Using __slots__

[Midnighter]

I'm working on a package that makes heavy use of sympy and we would like symengine to be a drop-in replacement. Since in our context there might be anywhere from a few to hundreds of thousands of variables, I'd like to build the variables using __slots__.

That approach works perfectly when inheriting from sympy.Dummy but unfortunately not when subclassing from symengine.Symbol. (I'm building on top of symengine 0.3 so I couldn't find Dummy there.)

Would it be hard for you to redefine your Python class interface to use __slots__?

[isuruf]

I'm not familiar with __slots__ can you give a small example that doesn't work?

[Midnighter]

Sure, please take a look at the linked notebook. Basically, classes with slots are more compact and deterministic. However, if you don't define __slots__ in your class, Python automatically defines the __dict__ attribute for you. If any class in your parent hierarchy does this, it is pointless to use slots in child classes because __dict__ is already defined. The linked StackOverflow answer in my above comment has a very extensive description and I recommend reading it when you have the time. Please note that in the notebook I also care about the __weakref__ attribute because my code needs it but that actually doesn't really relate to this issue.

[isuruf]

Note that all symengine classes deriving from Basic has only one attribute. The pointer to the C++ object.

Cython extension classes like Basic has a mechanism similar to __slots__. So, if you do pi.__dict__ it will throw an error. (pi is an object of type Constant which is a Cython extension class)

All the classes in symengine used to be Cython extension classes and then some were changed to be regular Python classes so that __new__ could be used for simulating SymPy behaviour of Add(1, 2) returning an Integer class.

Symbol was changed to a regular Python class at 83bd7ae and I'm not sure why. There are two options,

1. Change Symbol to be a Cython extension class
2. Define __slots__ = () in class Symbol

Both should work. I'm not sure which is the best. I guess we can go with 1 and switch to option 2 if that doesn't work.

Can you send a PR with the above change and a test case?

[Midnighter]

Option 2. I can easily do, while for option 1. I feel that I know too little about symengine. However, if that is your preferred way I can make a suggestion and you can review it.

[isuruf]

Option 1 is basically changing class Symbol(Expr) to cdef class Symbol(Expr)