Change the default of the "c_api_binop_methods" directive to False. (GH-3644)

This is a backwards incompatible change that enables Python semantics for special methods by default, while the directive allows users to opt out of it and go back to the previous C-ish Cython semantics.

See https://github.com/cython/cython/issues/2056

Cython/Compiler/Options.py

@@ -177,7 +177,7 @@ _directive_defaults = {
     'auto_pickle': None,
     'cdivision': False,  # was True before 0.12
     'cdivision_warnings': False,
-    'c_api_binop_methods': True,  # Change for 3.0
+    'c_api_binop_methods': False,  # was True before 3.0
     'overflowcheck': False,
     'overflowcheck.fold': True,
     'always_allow_keywords': True,

tests/run/unicode_formatting.pyx

@@ -38,21 +38,21 @@ def mix_format(a, int b, list c):
 
 class PySubtype(unicode):
     def __rmod__(self, other):
-        return f'PyRMOD({other})'
+        return f'PyRMOD({self}, {other})'
 
 
 cdef class ExtSubtype(unicode):
-    def __mod__(one, other):
-        return f'ExtMOD({one}, {other})'
+    def __rmod__(self, other):
+        return f'ExtRMOD({self}, {other})'
 
 
 def subtypes():
     """
     >>> py, ext = subtypes()
     >>> print(py)
-    PyRMOD(-%s-)
+    PyRMOD(PySub, -%s-)
     >>> print(ext)
-    ExtMOD(-%s-, ExtSub)
+    ExtRMOD(ExtSub, -%s-)
     """
     return [
         '-%s-' % PySubtype("PySub"),