There is no coercion from string and Integer to a common structure. That
should be obvious, but we can also check it explicitly:
sage: cm = get_coercion_model()
sage: cm.explain('i', ZZ(0), operator.eq)
Left operand is not Sage element, will try _sage_.
Unknown result parent.
Hence the comparison is by memory position, which is essentially random
(and very much platform-dependent).
On Tuesday, July 22, 2014 12:57:13 PM UTC-4, Clemens Heuberger wrote:
>
> Can anyone help me understanding the following behaviour:
>
> A doctest (0 < 'I'; see below) passes when called directly and fails when
> called
> via a Makefile, reproduced under sage 6.3.beta6, 6.2, 5.10 (running Linux
> Mint).
>
> As pointed out in
>
> https://groups.google.com/d/topic/sage-support/KNSzU0JpZgQ/discussion ,
> comparison between str and Integer falls back to comparison between the
> types.
>
> Does that simply mean that cmp(str, sage.rings.integer.Integer) is random?
>
> Is the behaviour reproducible on other systems?
>
> This problem turned up when trying to find out why Volker Braun has
> problems
> with doctests in #16580 which I cannot reproduce. There, we need to
> somehow sort
> transitions in a finite state machine; the order itself does not really
> matter,
> but for doctests, it is important to always have the same order.
>
>
> $ cat test-cmp.sage
> """
> ::
> sage: a = 0
> sage: b = 'I'
> sage: type(a)
> <type 'sage.rings.integer.Integer'>
> sage: type(b)
> <type 'str'>
> sage: cmp(type(a), type(b))
> -1
> sage: a < b
> True
> """
> $ cat Makefile
>
> doctest:
> sage -t test-cmp.sage
>
> $ LANG=C make
> sage -t test-cmp.sage
> Running doctests with ID 2014-07-22-18-46-45-0e337b53.
> Doctesting 1 file.
> sage -t test-cmp.sage
> **********************************************************************
> File "test-cmp.sage", line 9, in test-cmp
> Failed example:
> cmp(type(a), type(b))
> Expected:
> -1
> Got:
> 1
> **********************************************************************
> File "test-cmp.sage", line 11, in test-cmp
> Failed example:
> a < b
> Expected:
> True
> Got:
> False
> **********************************************************************
> 1 item had failures:
> 2 of 7 in test-cmp
> [6 tests, 2 failures, 0.00 s]
> ----------------------------------------------------------------------
> sage -t test-cmp.sage # 2 doctests failed
> ----------------------------------------------------------------------
> Total time for all tests: 0.0 seconds
> cpu time: 0.0 seconds
> cumulative wall time: 0.0 seconds
> make: *** [doctest] Error 1
>
> $ sage -t test-cmp.sage
> Running doctests with ID 2014-07-22-18-47-10-577db6a3.
> Doctesting 1 file.
> sage -t test-cmp.sage
> [6 tests, 0.00 s]
> ----------------------------------------------------------------------
> All tests passed!
> ----------------------------------------------------------------------
> Total time for all tests: 0.0 seconds
> cpu time: 0.0 seconds
> cumulative wall time: 0.0 seconds
>
>
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