PCEP Practice Question: Functions, Tuples, Dictionaries and Exceptions
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?
⚠ Common exam trap
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.
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
✓
count = sum(log[1] == 'ERROR' for log in logs)
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.
Answer analysis
Option-by-option breakdown
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
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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.