Quick Answer
The answer is '00123'. This is correct because the `zfill()` method in Python performs zero padding by adding zeros to the left of the string until it reaches the specified width; since '123' is three characters long and the target width is five, two zeros are prepended to produce '00123'. On the Certified Associate Python Programmer PCAP exam, this question tests your understanding of Python string methods and their behavior with numeric strings, often appearing in sections on built-in functions and string manipulation. A common trap is confusing `zfill()` with right-justification or assuming it works on numeric types directly—remember that `zfill()` is a string method, so the input must be a string, and it only pads zeros, never truncates. For a quick memory tip, think of "z" as "zero-fill from the left," and if the width is less than or equal to the string's length, no padding occurs.
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.
What is the result of the expression '123'.zfill(5)?
'00123'
Correct: Pads with two zeros on the left to reach length 5.
'123'
Why wrong: Incorrect: No padding applied.
'000123'
Why wrong: Incorrect: That would be padding to width 6.
'12300'
Why wrong: Incorrect: Zeros are added on the left, not right.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
'00123'
The `zfill()` method in Python pads the string on the left with zeros until it reaches the specified width. For the string '123' and width 5, it adds two zeros to the left, resulting in '00123'. This is the correct behavior as defined in Python's string methods.
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.
'00123'
Why this is correct
Correct: Pads with two zeros on the left to reach length 5.
Related concept
Read the scenario before looking for a memorised answer.
'123'
Why it's wrong here
Incorrect: No padding applied.
'000123'
Why it's wrong here
Incorrect: That would be padding to width 6.
'12300'
Why it's wrong here
Incorrect: Zeros are added on the left, not right.
Common exam traps
Python Institute often tests the misconception that `zfill()` pads zeros on the right or that the width includes the original string length plus padding, leading candidates to choose options like '000123' or '12300'.
Detailed technical explanation
Under the hood, `zfill()` works by checking if the string starts with a sign character ('+' or '-'); if so, it preserves the sign and pads zeros after it. For numeric strings, this ensures proper zero-padded representation. In real-world scenarios, `zfill()` is commonly used to format numbers with leading zeros for fixed-width output, such as invoice numbers or time values.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Strings — This question tests Strings — Read the scenario before looking for a memorised answer..
The correct answer is: '00123' — The `zfill()` method in Python pads the string on the left with zeros until it reaches the specified width. For the string '123' and width 5, it adds two zeros to the left, resulting in '00123'. This is the correct behavior as defined in Python's string methods.
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 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.
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