tuples, index method, Python's design

[Carsten Haese]

On Tue, 2007-04-10 at 13:21 +0000, Antoon Pardon wrote:
> >  But if you are so eager to rewrite, how about the following:
> > 
> > I am using the struct module to get binary data from a file.
> > Sometimes I want to skip until I find a particular binary
> > number. Somewhat simplified it looks like this:
> > 
> > 
> > class Itemfile:
> >   def __init__(self, fn):
> >     self.fl = open(fn)
> >     self.ix = 80
> > 
> >   def nextitem(self):
> >     if self.ix == 80:
> >       self.buf = struct.unpack("80i", self.fl.read(320))
> >       self.ix = 0
> >     result = self.buf[self.ix]
> >     self.ix += 1
> >     return result
> > 
> >   def skipuntil(self, val):
> >     done = False
> >     while not done:
> >       try:
> >         self.ix = self.buf.index(val, self.ix)
> > 	done = True
> >       except ValueError:
> >         self.ix = 0
> > 	self.buf = struct.unpack("80i", self.fl.read(320))
> > 
> > 
> > Now I'm sure you can rewrite this without the need of tuple.index.
> > It just seems odd that I have to go through extra hoops here to
> > get the effect of tuple.index because struct.unpack returns its result
> > in a tuple and a tuple doesn't provide index.

Your data is an array. Choosing a data structure that doesn't fit your
data is always going to cause pain. Instead of using struct.unpack, you
should use array.array, and voila!, you get an index method.

-Carsten