That helps for now. Thanks, Stefan
Am 15.09.2009 um 22:19 schrieb Nils Bruin: > > On Sep 15, 6:24 pm, Stefan Boettner <sboet...@tulane.edu> wrote: >> Hello, >> >> I'm trying to parse symbolic expressions, but got stuck very quickly. >> >> If I say: >> (x^2).operator() >> I get: >> <built-in function pow> >> >> If I say: >> pow >> I also get: >> <built-in function pow> >> >> But if I say: >> (x^2).operator()==pow >> I get: >> False >> >> How do I properly test if the topmost operation of an expression is a >> power, product, sum, whatever? > > The animal seems to be called: > > sage.symbolic.expression.operator.pow > > but if you don't want to bother figuring something like that out, you > can just cache it from a model equation: > > pow_as_a_symbolic_operator = (x^2).operator() > > and whenever you have a symbolic expression you expect is an > exponentiation, you can do > > expr.operator() == pow_as_a_symbolic_operator > > Mike Hansen has authored a file in the sage library "devel/sage/sage/ > symbolic/expression_conversions.py" that seems to make it easier to > traverse an expression tree. You may be able to save yourself some > work by inheriting from the classes he provides there and only > implement what needs to be done on the leaves. I ran into that file by > accident myself. It doesn't seem to be imported by default and I have > no experience using it. > > Be aware: expressions that do not have an operator can be a > SymbolicVariable or the method ".pyobject()" unpacks it: > > compare SR(x).pyobject() and SR(pi).pyobject(). > > I am not aware of other possibilities. > > Nils > > > --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
