def _has_explicit_output(self, expr, func):
        """
        Return whether the *expr* call to *func* (a ufunc) features an
        explicit output argument.
        """
        nargs = len(expr.args) + len(expr.kws)
        if expr.vararg is not None:
            # XXX *args unsupported here, assume there may be an explicit
            # output
            return True
        return nargs > func.nin

        Return whether the *expr* call to *func* (a ufunc) features an
        explicit output argument.
        
numba/np/ufunc/array_exprs.py