#14583: Permutation('()') and Permutation(''), each in its own way, fail to
return
the identity in S_0
----------------------------------+-----------------------------------------
Reporter: darij | Owner: sage-combinat
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.10
Component: combinatorics | Resolution:
Keywords: combinat | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Darij Grinberg | Merged in:
Dependencies: | Stopgaps:
----------------------------------+-----------------------------------------
Changes (by {'newvalue': u'Darij Grinberg', 'oldvalue': ''}):
* cc: tscrim, nthiery (added)
* status: new => needs_review
* author: => Darij Grinberg
Old description:
> I brought this up in #8392 but was told to post it as a new ticket.
>
> {{{
> sage: Permutation([]) # This is be the identity permutation in S_0.
> []
> sage: Permutation([]).cycle_string() # OK.
> '()'
> sage: Permutation('()') # This should give the S_0 identity back --
> but it doesn't.
> [1]
> sage: Permutation('') # Does this maybe? No.
> ---------------------------------------------------------------------------
> ValueError Traceback (most recent call
> last)
> <ipython-input-29-3df27d9d4d7a> in <module>()
> ----> 1 Permutation('')
>
> /home/darij/sage-5.10.beta2/local/lib/python2.7/site-
> packages/sage/combinat/permutation.pyc in Permutation(l, check_input)
> 430 cycle_list = []
> 431 for c in cycles:
> --> 432 cycle_list.append(map(int, c.split(",")))
> 433
> 434 return from_cycles(max([max(c) for c in cycle_list]),
> cycle_list)
>
> ValueError: invalid literal for int() with base 10: ''
> sage: Permutation(()) # What about this?
> [1]
>
> }}}
>
> A corner case it is, but I think it should be done right...
New description:
I brought this up in #8392 but was told to post it as a new ticket.
{{{
sage: Permutation([]) # This is be the identity permutation in S_0.
[]
sage: Permutation([]).cycle_string() # OK.
'()'
sage: Permutation('()') # This should give the S_0 identity back -- but
it doesn't.
[1]
sage: Permutation('') # Does this maybe? No.
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
<ipython-input-29-3df27d9d4d7a> in <module>()
----> 1 Permutation('')
/home/darij/sage-5.10.beta2/local/lib/python2.7/site-
packages/sage/combinat/permutation.pyc in Permutation(l, check_input)
430 cycle_list = []
431 for c in cycles:
--> 432 cycle_list.append(map(int, c.split(",")))
433
434 return from_cycles(max([max(c) for c in cycle_list]),
cycle_list)
ValueError: invalid literal for int() with base 10: ''
sage: Permutation(()) # What about this?
[1]
}}}
A corner case it is, but I think it should be done right...
This is now fixed in the attached patch.
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14583#comment:3>
Sage <http://www.sagemath.org>
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