[Python-Dev] re: for in dict (user expectation poll)

[Greg Wilson]

> > > > On Mon, 5 Feb 2001, Greg Wilson wrote:
> > > > Based on my very-informal survey, if:
> > > >     for i in someList:
> > > > works, then many people will assume that:
> > > >     for i in someDict:
> > > > will also work, and yield values.

> > > Ka-Ping Yee:
> > > ...the latter is ambiguous (keys or values?)...

> > Greg Wilson

> > The latter is exactly as ambiguous as the former...  I think this
> > is a case where your (intimate) familiarity with the way Python
> > works now is preventing you from getting into newbie headspace...

> Ka-Ping Yee:
> No, i don't think so.  It seems quite possible to argue from first
> principles that if you ask to iterate over things "in" a sequence,
> you clearly want the items in the sequence, not their integer indices.

Greg Wilson:
Well, arguing from first principles, Aristotle was able to demonstrate that
heavy objects fall faster than light ones :-).  I'm basing my claim on the kind
of errors students in my course make.  Even after being shown half-a-dozen
examples of Python for loops, many of them write:

    for i in someSequence:
        print someSequence[i]

in their first exercise.

Thanks,
Greg