Quick Answer
The correct answer is s[0:2], which extracts the substring 'Py' from the string 'Python' by slicing from index 0 up to, but not including, index 2. This works because Python string slicing uses a start:stop syntax where the stop index is exclusive, so indices 0 and 1—'P' and 'y'—are returned. On the Certified Associate Python Programmer PCAP exam, this tests your understanding of both positive and negative indexing, as well as the exclusive nature of the stop value. A common trap is forgetting that negative indices count from the end, so s[0:-4] also works because -4 corresponds to index 2, making the slice identical to s[0:2]. The exam frequently pairs these two equivalent forms to see if you recognize that both produce the same result. Memory tip: think of slicing like a fence—the start post is included, but the stop post is the first one you don't grab.
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.
Which TWO of the following expressions yield the substring 'Py' from the string s = 'Python'?
s[0:-4]
Correct: from 0 to -4 (exclusive), which is indices 0 and 1.
s[0:2:2]
Why wrong: Yields 'P' because step 2 skips the second character.
s[-6:-3]
Why wrong: Yields 'Pyt' (indices -6, -5, -4).
s[0:2]
Correct: indices 0 and 1.
s[0:1]
Why wrong: Yields 'P' only.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
s[0:-4]
Option A is correct because s[0:-4] uses negative indexing to slice from index 0 up to (but not including) index -4, which corresponds to the character 'o' (the fifth character from the end). Since 'Python' has length 6, index -4 is the character at position 2 (0-based), so the slice returns characters at indices 0 and 1, which are 'P' and 'y', yielding 'Py'.
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.
s[0:-4]
Why this is correct
Correct: from 0 to -4 (exclusive), which is indices 0 and 1.
Related concept
Read the scenario before looking for a memorised answer.
s[0:2:2]
Why it's wrong here
Yields 'P' because step 2 skips the second character.
s[-6:-3]
Why it's wrong here
Yields 'Pyt' (indices -6, -5, -4).
s[0:2]
Why this is correct
Correct: indices 0 and 1.
Related concept
Read the scenario before looking for a memorised answer.
s[0:1]
Why it's wrong here
Yields 'P' only.
Common exam traps
Python Institute often tests the interaction between negative indexing and step values, trapping candidates who forget that a step of 2 skips characters or that negative indices count from the end, leading them to select options that return only one character or an incorrect substring.
Detailed technical explanation
Python's slicing with negative indices is equivalent to adding the length of the string to the negative index (e.g., -4 becomes 2 for a 6-character string). The slice s[0:-4] is thus identical to s[0:2], which is the most direct way to get the first two characters. Understanding this equivalence is crucial for efficient string manipulation, especially when dealing with strings of unknown or variable length, such as parsing file extensions or trimming paths.
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: s[0:-4] — Option A is correct because s[0:-4] uses negative indexing to slice from index 0 up to (but not including) index -4, which corresponds to the character 'o' (the fifth character from the end). Since 'Python' has length 6, index -4 is the character at position 2 (0-based), so the slice returns characters at indices 0 and 1, which are 'P' and 'y', yielding 'Py'.
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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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. What is the result of the expression 'Hello'[1:3]?
easyWhy A: In Python, string slicing uses the syntax `string[start:stop]`, where `start` is inclusive and `stop` is exclusive. For `'Hello'[1:3]`, the indices are: index 1 = 'e', index 2 = 'l', and index 3 is not included, so the slice returns 'el'. This is a fundamental string slicing behavior defined in Python's sequence protocol.
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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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