass parameter Valeur to the maj function ? Python doesn't know it has to pass an argument, it just does it. Change the callback to def maj(): print(no args) and you'll get an error. If I were to guess echelle = Scale(Mafenetre, from_=-100, to=100, resolution=10, \ orient=HORIZONTAL, length=300, width=20, label=Offset, \ tickinterval=20, variable=Valeur, command=maj) you probably are misled by the 'command=maj' part in the above line. This means that the function is passed and is different from command=maj() where the *result* of the function is passed. Here's a self-contained example that may clear things up for you: def call_them(one, two): ... one(1) ... two(2, 3) ... def square(a): ... print(a, *, a, =, a*a) ... def product(a, b): ... print(a, *, b, =, a*b) ... call_them(square, product) 1 * 1 = 1 2 * 3 = 6 call_them(product, product) Traceback (most recent call last): File stdin, line 1, in module File stdin, line 2, in call_them TypeError: product() missing 1 required positional argument: 'b' call_them() expects that one() takes 1 argument and two() takes 2 arguments. If the user passes a function that expects a different number of arguments a TypeError is raised. -- https://mail.python.org/mailman/listinfo/python-list
Re: Callback functions arguments
- Original Message - From: ast nom...@invalid.com To: python-list@python.org Sent: Monday, 27 October, 2014 9:16:26 AM Subject: Callback functions arguments Hi In this web site at example n°5 http://fsincere.free.fr/isn/python/cours_python_tkinter.php A program is using the Scale widget from tkinter module. Here is a piece of code: Valeur = StringVar() echelle = Scale(Mafenetre, from_=-100, to=100, resolution=10, \ orient=HORIZONTAL, length=300, width=20, label=Offset, \ tickinterval=20, variable=Valeur, command=maj) The maj callback function is: def maj(nouvelleValeur): print(nouvelleValeur) When the user move the scale with the mouse, the new position is supposed to be printed on the python shell. The maj function has an argument nouvelleValeur but no argument is passed through the Scale widget. So how the hell Python knows that it has to pass parameter Valeur to the maj function ? thx The Scale object is performing the call, hence it will be the Scale object that will call your maj function with a nouvelleValeur parameter. When you write command=maj, you pass the function, but you don't call it. That's the purpose of a callback. You provide a function and it get called by the object you've been giving the function to. The Scale object should be documented and should provide with the callback signature. See http://effbot.org/zone/tkinter-callbacks.htm JM -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. -- https://mail.python.org/mailman/listinfo/python-list
