The correct implementation is return s.isdigit(), which uses Python’s built-in string method to check if a string contains only digits. The isdigit() method iterates over every character in the string and returns True only when all characters are classified as digits, including standard 0-9 and other Unicode numeric characters, making it the precise tool for verifying digit-only strings. On the Certified Associate Python Programmer PCAP exam, this question tests your understanding of string methods and their correct application, often appearing as a multiple-choice trap where alternatives like isnumeric() or isdecimal() are offered—isdigit() is the safest choice for typical digit checks because it excludes fractions and superscripts that isnumeric() might include. A common memory tip is to think of “digit” as the narrowest category: if you need only 0-9 and basic numeric characters, isdigit() is your go-to, while isdecimal() is even stricter and isnumeric() is broader. Remember the mnemonic “DIGit = Direct, Is Good” to recall that isdigit() directly answers the digit-only check.
PCAP Strings Practice Question
This PCAP practice question tests your understanding of strings. 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 function is supposed to return True if a string contains only digits, and False otherwise. Which implementation uses a Python string method correctly?
Why wrong: More restrictive, excludes superscript digits and other Unicode digits.
B
return s.isnumeric()
Why wrong: Also returns True for numeric characters like fractions, which may not be considered digits in all contexts.
C
return s.isalnum() and not s.isalpha()
Why wrong: Returns True for strings with only digits, but also for strings with letters and digits (alphanumeric) as long as there is at least one digit.
D
return s.isdigit()
Correctly returns True for strings containing only digits.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
return s.isdigit()
isdigit() checks if all characters in the string are digits (0-9 and other Unicode digits), which is the standard method for this purpose.
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.
✗
return s.isdecimal()
Why it's wrong here
More restrictive, excludes superscript digits and other Unicode digits.
✗
return s.isnumeric()
Why it's wrong here
Also returns True for numeric characters like fractions, which may not be considered digits in all contexts.
✗
return s.isalnum() and not s.isalpha()
Why it's wrong here
Returns True for strings with only digits, but also for strings with letters and digits (alphanumeric) as long as there is at least one digit.
✓
return s.isdigit()
Why this is correct
Correctly returns True for strings containing only digits.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which PCAP exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Strings — This question tests Strings — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: return s.isdigit() — isdigit() checks if all characters in the string are digits (0-9 and other Unicode digits), which is the standard method for this purpose.
What should I do if I get this PCAP question wrong?
Identify which PCAP exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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This PCAP 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 PCAP exam.
Question Discussion
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