JNCIA-DevOps Python And PyEZ — 10 Questions

Question 1

When managing configuration changes via PyEZ Config utility, which context manager ensures that changes are automatically rolled back if an exception occurs within the block?

Accepted Answer

with Config(dev) as cu:. The PyEZ Config utility provides a context manager that automatically handles locking, loading, committing, and rolling back changes if an exception occurs. The syntax 'with Config(dev) as cu:' opens a configuration session that, upon exiting the block, commits changes if no exception occurred, or rolls back if an exception was raised. This built-in behavior ensures atomic configuration changes.

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with Config(dev, mode='private') as cu:

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try: cu.lock() except: cu.rollback()

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cu.commit(rollback_on_error=True)

Question 2

When writing a Python script using PyEZ, how should you handle connection timeout exceptions when attempting to connect to an unreachable Junos device?

Accepted Answer

except ConnectError:. PyEZ raises ConnectError when it fails to establish a NETCONF session with the target device.

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except NetconfConnectionError:

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except DeviceOpenError:

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except socket.timeout:

Question 3

You are rendering a Jinja2 template in Python that includes a loop over a list of VLANs. Which Jinja2 block syntax correctly iterates over a list named 'vlan_list'?

Accepted Answer

{% for vlan in vlan_list %} ... {% endfor %}. Jinja2 uses `{% %}` delimiters for control-flow statements such as `for`, `if`, and `set`, and requires an explicit `{% endfor %}` to close the loop. The `{{ }}` syntax is reserved for expression output (printing values), so it cannot open a loop. Option C is the only choice that uses the correct statement delimiters and matching end tag.

Answer

{{ for vlan in vlan_list }} ... {{ endfor }}

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[for vlan in vlan_list] ... [endfor]

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<% for vlan in vlan_list %> ... <% endif %>

Question 4

When configuring a JSNAPy test file, which section defines the specific RPCs or CLI commands that should be executed to gather operational data?

Accepted Answer

command: or rpc:. In a JSNAPy test file, the 'command:' or 'rpc:' section defines the specific CLI commands or RPCs to execute on the device to gather operational data. This section is part of the test definition and tells JSNAPy what data to collect for snapshotting and comparison.

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action:

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device_credentials:

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template:

Question 5

You need to write a Python script that extracts interface status from a Junos device using PyEZ and converts the XML output directly into a Python dictionary. Which utility or function can assist with this conversion?

Accepted Answer

Using PyEZ Table and View abstractions. PyEZ Table and View abstractions are designed to parse XML output from Junos devices into structured Python objects, including dictionaries. You define a View that maps XML elements to Python attributes, and a Table that uses the View to return a list of dictionaries. This is the idiomatic way to convert XML to Python data structures in PyEZ.

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dev.rpc.convert_to_dict()

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json.loads(dev.rpc.get_interface_information())

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etree.to_dict()

Question 6

When designing a custom PyEZ Table and View mapping in Python, what configuration parameter in the YAML definition file specifies the RPC or CLI command executed to gather the raw data?

Accepted Answer

rpc:. In a PyEZ Table/View YAML definition, the rpc: key specifies the Junos RPC (or CLI command) that the Table uses to retrieve raw data from the device. When the Table's get() method is called, PyEZ executes the RPC named under rpc: and passes the response to the View for parsing.

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get-rpc:

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exec:

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command_string:

Question 7

You are writing a script that uses PyEZ to load a Junos configuration file, but you want to replace an entire hierarchy level (e.g., protocols bgp) rather than merging the changes. Which parameter should you pass to the load method?

Accepted Answer

action='replace'. The action='replace' parameter tells PyEZ to replace the specified hierarchy level in the candidate configuration.

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overwrite=True

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merge=False

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mode='override'

Question 8

Which Python library does PyEZ depend on under the hood for managing secure SSH connections and NETCONF framing?

Accepted Answer

ncclient. PyEZ depends on ncclient under the hood for managing secure SSH connections and NETCONF framing. ncclient is a Python library that implements the NETCONF protocol and handles SSH transport, XML framing, and RPC execution. PyEZ wraps ncclient to provide a higher-level API for Junos devices.

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paramiko

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fabric

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netmiko

Question 9

When executing a PyEZ RPC call that returns a large dataset (e.g., massive routing table), how can you handle the output efficiently without exhausting local memory?

Accepted Answer

Using parser generators or iterator arguments supported by specific RPC wrappers. Using generators or streaming options in RPC handling prevents loading massive XML trees entirely into memory.

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etree.iterparse() directly on the raw socket stream

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dev.rpc.get_route_information(normalize=True)

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dev.stream_rpc()

Question 10

You are building a custom PyEZ application and need to catch exceptions specific to configuration parsing failures returned by Junos. Which exception class should your script import?

Accepted Answer

from jnpr.junos.exception import ConfigError. The jnpr.junos.exception module is the canonical location for all PyEZ exception classes, and ConfigError is the specific exception raised when Junos returns a configuration parsing or load failure (for example, a syntax error detected by the CLI/commit check). Importing it from jnpr.junos.exception allows the script to catch configuration-related failures distinctly from connection or RPC errors. This is the documented pattern in Juniper's PyEZ library for handling config load errors.

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from jnpr.junos.device import ConfigurationFailed

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from jnpr.junos.utils.config import ConfigError

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from jnpr.junos.exception import ParseError