This PCEP practice question tests your understanding of data types, variables, basic i/o and operators. 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 data scientist needs to read a list of floats from a file, one per line, and compute the sum. The current code:
total = 0.0
with open("data.txt") as f:
for line in f:total = total + line
print(total)
When run, a TypeError occurs: unsupported operand type(s) for +: 'float' and 'str'. The scientist knows that line is a string. Which fix will correctly sum the numbers?
Change to: total = total + eval(line)
Why wrong: eval is dangerous and not recommended.
Change to: total = total + line.strip()
Why wrong: This still tries to add a string to a float.
Change to: total = total + float(line.strip())
float() converts the string to a number.
Change to: total = total + int(line)
Why wrong: int() fails if the number has a decimal point.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Change to: total = total + float(line.strip())
Option C is correct because `float(line.strip())` converts the string read from the file (after removing any surrounding whitespace, including the newline character) into a float, which can then be added to the float variable `total`. The original error occurs because Python does not allow implicit addition of a string to a float.
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.
Change to: total = total + eval(line)
Why it's wrong here
eval is dangerous and not recommended.
Change to: total = total + line.strip()
Why it's wrong here
This still tries to add a string to a float.
Change to: total = total + float(line.strip())
Why this is correct
float() converts the string to a number.
Related concept
Read the scenario before looking for a memorised answer.
Change to: total = total + int(line)
Why it's wrong here
int() fails if the number has a decimal point.
Common exam traps
Python Institute often tests the candidate's understanding that file input is always a string and must be explicitly converted to a numeric type before arithmetic, and that `strip()` alone does not change the data type.
Detailed technical explanation
When reading a file line by line, each line is a string that includes the trailing newline character (`\n`). The `strip()` method removes this newline and any surrounding whitespace, leaving a clean string representation of the number. The `float()` constructor then parses that string into a floating-point number according to Python's numeric literal rules, allowing arithmetic operations. In real-world data pipelines, this pattern is common when processing CSV or log files where numeric values are stored as text.
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Data Types, Variables, Basic I/O and Operators — This question tests Data Types, Variables, Basic I/O and Operators — Read the scenario before looking for a memorised answer..
The correct answer is: Change to: total = total + float(line.strip()) — Option C is correct because `float(line.strip())` converts the string read from the file (after removing any surrounding whitespace, including the newline character) into a float, which can then be added to the float variable `total`. The original error occurs because Python does not allow implicit addition of a string to a float.
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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