Sure, the output of free_symbols can be easily massaged with sorted. This is how I am working now. However the issue remains that a set is silently converted into a list with no guarantee of preserving the order. Working on a pull request...
On Fri, Jul 10, 2020, 20:49 Aaron Meurer <asmeu...@gmail.com> wrote: > If you use the free symbols as arguments, the question is, what order > should they be in? As you noted, they could go in any order. > > It is also not hard to do this manually. For example, > lambdify(sorted(expr.free_symbols, key=str), expr) will sort the > symbols in alphabetical order. > > Another option would be to require the symbols to be passed as keyword > arguments. As long as your symbol names are valid Python variable > names, lambdify will use them for the function arguments, so you can > pass them as keyword arguments. For example: > > >>> expr = x + 2*y > >>> f = lambdify(list(expr.free_symbols), expr) # list(free_symbols) could > give any order > >>> f(x=1, y=2) > 5 > > If you have a bunch of symbols, you can put them in a dictionary and > use f(**args). > > Aaron Meurer > > On Fri, Jul 10, 2020 at 10:47 AM Oscar Benjamin > <oscar.j.benja...@gmail.com> wrote: > > > > Hi Roberto, > > > > If you have something like > > expr = some_function(args) > > where some_function creates new symbols (not found in args) then > > ideally some_function should also return what the newly created > > symbols are or some other object that can tell you them: > > expr, syms = some_function(args) > > I think that attempting to guess what symbols should be used in any > > context by inspecting free symbols is not a good approach. > > > > Oscar > > > > On Fri, 10 Jul 2020 at 14:28, roberto franceschini > > <franceschini.robe...@gmail.com> wrote: > > > > > > The situation is the one in which I get a sympy expression out of a > function that ends in `return my_polynomial_inRn` and now I want to pass > this to another function (e.g. to make plots or whatever) without having to > know the names of the symbols involved, which is exactly what free_symbols > does for me in this instance. > > > Do you see another way around this? > > > > > > > > > On Fri, Jul 10, 2020 at 11:08 AM Oscar Benjamin < > oscar.j.benja...@gmail.com> wrote: > > >> > > >> Hi Roberto, > > >> > > >> I already answered this on SO: > > >> > https://stackoverflow.com/questions/62798213/keep-the-order-of-parameters-fixed-in-sympy-lambdify-from-free-symbols/62800716?noredirect=1#comment111075099_62800716 > > >> > > >> If you are using symarray to generate the symbols then you can get the > > >> list of symbols from the symarray directly and then pass those to > > >> lambdify. > > >> > > >> I can't think of any situation where it would be a good idea to use > > >> free_symbols to get the arguments to lambdify. > > >> > > >> Oscar > > >> > > >> On Fri, 10 Jul 2020 at 08:10, roberto franceschini > > >> <franceschini.robe...@gmail.com> wrote: > > >> > > > >> > Hello, I have opened an issue for the input of lambdify. If you > want to disallow sets as inputs I think it is fair. However, It would be > nice to have that free_symbol can be given directly as input for lambdify, > is that possible? should I use something else than free_symbols for this > purpose? > > >> > > > >> > On Thu, Jul 9, 2020 at 9:55 PM Aaron Meurer <asmeu...@gmail.com> > wrote: > > >> >> > > >> >> Can you open an issue in the issue tracker for this? I agree that > sets > > >> >> should not be allowed. > > >> >> > > >> >> Aaron Meurer > > >> >> > > >> >> On Thu, Jul 9, 2020 at 3:08 AM Roberto < > franceschini.robe...@gmail.com> wrote: > > >> >> > > > >> >> > I have seen that lambdify wants a list for the arguments to be > treated as symbols. This list can be also give as a python set, e.g. {x,y,z > }, which is exactly what would be returned by a .free_symbol property. If > lambdify is feed a set like that of the output of .free_symbol it may > change their order in the conversion from set to list. This is done > silently and may cause major disfunction in the use of the lamdified > function because you think x is x, but is y instead and so on. > > >> >> > I would like to ask developers to check for the type of the > lambdify list of arguments and throw a warning to flag that a set is being > converted and that the ordering is not guaranteed. > > >> >> > Given that .free_symbols returns a set, not a list, this is very > common pitfall in my opinion and must be prevented. > > >> >> > > > >> >> > -- > > >> >> > 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 sympy+unsubscr...@googlegroups.com. > > >> >> > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/c1517b79-490b-4a1b-b526-3e3842b55fbco%40googlegroups.com > . > > >> >> > > >> >> -- > > >> >> 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 sympy+unsubscr...@googlegroups.com. > > >> >> To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CAKgW%3D6KuqnjJHTObyDxK0tvaF_Frxzd-MfyQSY94v-oTUWyNAg%40mail.gmail.com > . > > >> > > > >> > -- > > >> > 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 sympy+unsubscr...@googlegroups.com. > > >> > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CAJxM9JqSoqQQkYH9UUXGyXNqRtY9VHJxKByc8Fv8%2BPaqFudP6w%40mail.gmail.com > . > > >> > > >> -- > > >> 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 sympy+unsubscr...@googlegroups.com. > > >> To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CAHVvXxSsngVE_X-aBRYWER5sESZW-e-EnjwWcfGAhM%3D%2Beq97zQ%40mail.gmail.com > . > > > > > > -- > > > 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 sympy+unsubscr...@googlegroups.com. > > > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CAJxM9Jpza%3DgRk9%3DZ2_thBS4xN_dkjCaB5PTMcz1hj8wHG_R90g%40mail.gmail.com > . > > > > -- > > 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 sympy+unsubscr...@googlegroups.com. > > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CAHVvXxQCPtBmmcjoVKv0jqYFqezsUQ5zWox_Q16x72ygng37Xg%40mail.gmail.com > . > > -- > 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 sympy+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/CAKgW%3D6KepRmoA-JT5KzTB9EFx3dhnkPLyZoTqJrhsi5w%2BtWT9g%40mail.gmail.com > . > -- You received this message because you are subscribed to the Google Groups "sympy" group. 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