Python Files and Small Programs: Exercises

Q1. Preserve the newline evidence

A UTF-8 file contains two lines. Its complete text is "north,18.5\nwest,24.0\n". Which value does file.read() return?

Choose one

One str containing both comma-separated rows and both newline characters.

A list containing the numbers 18.5 and 24.0.

Two strings with every newline removed automatically.

Select one choice, then check.

HintKeep reading separate from parsing

Ask what read() does before any call to split, strip, or float.

SolutionReturn the complete decoded string

file.read() returns "north,18.5\nwest,24.0\n". Parsing and numerical conversion are later operations.

Q2. Distinguish a path from its contents

What does Path("data") / "measurements.txt" produce before the program opens anything?

Choose one

A path value that describes a location; no file content has been read.

The decoded contents of measurements.txt.

A newly created empty text file.

Select one choice, then check.

HintLook for an input operation

The expression contains Path and /, but no open, read, or write.

SolutionName the location only

The expression produces a path value. The program must perform a separate file operation to learn whether the path exists or what it contains.

Q3. Compare characters and UTF-8 bytes

The label "café" has four characters. Its UTF-8 encoding contains the byte integers [99, 97, 102, 195, 169]. Which statement is correct?

Choose one

The text length is 4 and the encoded byte length is 5.

Both lengths are 5 because byte values determine character count.

Both lengths are 4 because every written character occupies one byte.

Select one choice, then check.

HintCount each sequence

str contains characters. bytes contains byte values.

SolutionKeep the two lengths separate

len("café") is 4, while the given encoded sequence has five byte values. The non-ASCII final character uses more than one UTF-8 byte.

Q4. Verify a strict binary round trip

Complete the program so it encodes the label with UTF-8, writes exact bytes, reads them back in binary mode, and decodes them to the original text.

Editable Python

HintMatch the mode to the value

encode produces bytes for wb. Reading with rb returns bytes for decode.

SolutionWrite and restore the same bytes

Q5. Preserve line identity while parsing

Complete the parser. It must report the invalid east reading with line number 2, keep the five valid labelled readings, and print their mean.

Editable Python

HintKeep the try block narrow

Preserve line_number and label outside the conversion. Put only reading = float(text) under try.

SolutionReport and skip at the input boundary

Q6. Choose replacement or append

Each run produces one complete current summary. A later run should replace the earlier summary. A separate audit log should retain one new line per run. Which mode pairing fits those meanings?

Choose one

Open the current summary with w and the audit log with a.

Open the current summary with a and the audit log with w.

Open both files with a so no earlier bytes are removed.

Select one choice, then check.

HintUse meaning, not habit

The summary should contain one report after every run. The log should keep earlier entries.

SolutionReplace the summary and extend the log

Use w for the generated summary and a for the audit log. The choice follows the result's contract.

Q7. Write and verify exact report text

Complete the write and read-back. A seeded older report must be replaced, and the saved text must match the intended report exactly.

Editable Python

HintVerify after closing the writer

Use one with block for writing and a later with block for reading.

SolutionRead back the completed write

Q8. Use path evidence before guessing

The runner expects data/measurements.txt, but input_path.is_file() is false. The output folder also does not exist. Which next step preserves the evidence?

Choose one

Print the working directory and resolved input path, reject missing input, and create only the output parent when writing a report.

Create an empty input file so the runner can continue without an error.

Replace the path with a guessed absolute location without inspecting the current working directory.

Select one choice, then check.

HintSeparate ownership

The program creates its generated report. Another source was expected to supply the measurements.

SolutionInspect input and create output deliberately

Use Path.cwd(), input_path.resolve(), and input_path.is_file() to locate the mismatch. Do not invent input. Create output_path.parent only before writing generated output.

Q9. Keep imported names traceable

Which description of these imports is correct?

Choose one

Counter is standard-library, parse_measurements is local, and np names an installed third-party module by its conventional alias.

All three names come from local files beside the runner.

The imports are wildcard imports because they bind names without a module prefix.

Select one choice, then check.

HintName the source of each import

Python ships collections; the project owns measurement_tools.py; NumPy is a separately installed library used later in the subject.

SolutionDistinguish the three origins

Counter comes from the standard library, parse_measurements from a local module, and np is the conventional local name for the third-party NumPy module.

Q10. Verify Counter and defaultdict against loops

Complete the standard-library count and grouping. Both results must equal the supplied manual dictionaries.

Editable Python

HintUse one tool for each established role

Counter consumes the full class sequence. A defaultdict with the list factory creates one group for a new sensor label.

SolutionKeep the equivalence visible

Q11. Assign one owner to each role

Which layout keeps supplied data, reusable functions, workflow, and generated output distinct without adding an unnecessary layer?

Choose one

data/measurements.txt, measurement_tools.py, run_report.py, and reports/summary.txt.

Put the input, generated report, and reusable functions together inside data/measurements.txt.

Create several empty helper modules before any separate responsibility exists.

Select one choice, then check.

HintGrow only for a real role

Four different responsibilities justify four clear destinations. Empty abstraction layers do not help the reader inspect the workflow.

SolutionUse the compact four-role layout

The first layout separates supplied input, reusable transformations, the runner, and generated output. It adds no file without a job.

Q12. Repair and rerun the complete workflow

The browser setup supplies data/measurements.txt, but the runner requests the wrong filename and appends its current report. Repair both defects. The same workflow must run twice, replace rather than duplicate the report, and verify the exact read-back on both runs.

Editable Python

HintPreserve supplied input and one current report

Change the requested filename to measurements.txt. Open the generated summary with w inside each run so the second result replaces the first.

SolutionRepair the path and output mode

Exercises

Read the Boundary

Q1. Preserve the newline evidence

Q2. Distinguish a path from its contents

Keep Text and Bytes Distinct

Q3. Compare characters and UTF-8 bytes

Q4. Verify a strict binary round trip

Editable Python

Parse and Report One Invalid Row

Q5. Preserve line identity while parsing

Editable Python

Write for the Result You Mean

Q6. Choose replacement or append

Q7. Write and verify exact report text

Editable Python

Diagnose Locations and Imports

Q8. Use path evidence before guessing

Q9. Keep imported names traceable

Reuse Understood Collection Work

Q10. Verify Counter and defaultdict against loops

Editable Python

Connect the Complete Program

Q11. Assign one owner to each role

Q12. Repair and rerun the complete workflow

Editable Python

Pause and reflect