#15567: Fix Alphabet and improvements to Family
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Reporter: tscrim | Owner: sage-combinat
Type: defect | Status: needs_work
Priority: major | Milestone: sage-6.1
Component: combinatorics | Resolution:
Keywords: alphabet | Merged in:
Authors: Travis Scrimshaw | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
public/combinat/words/fix_alphabet | b3396dd62e96a08621cf08a6b2573c59a664adac
Dependencies: | Stopgaps:
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Comment (by tscrim):
Replying to [comment:2 ncohen]:
> Hello !
>
> I don't know how this "names" argument is used at all, but its current
behaviour is the following :
>
> {{{
> sage: build_alphabet(oo,'x')[4]
> 'x4'
> sage: build_alphabet(range(40),'x')[4]
> 4
> }}}
>
> Which is not very consistent.
This is also inconsistent input types (one is a "number", the other is a
set). However the other could raise an error as invalid input as opposed
to being silently ignored.
> While playing with it I found something else which totally scares me :
>
> {{{
> sage: build_alphabet(oo,'x')
> Lazy family (x(i))_{i in Non negative integers}
> sage: build_alphabet(oo,'x')[:4]
> 'xslice(None, 4, None)'
> sage: print list(build_alphabet(oo,'x')[:4])
> ['x', 's', 'l', 'i', 'c', 'e', '(', 'N', 'o', 'n', 'e', ',', ' ', '4',
',', ' ', 'N', 'o', 'n', 'e', ')']
> }}}
>
> While I expected to get the list of the first 4 elements. And I really
do not know what to make with that `O_o`
This is an issue with `Family` in that it is directly passing a string
representation of the input of `__getitem__()` without any safety checks
(for speed). It's outside the scope of what I want to do in this ticket
and has a landmine of "you've picked a specific ordering of the indices
that may not be canonical".
> Anyway, I think that the `build_alphabet` function could use a "INPUT"
section explaining its parameters, and in particular the "names" field.
Which, in the context of `build_alphabet(oo,'x')` would be better renamed
to "prefix", as it adds this string to all members of the family.
I'll add it. Since "names" not (really) used anywhere else, I'll change
it.
> About the modifications to `Family` :
> * would it be possible to add to the documentation of "hidden_keys" an
explanation of what exactly it does ? Does it mean that the hidden keys
are "skipped", i.e. removed from "indices" ?
It means they are valid keys (indices) of the Family that are hidden.
> * the explanation of what `hidden_function` is isn't very clear either
`O_o`
Then neither should be the one for `function` (or does it make sense if I
change the `a` to a `the` in `hidden_function`?).
> The fact that the "name" argument does nothing for finite lists should
be made clear I guess. I mean, what is it useful for exactly?
So lazy familys display nicely (espically when using lambda functions).
--
Ticket URL: <http://trac.sagemath.org/ticket/15567#comment:3>
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