equality check of python objects in lua

[mfrigerio17]

Hi,
The following code fails with TypeError: __eq__() missing 1 required positional argument: 'rhs'

import lupa

lua = lupa.LuaRuntime(unpack_returned_tuples=True)

class foo: 
    def __init__(self): 
        self.a = 1 
    def __eq__(self, rhs): 
        return self.a==rhs.a
    def __hash__(self) :
        return hash(self.a)

f1 = foo()
f2 = foo()

lua.execute('f1 = python.eval("f1")')
lua.execute('f2 = python.eval("f2")')

print(f1==f2)                        # prints 'True' (correct)
lua.execute('print(f1==f2)')         # prints 'false' (wrong)
lua.execute('print(f1.__eq__(f2))')  # prints 'true' (correct)
lua.execute('print(f1.__eq__(f1))')  # fails

Is it a bug or am I missing something?
Python 3.8.2, Lupa 1.9
Thanks

[scoder]

Yes, I think it makes sense to support this. However, we also have to make sure it produces something reasonable when comparing a Python object to a Lua object.

PR welcome that adds support for the Lua equality operator to Lupa wrapped Python objects, as well as a bunch of tests that show that the behaviour of different Python and Lua objects is "as expected", both left and right of the comparison operator.

[astoff]

Should comparison of wrapped objects (both POBJECTs in Lua and Lua objects in Python) follow the host language semantics or the native language semantics?

I would say they should follow the native language semantics, so e.g. Python lists compare by value in Lua and Lua tables compare by identity in Python. See also #249.