Unable to iterate over a nested list in Python ?

[bashar1aziz@gmail.com]

I am creating a service module apply interface configs. I am facing a number of errors in my Python code while referencing a leaf in a nested list.

---YANG---:

list endpoints {
key device;
leaf device {
type leafref {
path "/ncs:devices/ncs:device/ncs:name";
}
}
list intf {
key intf_id;
leaf intf_id {
type string;
}

}

}

---Python---:

template = ncs.template.Template(service)
vars = ncs.template.Variables()

for i in service.intf[intf_id]:
vars.add('intf-id', i.intf_id)
#vars.add('port-id', i.port_id)
template.apply('device_provisioning-template', vars)

---error I am getting---:

errors: reason: Python cb_create error. 'ListElement' object has no attribute 'intf'

[tcragg1]

I think the problem is that you are trying to iterate over a list element rather than over the list as a whole. Try removing the "[intf_id]" from the end of the for loop line to make it iterate over the list.

[snovello · Accepted solution]

hello Bashar,

you have nested lists , intf inside endpoints so you will need nested for loops

for endpoint in service.endpoints:

   for interface in endpoint.intf:

     vars.add('intf-id', interface.intf_id )

the error is saying there is no intf attribute in service, that is because the intf list is nested inside the endpoints list.

Stefano

[BasharAziz]

Nested for loops in Python were needed. Awesome now it works like a charm. 

Thank you Stefano.

[ZAhmad04890]

Hi snovello,

In the above example code, I am not clear about the usage of passing the object "service" passed in statement

"template = ncs.template.Template(service)".

when we pass "service" as object what difference it makes as compared to if we pass the object "endpoint" as

"template = ncs.template.Template(endpoint)" which is essentially "service.endpoints" .Thanks.

for endpoint in service.endpoints:

for interface in endpoint.intf:

vars.add('intf-id', interface.intf_id )

template = ncs.template.Template(endpoint)

vs

for endpoint in service.endpoints:

for interface in endpoint.intf:

vars.add('intf-id', interface.intf_id )

template = ncs.template.Template(service)

[vleijon]

It forms the initial context for any xpath expressions in the template.

[ZAhmad04890]

Hi, when using nested for loops or similar logic , how can we print the values of service variables e.g "endpoint.intf"

or "service.endpoint" ? as shown below, in iPython editor? I believe we also need to import some ncs service libraries for this functionality to work and need a running NSO service instance as well? Thanks

for endpoint in service.endpoints:

  for interface in endpoint.intf:

      print(interface, endpoint)

vars.add('intf-id', interface.intf_id )

[vleijon]

So, you can use ncs_pycli (https://github.com/NSO-developer/ncs_pycli) to do it from the command line, that allows you to easily investigate the data tree. Of course you can just run the same things directly in any tool you want.

[snovello]

Hello,

there are a couple of nice githubs that do this very confortably for you. one starts  ipython straight from the nso cli, the other is a shell wrapper.

see https://www.google.com/search?q=cisco+nso+ipython

I use a tiny script, which I include here, you can copy and paste into a file that is in your path, I have it called ncs_py_cli

#!/usr/bin/env python3
from __future__ import print_function
import ncs
import IPython

if __name__ == '__main__':
    m = ncs.maapi.Maapi()
    sess = m.start_user_session('admin', 'system', [])
    trans = m.start_trans(ncs.RUNNING, ncs.READ_WRITE)

    x = ncs.maagic.get_root(trans)

    print("Your maagic object 'x -> %s' is now prepared... go have some fun!" %
          (str(x)))
    IPython.embed(display_banner=False)

it starts an ipython session where you have the variables m, sess, trans, and x and from there you can navigate to where you want.