0-length lazy tuples

[Alex Martelli]

VERY interesting concept!

I'm a bit perplexed about the implementation of 0-length lazy tuples -- shouldn't the tests in class LazyTuple be
self._length >= 0
rather than
self._length > 0
...?
A zero-length tuple seems a natural thing, lazy or otherwise, and indeed non-terminating lazy tuples are encoded with _length<0, but the tests seem to imply that a _length that is ==0 has strange properties; e.g. the tuple appears to be non-terminating, if looping over it with a for the function is still called once, etc, e.g.:
>>> import functional
>>> lz=functional.LazyTuple(length=0)
>>> for i in lz:
...     print i
...    
Traceback (innermost last):
  File "<interactive input>", line 1, in ?
  File "functional.py", line 538, in __getitem__
    val = self._itemFunc(i, self)
TypeError: call of non-function (type None)
>>>

Fixing the tests to >= 0, e.g. in LazyTuple:
    def isTerminating(self):
        """
        Return 0 if this is a finite tuple, 1 if it is infinitely long.
        """
        return self._length >= 0

    def __getitem__(self, i):
        if self._length >= 0 and i >= self._length:
            raise IndexError, i

(etc) does seem to fix this correctly, i.e.:

>>> lz=functional.LazyTuple(length=0)
>>> for i in lz:
...     print i
...    
>>>

Am I missing something...?

Thanks!

Alex

[Bryn Keller]

Thanks, I'm glad you like it!

You're absolutely right, there's no reason not to support 0 length lazy tuples, it's an
oversight I'll remedy in the next release.

Thanks for your help!

Bryn