Fix error message in toPythonObj (#6524)

diff --git a/src/api/python/cvc5.pxi b/src/api/python/cvc5.pxi
index f38a953eec639f7c36c6324ea6deb72620d04061..fc14c1fcaf70300ed48d8b8693e8c705251742d6 100644 (file)
--- a/src/api/python/cvc5.pxi
+++ b/src/api/python/cvc5.pxi
@@ -663,7 +663,7 @@ cdef class Solver:
                 op.cop = self.csolver.mkOp(k.k, <int?> arg0)
             else:
                 raise ValueError("Unsupported signature"
-                                 " mkOp: {}".format(" X ".join([k, arg0])))
+                                 " mkOp: {}".format(" X ".join([str(k), str(arg0)])))
         else:
             if isinstance(arg0, int) and isinstance(arg1, int):
                 op.cop = self.csolver.mkOp(k.k, <int> arg0,