REF: expose is_definitely_invalid_key()

Author: toobaz

pandas/_libs/index.pyx

@@ -28,7 +28,7 @@ from cpython.slice cimport PySlice_Check
 cdef int64_t iNaT = util.get_nat()
 
 
-cdef inline is_definitely_invalid_key(object val):
+cpdef inline bint is_definitely_invalid_key(object val):
     if PyTuple_Check(val):
         try:
             hash(val)