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.
>> >
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