Why does passing tuple as arg WITHOUT scattering work?

Ethan Furman ethan at stoneleaf.us
Wed Oct 21 01:00:33 CEST 2009


MRAB wrote:
> Alf P. Steinbach wrote:
> 
>> Hi all.
>>
>> I'm just learning Python from scratch, on my own. Apologies if this 
>> question is too newbie... Or perhaps answered in some FAQ (where?).
>>
>> Here's my original code for simple starter program, using the 
>> ActivePython implementation in Windows XP Prof, Python version is 2.6:
>>
>>
>> <code>
>> import Tkinter
>>
>> window = Tkinter.Tk()
>> window.title( "A fixed size ellipse..." )
>> window.geometry( "350x200" )            # Client area size, not window 
>> size.
>> window.resizable( width = 0, height = 0 )
>>
>> canvas = Tkinter.Canvas( window, bg = "white" )
>> bbox = 2, 2, 347, 197                   # Pixel coors left, top, 
>> right, bottom
>> canvas.create_oval( bbox, fill = "PeachPuff" )
>> canvas.pack()                           # Fill the entire client area, 
>> please.
>>
>> window.mainloop()                       # Process events until window 
>> is closed.
>> </code>
>>
>>
>> It worked nicely, and I thought this code was fairly perfect until I 
>> started studying the language reference.
>>
>> It seems that formally correct code should apply the scatter operator 
>> to the tuple, like this:
>>
>>
>> canvas.create_oval( *bbox, fill = "PeachPuff" )
>>
>>
>> And this /also/ works nicely!
>>
>> I think it's this latter that is correct, and that the former just 
>> worked by accident, due to e.g. the way that some C function parses 
>> arguments or such?
>>
>> But I'm unable to figure it out, so, what's correct (both? one?), and 
>> assuming it's the latter that's correct, would the first version still 
>> work in practice regardless of Python / Tkinter implementation?
>>
> I've looked at the source in Tkinter.py. The positional arguments are
> collected and then flattened into a tuple (tuples and lists are
> 'scattered').

Huh.  I would have said 'gathered'.  Must be my FoxPro days sneaking up 
on me.  *Shudder*

~Ethan~



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