I was able to write a LambdaPrinter that does what I want for the time
being:
class NonRelationalOpPrinter(lambdarepr.LambdaPrinter):
'''
>>> from structures import symbolic
>>> for op in ['Eq', 'Ne', 'Gt', 'Lt', 'Ge', 'Le']:
...
sympy.sympify((symbolic.NonRelationalOpPrinter().doprint(sympy.sympify('%s(%s(a,
b), c)' % (op, op)))))
(a == b) == c
(a != b) != c
(a > b) > c
(a < b) < c
(a >= b) >= c
(a <= b) <= c
'''
def _printRelation(self, expr, name):
return '%s(%s)' % (name, ", ".join(map(self._print, expr.args)))
def _print_Equality(self, expr):
return self._printRelation(expr, 'Equality')
def _print_Unequality(self, expr):
return self._printRelation(expr, 'Unequality')
def _print_GreaterThan(self, expr):
return self._printRelation(expr, 'GreaterThan')
def _print_LessThan(self, expr):
return self._printRelation(expr, 'LessThan')
def _print_StrictGreaterThan(self, expr):
return self._printRelation(expr, 'StrictGreaterThan')
def _print_StrictLessThan(self, expr):
return self._printRelation(expr, 'StrictLessThan')
On Friday, May 29, 2015 at 4:31:59 AM UTC-5, Robert wrote:
>
> Hello,
>
> Thanks for the help previously. I've run into a different issue with
> regards to Eq.
>
> Sympify will automatically convert Eq into ==
> >>> sympy.sympify('Eq(a, b)')
> a == b
>
> which if you sympify again will have the behavior you described originally.
> >>> sympy.sympify(str(sympy.sympify('Eq(a, b)')))
> False
>
> Do you know of any way to stop the converion of Eq to ==?
>
> Thanks,
> Rob
>
>
>
> On Friday, April 27, 2012 at 5:29:53 PM UTC-5, Aaron Meurer wrote:
>>
>> Equal is not anything. You've just created an undefined function
>> called Equal (Function('Equal')) with that sympify command.
>>
>> What you are probably looking for is Eq() (or Equality()). This
>> creates a symbolic equality. You can manipulate different sides of
>> the equation using Eq.lhs and Eq.rhs, like
>>
>> In [496]: Eq(x, y)
>> Out[496]: x = y
>>
>> In [497]: Eq(x, y).lhs
>> Out[497]: x
>>
>> In [498]: Eq(x, y).rhs
>> Out[498]: y
>>
>> Eq() will reduce to True when or False when it can see that the
>> expressions are always equal or unequal:
>>
>> In [504]: Eq(x, y).subs({x: 1, y: 1})
>> Out[504]: True
>>
>> In [505]: Eq(x, y).subs({x: 1, y: 2})
>> Out[505]: False
>>
>> == is a lot different. This is used to exactly compare expressions.
>> a == b will be a boolean, True if a and be are exactly equal and False
>> otherwise. I say "exactly" equal because == does structural
>> comparison, not mathematical comparison. So we have
>>
>> In [499]: x*(y + z) == x*y + x*z
>> Out[499]: False
>>
>> In [500]: x*(y + z) == x*(y + z)
>> Out[500]: True
>>
>> If you want to do a mathematical comparison, the best way is to
>> subtract one expression from the other and pass it to simplify(), and
>> see if it goes to 0. For example:
>>
>> In [501]: a = x*(y + z)
>>
>> In [502]: b = x*y + x*z
>>
>> In [503]: simplify(a - b)
>> Out[503]: 0
>>
>> See http://docs.sympy.org/dev/gotchas.html#equals-signs for more
>> discussion on this.
>>
>> Aaron Meurer
>>
>> On Fri, Apr 27, 2012 at 4:16 PM, Robert <[email protected]> wrote:
>> > Hello,
>> >
>> > I have a question about == and Equal in sympy.
>> >
>> > Their behavior is strange to me.
>> >
>> > In [108]: expr = sympy.simplify('Equal(A,B)')
>> > In [111]: expr.subs(dict(A=1, B=1))
>> > Equal(1, 1)
>> >
>> > In [112]: expr = sympy.simplify('A==B')
>> > In [113]: expr
>> > False
>> >
>> > In [115]: A = sympy.Symbol('A')
>> > In [116]: B = sympy.Symbol('B')
>> >
>> > In [117]: A==B
>> > False
>> >
>> > In [118]: sympy.__version__
>> > '0.7.1'
>> >
>> > --
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>> >
>>
>
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