You'll need to override __neg__. Aaron Meurer
On Oct 13, 2013, at 3:35 AM, Ben Lucato <[email protected]> wrote: Thanks for your help - I've been doing a bit of work on this. Another thing: x = noevalMul(2, 5) y = -x The type of y is a sympy.core.Integer - i.e. the assignment of y to -x evaluates x in the process. I'm not sure what behaviour I need to override for this. BTW what I did with the printing is subclass LatexPrinter so I keep a lot of the already-done work. On 13 October 2013 03:27, Aaron Meurer <[email protected]> wrote: > Yes, for general objects, you have to override __new__. In general, > you just need to define a __new__ that looks like the one above, > except without the "if evaluate" branch (if you don't care about > noncommutatives you can skip that bit too). Basically > > - sympify the arguments. _sympify is used so that strings aren't supported. > - Create a new Expr of the given class. If your class doesn't subclass > from Expr, use Basic instead. This contains some vital logic such as > setting up the hash, so don't skip it. > - Return that object. > > By the way, for your Add and Mul, in your flatten, you may want to > override flatten to actually flatten things, so that NoevalAdd(x, y, > NoevalAdd(z, t)) is the same as NoevalAdd(x, y, z, t). Otherwise, > there's little point in overriding flatten instead of __new__ there. > > Aaron Meurer > > > On Fri, Oct 11, 2013 at 8:21 AM, Ben Lucato <[email protected]> wrote: > > This is awesome!!! Your simple fix with overriding flatten() works > > perfectly. My last question is -- how do you do the same thing with Pow? > It > > is subclassed differently to Add, Mul (which both subclass "AssocOp"). > > I have taken a look at the source code (go me!!!) - it seems that in this > > case, because Pow is defined like this: > > > > "def __new__(cls, b, e, evaluate=True): > > b = _sympify(b) e = _sympify(e) if evaluate: if e is S.Zero: return S.One > > elif e is S.One: return b else: obj = b._eval_power(e) if obj is not > None: > > return obj obj = Expr.__new__(cls, b, e) obj.is_commutative = > > (b.is_commutative and e.is_commutative) return obj" > > > > > > So it seems a change to __new__ is necessary, right? It looks like > > evaluate=False is not even supported for Pow - am I right? (just a noob > > asking questions) > > > > Thanks!! > > > > -- > > You received this message because you are subscribed to the Google Groups > > "sympy" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to [email protected]. > > To post to this group, send email to [email protected]. > > Visit this group at http://groups.google.com/group/sympy. > > For more options, visit https://groups.google.com/groups/opt_out. > > -- > You received this message because you are subscribed to a topic in the > Google Groups "sympy" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/sympy/zilEXwN26so/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy. > For more options, visit https://groups.google.com/groups/opt_out. > -- Ben Lucato ---------------------------------------------------------------------------------- Phone: +61 400 159 632 | Email: [email protected] -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. For more options, visit https://groups.google.com/groups/opt_out.
