[Python-Dev] PEP 288: Generator Attributes

Jack Jansen Jack.Jansen@cwi.nl
Fri, 22 Nov 2002 11:35:28 +0100

On Friday, Nov 22, 2002, at 09:46 Europe/Amsterdam, Raymond Hettinger 
> def outputCaps(logfile):
>     while True:
>         line = __self__.data
>         logfile.write(line.upper)
>         yield None
> outputCaps.data = ""      # optional attribute initialization
> g = outputCaps(open('logfil.txt','w'))
> for line in open('myfile.txt'):
>     g.data = line
>     g.next()

I don't like it, there's "Magic! Magic!" written all over it. 
Generators have always given me that feeling (you start reading them as 
a function, then 20 lines down you meet a "yield" and suddenly realize 
you have to start reading at the top again, keeping in mind that this 
is a persistent stack frame), but with the __self__ plus the fact that 
you local variables may not be what they appear to be makes it hairy. 
You basically cannot understand the code without knowing the code of 
the caller. There's also absolutely no way to get encapsulation. So 
count me in for a -1.

Generators have to me always felt more "class-instance-like" than 
"function-like", and I guess this just goes to show it.
- Jack Jansen        <Jack.Jansen@oratrix.com>        
http://www.cwi.nl/~jack -
- If I can't dance I don't want to be part of your revolution -- Emma 
Goldman -