[Tutor] jumping from function to function

[spir]

Le Sat, 31 Jan 2009 00:30:18 +0800,
David <ldl08 at gmx.net> a écrit :

> Dear List,
> 
> the following comes from Harrington's "Hands-on Python" (section 
> 1.11.8): http://www.cs.luc.edu/~anh/python/hands-on/
> 
> 
> <code>
> 
> '''Avoiding any error by passing a parameter'''
> 
> def main():
>      x = 3
>      f(x)
> 
> def f(whatever):
>      print whatever
> 
> main()
> 
> </code>
> 
> I am not quite sure what is going on here. Could you please correct my 
> line of thought?
> 
> 1) main() calls the function def main():
> 
> 2) in function def main(): the actual parameter 3 is given to the 
> function call f().
> 
> 3) f() then "jumps" out of function def main(): to call function
> def f(whatever):, whose new value, 3, gets printed.
> 
> Is this what is going on? I find it difficult to get my head around this 
> one.
> Also: does Python go back to the function call main()'s position after 
> step 3)? How does that work? Again via def main():???


Your interpretation is correct. I guess what may trouble here is a question of order. main is defined before f, while its own definition uses f's definition. This is a bit weird, indeed, and does not help reading. But python doesn't mind. Instead, if ever main would actually be called/executed before f's definition, then you would get an error (try it).

denis


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