Question 334 of 518

Transform data with filters and plugins →mediumMultiple ChoiceObjective-mapped

EX294 Transform data with filters and plugins Practice Question

This EX294 practice question tests your understanding of transform data with filters and plugins. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

An Ansible playbook is used to generate configuration files for network devices. The variables are defined in a vars file like: ---

interfaces:

- name: GigabitEthernet1 ip: 192.168.1.1/24 - name: GigabitEthernet2 ip: 10.0.0.1/24

The playbook uses a Jinja2 template to render the config. The template iterates over interfaces and writes "ip address" lines. However, the designer wants to support an additional field "secondary_ips" which is a list of IP addresses (e.g., ["192.168.2.1/24", "192.168.3.1/24"]). In the template, they want to generate multiple "ip address" lines for each interface, one for the primary IP and one for each secondary IP. The following template fragment is used:

{% for iface in interfaces %}
interface {{ iface.name }}
 ip address {{ iface.ip }}
{% for sec in iface.secondary_ips|default([]) %}
 ip address {{ sec }}
{% endfor %}
{% endfor %}

This works when secondary_ips is defined. However, some interfaces have secondary_ips defined as a string (e.g., "192.168.2.1/24") instead of a list. The playbook fails because the inner loop tries to iterate over a string. The engineer wants to normalize the data in the playbook before passing to the template, so that secondary_ips is always a list. Which of the following set_fact tasks will correctly transform the interfaces list to ensure secondary_ips is always a list (even if missing or a string)?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.

Question 1mediummultiple choice

Read the full Ansible explanation →

A
- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': item.secondary_ips | default([]) | split(',') if item.secondary_ips is defined and item.secondary_ips is string else item.secondary_ips | default([])}) }}" loop: "{{ interfaces }}"
Why wrong: Syntax error due to incorrect Jinja2 conditional placement within map.
B
- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': [item.secondary_ips | default('')] | flatten }) }}" loop: "{{ interfaces }}"
Why wrong: Wraps a string in a list, but does not split it; flatten only removes one level of nesting.
C
- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': item.secondary_ips | default([]) | string | split(',') | list}) }}" loop: "{{ interfaces }}"
Why wrong: String conversion of a list produces a representation like "['a','b']", which split by comma yields incorrect elements.
D
- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': (item.secondary_ips is undefined or item.secondary_ips is none) | ternary([], (item.secondary_ips is string) | ternary(item.secondary_ips | split(','), item.secondary_ips))}) }}" loop: "{{ interfaces }}"
Correctly handles undefined, string, and list cases.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': (item.secondary_ips is undefined or item.secondary_ips is none) | ternary([], (item.secondary_ips is string) | ternary(item.secondary_ips | split(','), item.secondary_ips))}) }}" loop: "{{ interfaces }}"

Option D correctly uses the `ternary` filter to handle three cases: when `secondary_ips` is undefined or None (returns an empty list), when it is a string (splits it into a list), and when it is already a list (returns it unchanged). This ensures the template always receives a list for iteration, preventing the 'iteration over string' error.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': item.secondary_ips | default([]) | split(',') if item.secondary_ips is defined and item.secondary_ips is string else item.secondary_ips | default([])}) }}" loop: "{{ interfaces }}"
Why it's wrong here
Syntax error due to incorrect Jinja2 conditional placement within map.
✗
- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': [item.secondary_ips | default('')] | flatten }) }}" loop: "{{ interfaces }}"
Why it's wrong here
Wraps a string in a list, but does not split it; flatten only removes one level of nesting.
✗
- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': item.secondary_ips | default([]) | string | split(',') | list}) }}" loop: "{{ interfaces }}"
Why it's wrong here
String conversion of a list produces a representation like "['a','b']", which split by comma yields incorrect elements.
✓
- set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': (item.secondary_ips is undefined or item.secondary_ips is none) | ternary([], (item.secondary_ips is string) | ternary(item.secondary_ips | split(','), item.secondary_ips))}) }}" loop: "{{ interfaces }}"
Why this is correct
Correctly handles undefined, string, and list cases.
Clue confirmation
The clue words "primary", "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often try to use `default([])` or `split` without handling the case where the variable is already a list, leading to nested lists or string conversion errors, while the correct approach uses `ternary` to conditionally apply transformations based on the data type.

Detailed technical explanation

How to think about this question

The `ternary` filter in Ansible acts as an inline if-else, evaluating a condition and returning one of two values. In Option D, the first ternary checks for undefined/None, returning an empty list; the second ternary checks if the value is a string (using `is string` test) and splits it into a list, otherwise returns the value as-is (which is already a list). This pattern is common when normalizing heterogeneous data from sources like CSV files or user input, ensuring idempotent transformation.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the EX294 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this EX294 question test?

Transform data with filters and plugins — This question tests Transform data with filters and plugins — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: - set_fact: interfaces: "{{ interfaces | map('combine', {'secondary_ips': (item.secondary_ips is undefined or item.secondary_ips is none) | ternary([], (item.secondary_ips is string) | ternary(item.secondary_ips | split(','), item.secondary_ips))}) }}" loop: "{{ interfaces }}" — Option D correctly uses the `ternary` filter to handle three cases: when `secondary_ips` is undefined or None (returns an empty list), when it is a string (splits it into a list), and when it is already a list (returns it unchanged). This ensures the template always receives a list for iteration, preventing the 'iteration over string' error.

What should I do if I get this EX294 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "primary", "always". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 25, 2026

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