Python 3.9 compatibility

[xmo-odoo]

Python 3.9 is not exactly there yet, but this can serve as a reminder of things to come:

• COMPARE_OP split into 4 opcodes (python/cpython@9af0e47)

• LOAD_ASSERTION_ERROR bytecode for assert statements

  assert is compiled to a simple conditional:

   >>> @dis.dis
   ... def foo(): 
   ...     assert a
   ... 
     3           0 LOAD_GLOBAL              0 (a)
                 2 POP_JUMP_IF_TRUE         8
                 4 LOAD_GLOBAL              1 (AssertionError)
                 6 RAISE_VARARGS            1
           >>    8 LOAD_CONST               0 (None)
                10 RETURN_VALUE
   >>> @dis.dis
   ... def foo():
   ...     if not a:
   ...             raise AssertionError
   ... 
     3           0 LOAD_GLOBAL              0 (a)
                 2 POP_JUMP_IF_TRUE         8
   
     4           4 LOAD_GLOBAL              1 (AssertionError)
                 6 RAISE_VARARGS            1
           >>    8 LOAD_CONST               0 (None)
                10 RETURN_VALUE
  

  however in order to ensure it can always properly load AssertionError at runtime, in 3.9 it gets a dedicated opcode for this. Check if we have assertions in safe-eval'd code and add the opcode if so.