Quick Answer
The answer is `count = sum(log[1] == 'ERROR' for log in logs)`, which correctly counts elements in a list of tuples with a condition by leveraging Python’s implicit boolean-to-integer conversion. This works because the generator expression evaluates `log[1] == 'ERROR'` as `True` (1) or `False` (0) for each tuple, and `sum()` adds those ones and zeros to produce the exact count of ERROR logs. On the PCEP exam, this tests your understanding of generator expressions and the `sum()` function as a compact alternative to a manual loop—a common trap is trying to use `len()` on a filtered list, which wastes memory. Remember that `sum()` treats `True` as 1, so you can count any condition without creating an intermediate list. A handy mnemonic: “Sum the booleans to count the trues.”
This PCEP practice question tests your understanding of functions, tuples, dictionaries and exceptions. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A server logs are stored as a list of tuples: `logs = [('2024-01-10', 'INFO', 'Started'), ('2024-01-10', 'ERROR', 'Disk full')]`. A developer wants to count how many ERROR logs exist. Which code snippet correctly counts them?
count = logs.count(('ERROR',))
Why wrong: count() does not work with partial tuple matching.
count = sum(log[1] == 'ERROR' for log in logs)
Sum of booleans gives the count.
count = [log for log in logs if log[1] == 'ERROR']
Why wrong: This creates a list, not a count.
count = len(logs)
Why wrong: This counts all logs, not just errors.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
count = sum(log[1] == 'ERROR' for log in logs)
Option B uses a generator expression with `sum()` to count how many tuples in the `logs` list have the second element equal to `'ERROR'`. The expression `log[1] == 'ERROR'` evaluates to `True` (which is treated as 1) or `False` (0) for each tuple, and `sum()` adds them up, giving the correct count of ERROR logs.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
count = logs.count(('ERROR',))
Why it's wrong here
count() does not work with partial tuple matching.
count = sum(log[1] == 'ERROR' for log in logs)
Why this is correct
Sum of booleans gives the count.
Related concept
Read the scenario before looking for a memorised answer.
count = [log for log in logs if log[1] == 'ERROR']
Why it's wrong here
This creates a list, not a count.
count = len(logs)
Why it's wrong here
This counts all logs, not just errors.
Common exam traps
Python Institute often tests the distinction between `list.count()` (which requires an exact match of the entire element) and counting via a conditional expression with `sum()`, leading candidates to mistakenly think `count()` can filter by a partial tuple or a specific field.
Detailed technical explanation
The `sum()` function with a generator expression is a Pythonic idiom for counting boolean conditions because `True` is implicitly converted to 1 and `False` to 0 during arithmetic. This approach is memory-efficient as it avoids building an intermediate list, unlike a list comprehension wrapped in `len()`. In real-world log analysis, this pattern is commonly used to quickly tally specific event types without loading all filtered results into memory.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the PCEP 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
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FAQ
Functions, Tuples, Dictionaries and Exceptions — This question tests Functions, Tuples, Dictionaries and Exceptions — Read the scenario before looking for a memorised answer..
The correct answer is: count = sum(log[1] == 'ERROR' for log in logs) — Option B uses a generator expression with `sum()` to count how many tuples in the `logs` list have the second element equal to `'ERROR'`. The expression `log[1] == 'ERROR'` evaluates to `True` (which is treated as 1) or `False` (0) for each tuple, and `sum()` adds them up, giving the correct count of ERROR logs.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PCEP practice question is part of Courseiva's free Python Institute certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCEP exam.
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