Do you really need the Python form, or is the Cadabra input form perhaps better? The Python form gives greek indices in the form of Unicode characters, which the Cadabra notebook does not print because the LaTeX backend does not handle them correctly. But you can do
which will produce
You can feed that back into Cadabra, e.g.
ex2=Ex("2 * "+ex.input_form());
which prints $2\alpha$.