On Aug 31, 2012, at 5:12 AM, Juha Jeronen <[email protected]> wrote:
> On 31.08.2012 13:03, Chris Smith wrote: >> On Fri, Aug 31, 2012 at 3:30 PM, Juha Jeronen <[email protected]> wrote: >>> Hi all (again), >>> >>> And here's a fixed version. The code I just posted returned some nonsensical >>> results, because it didn't filter out modules and classes. >> Another way to maybe approach this problem (getting a non-clashing >> form of an expression sympified) is this: >> >> * the user must know what functions they are using: they/you give a >> list of these and this list must agree with the representation of that >> function's name in sympy >> * they give an expressions >> * let python parse this (I don't recall which does that now -- there's >> some module for parsing python code character by character) and when >> it identifies a variable either 1) it is a function that has already >> been identified or it is intended as a symbol and 2a) sympy agrees or >> 2b) sympy disagrees and wants to make it a class or anything other >> than a symbol. The tokenize module will split a string of valid python code into its tokens, which you can then search for names. Or if you don't need 2.5 support, you can use the ast module. If you want, you could then sympify the name and see if you get a Symbol or not (caching the results). >> * in case of 2b the user's symbol must be de-clashed, by appending >> underscores until the clash goes away; this symbol replaces what the >> user chose >> * the modified input function is returned. > > Thanks for the idea! I hadn't considered this approach. > > This would be pretty easy to do the other way around: undefined symbols are > not allowed in my particular use case, and the code already builds a list of > user-defined symbols. Anything not explicitly defined is intended to be taken > from the library... > > > Related to which, I have one more question. In 0.6.x sympify() used to add an > undefined_Function attribute to unknown functions in the expression: > > import sympy as sy > s = sy.sympify("a*f(x) + b + c*x") > L = list(s.atoms(sy.Function)) > f = L[0] > hasattr(f, "undefined_Function") > => True > > but 0.7.x no longer does this. > > Is it possible to dynamically detect in the new version whether a function > object is evaluatable or not, and user-defined or not? At least I couldn't > find anything obvious in the attributes... In 0.7.2 you will be able to check if it is a subclass of UndefinedFunction. I don't know if that works in 0.7.1 or what would be a work around if not. Aaron Meurer > > What I'd like to do with this is to check that all function references in a > user-given expression refer to existing library functions only. I could > utilize the get-reserved-symbols-by-dir(sympy) hack and check the object > type, but that's hardly an elegant solution. > > > -J > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
