Hi Danny, Thanks a lot for the advice. I will put that in practice.
The blasphemous example is on page 227 of the second edition, under Mapping Functions Over Sequences. Cheers Bernard On 5/11/05, Danny Yoo <[EMAIL PROTECTED]> wrote: > > > I have to confess that I already use map(), or should I say abuse, for > > this, although it is the first time I consider using lambdas. Up until > > now I always used map() to perform a looped call on a function that > > would change the attribute value, as shown in Mark Lutz & David Ascher's > > Learning Python: > > > > # Perform attribute value change on a single instance > > def iterateInstances( oInstance ): > > oInstance.value = myValue > > > > # Loop over list of instances > > map( iterateInstances, aListOfInstances ) > > What!!! Seriously? I'm making a style judgement here, so perhaps I could > be wrong, but I think that's terrible that Learning Python has such an > example. If you have a page number, I'll look it up and then write a > complaint. *grin* > > The major problem here is that both map() and list comprehensions are > really meant to be used because they generate a list of return values. > > If we use a map() or list comprehensions, such as: > > map(lambda x: x^2, [1, 2, 3]) > > [x^2 for x in [1, 2, 3]] > > then we're really saying something like this: > > [1, 2, 3] > | | | > | | | map() > | | | > V V V > [1, 4, 9] > > where map() produces a list of values. > > If we're using map() just because it evaluates something on every element > on a list, then, to make the intent more clear, we really should either > use something like a foreach() function instead of map(): > > ###### > def foreach(function, l): > """Apply some function on every element in l. Does not accumulate > return values.""" > for x in l: > function(l) > ###### > > If we use something like foreach(0, then this makes it clear that we > really don't care about return values at all. > > I should add that I'm arguing for style here. Things do work pefectly > well with map() too --- the computer doesn't care that it's throwing > return values away --- but we should do our best to document intent in our > programs. > > Best of wishes! > > _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
