[Python-Dev] re: syntax - "Aren't tuples redundant?"

[Guido van Rossum]

> > > 4. "Aren't tuples redundant?"
> 
> > To my mind, the "can act as dictionary key" argument is a red
> > herring. Tuples and lists may technically be almost the same
> > thing, but I find I hardly ever need to ponder whether I should
> > use a tuple or a list. Tuples are structures and lists are
> > containers.
> 
> They're not structures the way a C programmer thinks of a struct or a pascal
> programmer thinks of a record.

That doesn't matter; I'd like to assume that we want to teach students
who don't already have a preconceived notion of a Pascal record or C
struct.

> Do you have a better way of justifying their existence to novices who
> haven't reached the zen?  It's a nontrivial pedagogical problem in my
> experience as well. (yes, this is a better topic for edu-sig than for
> python-dev).

I have a feeling that introducing optional static typing would help
here, because it clarifies the concept.  For example, these two have
the same type, [int]: (the length is part of the value)

  [3, 100]
  [5, 6, 7]

On the other hand, these two have different types:

  (3, 100)	   	# (int, int)
  (5, 6, 7)	   	# (int, int, int)

If we start mixing types, we may get

  [3, "wow"]		# [any]; or perhaps [int|str]
  (3, "wow")		# (int, str)

We can then explain that we might have informal names for the parts,
and we can use these as local variable names.  This is borrowed
 from ABC, which did at least *some* user testing on issues like this:

  count, value = t
  t = count, value

(ABC used a different assignment syntax; it would be:

  PUT t IN count, value
  PUT count, value IN t

I am still friends with the librarian who was taught ABC as a guinea
pig.)

However, ABC was a statically typed language in the sense of Haskell:
there were no declarations but the types were inferenced from
initializations and operators.  Maybe that *does* make a difference.
Also, its tuples were completely unlike sequences: they didn't have
indexing or slicing.  There were no tuples of lengths 1 or 0.

--Guido van Rossum (home page: http://www.python.org/~guido/)