Sudeep Sidhu

You have it! Start working.

> I'm also interested in expanding the units module by adding support for cross-unit system conversions. For example, you have a formula expressed in natural units and would like to...

The non-core classes call `.evalf` first and it tries to solve using `evalf_table`. If `evalf_table` fails then it falls back to `_eval_evalf` which is implemented in classes explicitly. Non-core class...

> 3. The `x._eval_evalf` method bypasses the table so it won't e.g. lead to `evalf_add`. `x._eval_evalf` method bypasses the table because it calls `._evalf()` which doesn't make sense to me...

Similar changes are required to `EvalMixin` class also, but these changes would be slightly different because the `EvalMixin` class has it's `option` parameter expanded. https://github.com/sympy/sympy/blob/b3cae120dad022dd83e338df69c45f60dd95efd9/sympy/core/evalf.py#L1384

> The problem with this is that user code and downstream libraries have probably implemented `_eval_evalf` methods that don't take any arguments. That code would break if we suddenly start...

@oscarbenjamin I think I got your point. Correct me if I'm wrong. What we need here is a new `_eval_evalf()` function which would be defined explicitly in subsequent classes and...

@oscarbenjamin Got it! Working on it.

> Then within the sympy codebase all `_eval_evalf` methods should be changed to `_eval_evalf_options` and they should all recurse using the `evalf` function from the `sympy.core.evalf` module (not the `.evalf`,...

I'll give it a try.