Dynamic update of default value in dynamic forms

Hi,

I was looking for a way to update dynamically the default value of a selectForm.
My code is the following:

%spark2.pyspark
d_var = {}
d_var['one'] = ["0"]
d_var['two'] = ["1"]

keys = []
values = [('0', 'True'), ('1', 'False')]
for key in sorted(d_var.keys()):
keys.append((key, key))

key = z.select('Keys', keys, keys[0][0])
default_value = '0' if key == 'one' else '1'
print default_value
value = z.select('Option', values, default_value)

When I change the selected value in the first select I expect that the second select will be updated but nothing happens, only in the first execution of the paragraph