Range Operation pre-PEP

[Douglas Alan]

Ben Hutchings <ben.hutchings at roundpoint.com> writes:

> Douglas Alan <nessus at mit.edu> writes:

> > Speaking of creeping-featurism, how come we have list comprehension,
> > but not tuple comprehension?  Seems inconsistent to me.

> A list contains a variable number of homogeneous values, e.g. the
> lines of a file.  Lists are like arrays in other languages.  A tuple
> contains a fixed number of heterogeneous values where each element
> has a distinct meaning e.g. (year, month, day) for a date.

I think you have some other language in mind, rather than Python.  In
Python, the only semantic difference between a list and a tuple is
that a tuple is immutable.

> Tuples are like data structures or product types in other languages,
> except that their types and fields are nameless.  Comprehensions
> work with a variable number of homogeneous values, so they produce
> lists.

filter() on a tuple returns a tuple.  The length of the tuple cannot
be known in advance.  map(), on the other hand, always returns a list.
But map can take multiple sequence arguments, so it wouldn't always be
obvious to know which type of sequence to duplicate.  I suppose the
same is true for comprehension.  But, it seems to me that Python could
allow

   (x*2 for x in t)

to make a tuple as easily as it allows

   [x*2 for x in l]

to make a list.

|>oug