Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[roberto franceschini]

FYI
https://github.com/sympy/sympy/pull/19792

On Fri, Jul 17, 2020 at 3:27 PM roberto franceschini <
franceschini.robe...@gmail.com> wrote:

> Thanks, I think this is why lambdify should not accept anything that
> hasn't a fixed ordering - this part of lambdify was coded too lighthearted
> in my opinion. So I am working on a pull request but I would like to have
> some discussion on what to do to make lambdify better in this sense.
>
> At this time lambdify can give unpredictable outcome, because it accepts
> set and uses enumerate. That's a bug to correct in my opinion. Rightnow I
> have a work in progress for a pull request. I have added simple code to
> warn about the use of set as input, but I would like to give a more general
> solution to this problem. This, for instance, should warn about other types
> of inputs that have not fixed order.
>
> I am tempted to modify by adding specific type checks to warn when used
> with set, dict, but let list, OrderedDicts, sequence go through as usual.
> In all cases I'd let the function do the same as it has been doing so far.
>
> Any comment?
>
> On Fri, Jul 17, 2020 at 2:52 PM Jared Claypoole 
> wrote:
>
>> Hi Roberto,
>>
>> It looks like you're expecting python sets to do something they're not
>> intended to do.  From the docs
>> ,
>> "A set object is an unordered collection".  Of course when you iterate over
>> all the elements they have to come out in some order, but that's an
>> implementation choice.  Elements are not even guaranteed to be returned in
>> the same order each time!  (Though probably they will be.)
>>
>> I can see how one might expect enumerate to only make sense for
>> containers which have some guaranteed order, but that's not the way it's
>> been designed to work.  It simply iterates over any iterable and gives you
>> an index counting how many elements have been seen so far*.
>>
>> In general if you want a container with guaranteed ordering, you probably
>> want to use a list or a tuple, or even a dict (which has had ordering
>> guarantees since python 3.7).  You might also be interested in the answers
>> to this stackoverflow question on implementing an OrderedSet
>> in python.
>>
>>
>> * Actually one is able to change the starting value of this index from 0
>> to something else, but that's somewhat beside the point.
>>
>> On Thursday, July 16, 2020 at 5:34:27 PM UTC-4, Roberto wrote:
>>>
>>> I am starting to wonder why python is so loose on this. I say "python"
>>> because the issue appears for enumerate as well. How can I enumerate a set?
>>> Still I am allowed to enumerate a set without receiving any warning. Look
>>> at this for instance
>>>
>>> set(["a","b"])==set(["b","a"])
>>> list(enumerate(set(["a","b"])))
>>> list(enumerate(set(["b","a"])))
>>> import sympy as sp
>>> _a, _b = sp.symbols('a b')
>>> set([_a,_b])==set([_b,_a])
>>> list(enumerate(set([_a,_b])))
>>> list(enumerate(set([_b,_a])))
>>>
>>>
>>> Funny enough, moving this code from one notebook to another may change
>>> the order in which the sets are ordered. In all cases they are ordered in
>>> the same way within the same notebook, but you and I running the same code
>>> may get different outcomes!
>>> I do not know if this is special with sets of sympy symbols, but I would
>>> have said that deep down enumerate should throw a warning when you try to
>>> enumerate a set.
>>>
>>>
>>>
>>> On Thursday, July 9, 2020 at 9:55:15 PM UTC+2, Aaron Meurer 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  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 sy...@googlegroups.com.
 > To view this discussion on the web visit
 https://groups.google.com/d/msgid/sympy/c1517b79-490b-4a1b-b526-3e3842b55fbco%40googlegroups.co

Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[roberto franceschini]

Thanks, I think this is why lambdify should not accept anything that hasn't
a fixed ordering - this part of lambdify was coded too lighthearted in my
opinion. So I am working on a pull request but I would like to have some
discussion on what to do to make lambdify better in this sense.

At this time lambdify can give unpredictable outcome, because it accepts
set and uses enumerate. That's a bug to correct in my opinion. Rightnow I
have a work in progress for a pull request. I have added simple code to
warn about the use of set as input, but I would like to give a more general
solution to this problem. This, for instance, should warn about other types
of inputs that have not fixed order.

I am tempted to modify by adding specific type checks to warn when used
with set, dict, but let list, OrderedDicts, sequence go through as usual.
In all cases I'd let the function do the same as it has been doing so far.

Any comment?

On Fri, Jul 17, 2020 at 2:52 PM Jared Claypoole 
wrote:

> Hi Roberto,
>
> It looks like you're expecting python sets to do something they're not
> intended to do.  From the docs
> ,
> "A set object is an unordered collection".  Of course when you iterate over
> all the elements they have to come out in some order, but that's an
> implementation choice.  Elements are not even guaranteed to be returned in
> the same order each time!  (Though probably they will be.)
>
> I can see how one might expect enumerate to only make sense for containers
> which have some guaranteed order, but that's not the way it's been designed
> to work.  It simply iterates over any iterable and gives you an index
> counting how many elements have been seen so far*.
>
> In general if you want a container with guaranteed ordering, you probably
> want to use a list or a tuple, or even a dict (which has had ordering
> guarantees since python 3.7).  You might also be interested in the answers
> to this stackoverflow question on implementing an OrderedSet
> in python.
>
>
> * Actually one is able to change the starting value of this index from 0
> to something else, but that's somewhat beside the point.
>
> On Thursday, July 16, 2020 at 5:34:27 PM UTC-4, Roberto wrote:
>>
>> I am starting to wonder why python is so loose on this. I say "python"
>> because the issue appears for enumerate as well. How can I enumerate a set?
>> Still I am allowed to enumerate a set without receiving any warning. Look
>> at this for instance
>>
>> set(["a","b"])==set(["b","a"])
>> list(enumerate(set(["a","b"])))
>> list(enumerate(set(["b","a"])))
>> import sympy as sp
>> _a, _b = sp.symbols('a b')
>> set([_a,_b])==set([_b,_a])
>> list(enumerate(set([_a,_b])))
>> list(enumerate(set([_b,_a])))
>>
>>
>> Funny enough, moving this code from one notebook to another may change
>> the order in which the sets are ordered. In all cases they are ordered in
>> the same way within the same notebook, but you and I running the same code
>> may get different outcomes!
>> I do not know if this is special with sets of sympy symbols, but I would
>> have said that deep down enumerate should throw a warning when you try to
>> enumerate a set.
>>
>>
>>
>> On Thursday, July 9, 2020 at 9:55:15 PM UTC+2, Aaron Meurer 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  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 sy...@googlegroups.com.
>>> > To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/sympy/c1517b79-490b-4a1b-b526-3e3842b55fbco%40googlegroups.com.
>>>
>>>
>> --
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> "sympy" group.
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Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[Jared Claypoole]

Hi Roberto,

It looks like you're expecting python sets to do something they're not 
intended to do.  From the docs 
, 
"A set object is an unordered collection".  Of course when you iterate over 
all the elements they have to come out in some order, but that's an 
implementation choice.  Elements are not even guaranteed to be returned in 
the same order each time!  (Though probably they will be.)

I can see how one might expect enumerate to only make sense for containers 
which have some guaranteed order, but that's not the way it's been designed 
to work.  It simply iterates over any iterable and gives you an index 
counting how many elements have been seen so far*.

In general if you want a container with guaranteed ordering, you probably 
want to use a list or a tuple, or even a dict (which has had ordering 
guarantees since python 3.7).  You might also be interested in the answers 
to this stackoverflow question on implementing an OrderedSet 
in python.


* Actually one is able to change the starting value of this index from 0 to 
something else, but that's somewhat beside the point.

On Thursday, July 16, 2020 at 5:34:27 PM UTC-4, Roberto wrote:
>
> I am starting to wonder why python is so loose on this. I say "python" 
> because the issue appears for enumerate as well. How can I enumerate a set? 
> Still I am allowed to enumerate a set without receiving any warning. Look 
> at this for instance
>
> set(["a","b"])==set(["b","a"])
> list(enumerate(set(["a","b"])))
> list(enumerate(set(["b","a"])))
> import sympy as sp
> _a, _b = sp.symbols('a b')
> set([_a,_b])==set([_b,_a])
> list(enumerate(set([_a,_b])))
> list(enumerate(set([_b,_a])))
>
>
> Funny enough, moving this code from one notebook to another may change the 
> order in which the sets are ordered. In all cases they are ordered in the 
> same way within the same notebook, but you and I running the same code may 
> get different outcomes!
> I do not know if this is special with sets of sympy symbols, but I would 
> have said that deep down enumerate should throw a warning when you try to 
> enumerate a set.
>
>
>
> On Thursday, July 9, 2020 at 9:55:15 PM UTC+2, Aaron Meurer 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  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 sy...@googlegroups.com. 
>> > To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/sympy/c1517b79-490b-4a1b-b526-3e3842b55fbco%40googlegroups.com.
>>  
>>
>>
>

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Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[Roberto]

I am starting to wonder why python is so loose on this. I say "python" 
because the issue appears for enumerate as well. How can I enumerate a set? 
Still I am allowed to enumerate a set without receiving any warning. Look 
at this for instance

set(["a","b"])==set(["b","a"])
list(enumerate(set(["a","b"])))
list(enumerate(set(["b","a"])))
import sympy as sp
_a, _b = sp.symbols('a b')
set([_a,_b])==set([_b,_a])
list(enumerate(set([_a,_b])))
list(enumerate(set([_b,_a])))


Funny enough, moving this code from one notebook to another may change the 
order in which the sets are ordered. In all cases they are ordered in the 
same way within the same notebook, but you and I running the same code may 
get different outcomes!
I do not know if this is special with sets of sympy symbols, but I would 
have said that deep down enumerate should throw a warning when you try to 
enumerate a set.



On Thursday, July 9, 2020 at 9:55:15 PM UTC+2, Aaron Meurer 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  > 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 sy...@googlegroups.com . 
> > To view this discussion on the web visit 
> https://groups.google.com/d/msgid/sympy/c1517b79-490b-4a1b-b526-3e3842b55fbco%40googlegroups.com.
>  
>
>

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Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[roberto franceschini]

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  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
>  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
> >  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
> > >>  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 
> 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+un

Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[roberto franceschini]

Not sure at all why you say so.
 Adding extra output to the function is excess baggage in my opinion.
Indeed free_symbols is a great idea from the sympy developers. I understand
why technically one wants to give it as a set, because after all the names
are truly meant to be unique. What we need here is just a more transparent
conversion to lost or a block for when set are fed to lambdify.

I am  not very much expert with pull requests but I am working on one. I
just need to figure how to import my forked version of dumpy instead of the
one from pip. After that I can test my proposed change of lambdify.



On Fri, Jul 10, 2020, 18:47 Oscar Benjamin 
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
>  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
> >>  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 
> 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.
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> .
> >>
> >> --
> >> 

Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[Aaron Meurer]

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
 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
>  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 
> >  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
> >>  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  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  
> >> >> 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.
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> >> >> https://groups.google.com/d/msgid/sympy/CAKgW%3D6KuqnjJHTObyDxK0tvaF_Frxzd-MfyQSY94v-oTUWyNAg%40mail.gmail.com.
> >> >
> >> > --
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> >> > Groups "sympy" group.
> >> > To unsubscribe from this

Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[Oscar Benjamin]

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
 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  
> 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
>>  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  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  
>> >> 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 
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>> > To unsubscribe from this group and stop receiving emails from it, send an 
>> > email to sympy+unsubscr...@googlegroups.com.
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>> > https://groups.google.com/d/msgid/sympy/CAJxM9JqSoqQQkYH9UUXGyXNqRtY9VHJxKByc8Fv8%2BPaqFudP6w%40mail.gmail.com.
>>
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>
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Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[roberto franceschini]

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 
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
>  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  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 
> 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.
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> .
>
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> .
>

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Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[Oscar Benjamin]

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
 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  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  
>> 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.
>>
>> --
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>
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Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[roberto franceschini]

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  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 
> 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
> .
>
> --
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> "sympy" group.
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> email to sympy+unsubscr...@googlegroups.com.
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> .
>

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Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[Aaron Meurer]

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  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.
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Re: [sympy] lambdify list of arguments converted silently, why not throw a warning?

[Davide Sandona']

You can wrap lambdify into a new function:

def get_lambda(expr, modules="numpy", **kwargs):
from sympy.utilities.iterables import ordered
signature = list(ordered(expr.free_symbols))
return signature, lambdify(signature, expr, modules=modules, **kwargs)

With it, the argument are sorted alphabetically. You can easily see the
list of arguments by printing signature.

Davide.


Il giorno gio 9 lug 2020 alle ore 11:08 Roberto <
franceschini.robe...@gmail.com> ha scritto:

> 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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[sympy] lambdify list of arguments converted silently, why not throw a warning?

[Roberto]

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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