JNCIA-DevOps Python And PyEZ Practice Test 3 — 15 Questions

Question 1

In a Jinja2 template designed for Junos configuration, how do you correctly output the value of a variable named 'hostname'?

Accepted Answer

{{ hostname }}. Jinja2 uses double curly braces {{ }} as the expression delimiter to output the value of a variable into the rendered template. Writing {{ hostname }} substitutes the value of the 'hostname' variable at render time. This is the standard Jinja2 syntax for variable interpolation and is used throughout Junos configuration templates.

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${hostname}

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{% hostname %}

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<< hostname >>

Question 2

What is JSNAPy primarily used for in Junos network automation?

Accepted Answer

Taking operational state snapshots and verifying device health. JSNAPy (Junos Snapshot Administrator in Python) is a Python tool that captures operational state snapshots from Junos devices and compares them against a baseline to verify health and detect drift. It is commonly used for pre/post-change validation and compliance checks. It does not compile CLI commands, perform firmware upgrades, or generate configuration templates.

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Compiling Junos CLI operational commands into Python bytecode

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Performing automated firmware upgrades across clusters

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Generating static configuration templates

Question 3

You want to run a JSNAPy verification test via Python code. Which Python class should you import and instantiate to execute the snapshot comparison programmatically?

Accepted Answer

from jnpr.jsnapy import SnapAdmin. The SnapAdmin class from the jnpr.jsnapy module is the main entry point for programmatically running JSNAPy operations, including taking snapshots and comparing them. You import it with 'from jnpr.jsnapy import SnapAdmin' and instantiate it to call methods like snap() and check(). This is the documented Python API for JSNAPy.

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from jnpr.jsnapy.verify import VerifyEngine

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from jnpr.junos.utils.jsnapy import JSNAPy

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from jnpr.jsnapy.runner import JSNAPyRunner

Question 4

When executing an RPC call in PyEZ, what format is typically returned by default if you do not parse it into another structure?

Accepted Answer

An XML Element (lxml.etree). PyEZ RPC calls return an ElementTree object (XML Element) representing the response from the Junos device.

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A JSON dictionary

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A raw plain text string

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A Python list of strings

Question 5

In a Python script utilizing PyEZ, what method must be called on the Device instance after all configuration and operational tasks are complete to properly terminate the NETCONF session?

Accepted Answer

dev.close(). In PyEZ, the Device object maintains an active NETCONF session over SSH (port 830) that must be explicitly torn down. The dev.close() method cleanly closes the NETCONF session, releases the underlying SSH transport, and frees associated resources. Without calling close(), the session may linger until timeout, consuming VTY/session slots on the Junos device.

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dev.terminate()

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dev.end_session()

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dev.disconnect()

Question 6

When using Jinja2 templates in Python to generate configurations, how can you load a template file from disk prior to rendering it with variables?

Accepted Answer

Template(open('template.j2').read()). The Jinja2 `Template` class accepts a template source string, so reading the file contents with `open('template.j2').read()` and passing that string to `Template()` is a valid way to load a template from disk. This is the standard minimal pattern when you don't need Jinja2's file-system loader features. The other options reference methods or modules that do not exist in the Jinja2 API.

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template.open('template.j2')

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import_template('template.j2')

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jinja2.load_file('template.j2')

Question 7

An automation script needs to check if a Junos device supports a specific feature before executing an RPC. Which PyEZ property can be checked to inspect the software version loaded on the device?

Accepted Answer

dev.facts['version']. The PyEZ Device object exposes device facts through the `dev.facts` dictionary, and the loaded Junos software version is stored under the key `'version'`. Accessing `dev.facts['version']` returns the string reported by the device (for example, '21.4R3-S2.6'), which a script can parse to decide whether a feature RPC is supported. This is the canonical PyEZ pattern for version inspection.

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dev.get_version()

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dev.version

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dev.os_version

Question 8

You are writing a script that performs multiple configuration changes inside a single PyEZ Config context. How can you verify that the candidate configuration has syntax errors before committing it?

Accepted Answer

cu.validate(). The PyEZ Config utility provides the `cu.validate()` method to check the candidate configuration for syntax errors before committing. It performs a commit check on the device, returning any errors without actually committing the configuration, allowing the script to verify correctness inside a Config context.

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cu.test_syntax()

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cu.verify()

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cu.check()

Question 9

What Jinja2 feature allows you to include the contents of another template file into your main configuration template?

Accepted Answer

{% include 'filename.j2' %}. Jinja2's {% include 'filename.j2' %} statement renders the contents of another template file inline at that point in the parent template. This is the standard mechanism for modularizing templates — common config blocks (e.g., standard interface settings, SNMP communities) can be stored in separate files and included where needed. The included template shares the parent's variable context.

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{% insert 'filename.j2' %}

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{% import 'filename.j2' %}

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Question 10

In JSNAPy, what file format is used to define test cases and expected operational states?

Accepted Answer

YAML. JSNAPy uses YAML configuration files for defining tests and expected values.

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INI

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XML

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JSON

Question 11

Which Jinja2 construct is used to define reusable blocks of template code that can be called with arguments like a function?

Accepted Answer

{% macro %} ... {% endmacro %}. Macros in Jinja2 act like functions for templates.

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{% def %} ... {% enddef %}

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{% block %} ... {% endblock %}

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{% function %} ... {% endfunction %}

Question 12

When writing a Python script that connects to multiple Junos devices concurrently using PyEZ, which Python module is commonly used to manage thread pooling and parallel execution?

Accepted Answer

concurrent.futures. The concurrent.futures module is the standard Python library for managing thread pools and parallel execution. It provides ThreadPoolExecutor and ProcessPoolExecutor, which are commonly used with PyEZ to connect to multiple Junos devices concurrently. This is the recommended approach for parallel device operations in Python scripts.

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jnpr.junos.parallel

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multiprocessing.device

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asyncio.netconf

Question 13

You have captured a baseline snapshot using JSNAPy and want to compare a newly taken snapshot against that baseline. Which JSNAPy command-line action executes this comparison?

Accepted Answer

jsnapy --check. JSNAPy's --check action compares a freshly captured snapshot against the stored baseline snapshot and reports any differences. It is the standard command for post-change verification, typically run after a configuration commit to detect drift from the known-good baseline. The --snap action captures the snapshot, while --check performs the comparison.

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jsnapy --test

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jsnapy --verify

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jsnapy --compare

Question 14

When using PyEZ to push a configuration, you want to log out all NETCONF XML traffic exchanged between the script and the Junos device for debugging purposes. How do you enable this logging in Python?

Accepted Answer

Configuring Python logging for the 'jnpr.junos' logger with DEBUG level. PyEZ uses Python's standard `logging` module and emits all NETCONF XML traffic under the `jnpr.junos` logger hierarchy. Setting that logger to DEBUG level (via `logging.getLogger('jnpr.junos').setLevel(logging.DEBUG)` plus a handler) causes the full request/response XML to be logged. There is no PyEZ-specific debug flag or `dev.debug` attribute that performs this function.

Answer

import jnpr.junos.debug; jnpr.junos.debug.enable()

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dev.rpc.trace(enabled=True)

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dev.debug = True

Question 15

When writing a Python script to interact with Junos devices, you want to ensure that password credentials are not hardcoded in the source code. What is a recommended best practice supported by PyEZ?

Accepted Answer

Using SSH key-based authentication or environment variables/config files (.junodes). PyEZ natively supports configuration files like ~/.junodes or passing parameters dynamically, but also respects environment variables or SSH keys.

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Disabling authentication in the script

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Storing credentials in plaintext in a public GitHub repository

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Hardcoding credentials in base64 encoding