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 administrator is writing a playbook to manage multiple web servers. The playbook uses a variable "server_facts" which is a list of dictionaries with keys "hostname", "ip", and "status". The administrator needs to extract a list of all hostnames where status is "online". The administrator writes:
- name: Get online hosts
set_fact:
online_hosts: "{{ server_facts | selectattr('status', '==', 'online') | map(attribute='hostname') | list }}"
However, when running the playbook, the "selectattr" filter fails with an error: "Invalid data passed to filter". The administrator checks the structure of "server_facts" and confirms it is a list of dicts with the expected keys. What is the most likely cause of the error?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The "status" key exists but its value is not consistently a string; some entries have integer 0/1 instead of "online"/"offline".
The `selectattr` filter in Ansible uses Jinja2's `selectattr` which relies on Python's `attrgetter` and comparison operators. If the `status` key exists but its value is not consistently a string (e.g., some entries have integer 0/1 instead of 'online'/'offline'), the equality comparison `'==', 'online'` will fail because an integer cannot be compared to a string in this context, causing an 'Invalid data passed to filter' error. The administrator confirmed the structure is correct, so the issue is likely a type mismatch in the values.
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.
✓
The "status" key exists but its value is not consistently a string; some entries have integer 0/1 instead of "online"/"offline".
Why this is correct
Mismatched types cause the comparison to fail.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The "map" filter cannot be chained with "selectattr" directly.
Why it's wrong here
Chaining is allowed and common.
✗
The "list" filter is unnecessary and causes the error.
Why it's wrong here
The list filter is valid and not the cause.
✗
The "selectattr" filter requires Python 3.8 or later.
Why it's wrong here
selectattr works with older Python versions; the error is not version-related.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the error is about filter chaining or syntax, but the real issue is data type inconsistency—specifically that `selectattr` performs strict equality checks and fails when comparing mismatched types like integers and strings.
Detailed technical explanation
How to think about this question
Under the hood, `selectattr` uses Python's `operator.attrgetter` to retrieve the attribute and then applies the test condition. If the attribute value is an integer (e.g., 1) and the test string is 'online', the comparison `1 == 'online'` raises a `TypeError` in Python 3 (though in Python 2 it would silently return False). This is a common pitfall when data comes from mixed sources like JSON (which may parse integers) or dynamic inventories where status values are not normalized to strings.
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.
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: The "status" key exists but its value is not consistently a string; some entries have integer 0/1 instead of "online"/"offline". — The `selectattr` filter in Ansible uses Jinja2's `selectattr` which relies on Python's `attrgetter` and comparison operators. If the `status` key exists but its value is not consistently a string (e.g., some entries have integer 0/1 instead of 'online'/'offline'), the equality comparison `'==', 'online'` will fail because an integer cannot be compared to a string in this context, causing an 'Invalid data passed to filter' error. The administrator confirmed the structure is correct, so the issue is likely a type mismatch in the values.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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