Hello all,
I was a bit surprised to find out just how lazy LazyFamily is:
sage: f = Family(Zmod(3), lambda i: 2*i) # This will be lazy by default
sage: f[2] # I think this should be 1
4
sage: f['spam'] # I think this should fail
'spamspam'
Compare with:
sage: f = Family([i for i in Zmod(3)], lambda i: 2*i)
sage: f[2]
1
sage: f['spam']
KeyError: 'spam'
I expected that the __getitem__ method for lazy family would
1) Check that the value given is (or can be coerced to) a key, and
2) If a coercion is necessary, call the function on the coerced item.
But I guess that not everyone agrees since one of the tests in LazyFamily is
sage: f = LazyFamily([3,4,7], lambda i: 2*i)
sage: f[5]
10
Perhaps there are arguments about pythonic code and the value of
duck-typing that I'm not appreciating here. Or maybe the issue is
performance. But can someone say a few words about the rationale for
this decision?
On a related note, the following *really* looks like a bug to me:
sage: f = Family(Zmod(3), lambda i: 2*i, lazy=False)
sage: f
Lazy family (<lambda>(i))_{i in Ring of integers modulo 3}
Should we really just silently ignore the intent here, or should
Family(S, f, lazy=False) always return Family([i for i in S], f)
(I guess the default for lazy should then be made 'None' so that 'True',
'False' and 'None' could all have different behaviors.)
Thanks,
Jason
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