Problems with get_systems and symbolic expressions

[Jean-Pierre Flori]

I'm using Sage 4.6.1.alpha2 with Pynac 0.2.1.

get_systems raises an error when called on a user created variable (but not on 'x'):

sage: get_systems('x+x')
[]
sage: get_systems('x*x')
[]
sage: a = var('a')
sage: get_systems('a+a')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

/home/jp/boulot/sage/sage-current/<ipython console> in <module>()

/home/jp/boulot/sage/sage-current/local/lib/python2.6/site-packages/sage/misc/citation.so in sage.misc.citation.get_systems (sage/misc/citation.c:873)()

/home/jp/boulot/sage/sage-current/local/lib/python/cProfile.pyc in runctx(statement, globals, locals, filename)
     47     try:
     48         try:
---> 49             prof = prof.runctx(statement, globals, locals)
     50         except SystemExit:
     51             pass

/home/jp/boulot/sage/sage-current/local/lib/python/cProfile.pyc in runctx(self, cmd, globals, locals)
    138         self.enable()
    139         try:
--> 140             exec cmd in globals, locals
    141         finally:
    142             self.disable()

/home/jp/boulot/sage/sage-current/<string> in <module>()

TypeError: unsupported operand type(s) for +: 'NoneType' and 'NoneType'
sage: get_systems('a*a')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

/home/jp/boulot/sage/sage-current/<ipython console> in <module>()

/home/jp/boulot/sage/sage-current/local/lib/python2.6/site-packages/sage/misc/citation.so in sage.misc.citation.get_systems (sage/misc/citation.c:873)()

/home/jp/boulot/sage/sage-current/local/lib/python/cProfile.pyc in runctx(statement, globals, locals, filename)
     47     try:
     48         try:
---> 49             prof = prof.runctx(statement, globals, locals)
     50         except SystemExit:
     51             pass

/home/jp/boulot/sage/sage-current/local/lib/python/cProfile.pyc in runctx(self, cmd, globals, locals)
    138         self.enable()
    139         try:
--> 140             exec cmd in globals, locals
    141         finally:
    142             self.disable()

/home/jp/boulot/sage/sage-current/<string> in <module>()

TypeError: unsupported operand type(s) for *: 'NoneType' and 'NoneType'

Similarly, get_systems('2a') and get_systems('a2') gives an error with None_Type

Moreover I get a segfault when calling get_systems on a power with symbolic expressions as base and exponent.

sage: from sage.misc.citation import get_systems
sage: get_systems('x**x')
[]
sage: a = var('a')
sage: get_systems('a**x')

Program received signal SIGSEGV, Segmentation fault.
0x00007fffd636b5c8 in __pyx_pf_4sage_8symbolic_10expression_10Expression___pow__ (__pyx_v_self=0x7ffff7dab0f0, __pyx_v_exp=0x42c03f8, __pyx_v_ignored=<value optimized out>) at sage/symbolic/expression.cpp:12008
12008         __pyx_t_1 = ((PyObject *)((struct __pyx_vtabstruct_4sage_8symbolic_10expression_Expression *)__pyx_v_base->__pyx_base.__pyx_base.__pyx_base.__pyx_base.__pyx_vtab)->coerce_in(__pyx_v_base, __pyx_v_exp)); if (unlikely(!__pyx_t_1)) {__pyx_filename = __pyx_f[1]; __pyx_lineno = 2447; __pyx_clineno = __LINE__; goto __pyx_L5_error;}

and :

sage: a = var('a')
sage: get_systems('x**a')

Program received signal SIGSEGV, Segmentation fault.
ptr (__pyx_v_self=<value optimized out>, __pyx_v_exp=0x7ffff7dab0f0, __pyx_v_ignored=<value optimized out>) at /home/jp/boulot/sage/sage-current/local//include/pynac/ptr.h:73
73              ptr(const ptr & other) throw() : p(other.p) { p->add_reference(); }

I'll have a deeper look at it later, but I have no idea of how get_systems work yet.

[Karl-Dieter Crisman]

I finally figured out why it works. For my own reference, or others who might have been similarly confused by this important but arcane subject. In some sense we're lucky that JP happened upon 'a', as many others weren't in this!

sage: get_systems('print locals()')
{'a': None, 'bad_res': None, 'systems_used': None, 'stats': None, 'bad_re': None, 'i': None, 'cmd': 'print locals()', 'system': None, 'filename': '/Users/karl-dietercrisman/.sage//temp/new_host_2.home/60265//tmp_2', 're': <module 're' from '/Applications/MathApps/sage/local/lib/python/re.pyc'>, 's': None, 'r': None, 'cProfile': <module 'cProfile' from '/Applications/MathApps/sage/local/lib/python/cProfile.pyc'>, 'pstats': <module 'pstats' from '/Applications/MathApps/sage/local/lib/python/pstats.pyc'>, 'strings': None}
[]

Yes, we wouldn't want to use these particular locals to exec the command.

And work the patch does, in a fair number of cases (using quite a few of the systems) I still tested. Good catch.