Measure whether the project virtualenv works

Translate the claim into assertions or a tiny eval harness. The metric to protect is: which python points inside .venv; importlib.metadata.version('pandas') matches pin. Always record the denominator (how many cases) beside any rate. A percentage without a denominator is marketing, not measurement.

source .venv/bin/activate
python -c "import sys; assert '.venv' in sys.prefix; import pandas; print(sys.prefix)"

Expected evidence: sys.prefix contains .venv. A passing assertion proves only the behavior it names; broader usefulness still needs the chapter’s full limits.

Be explicit: beating the baseline (record global site-packages pandas version (or absence) before creating the venv) on this fixture does not prove behavior under pip installing into the system Python, or activating the wrong venv. Label observations separately from conclusions so the next page inherits honest evidence about the project virtualenv.

Compute which python points inside .venv; importlib.metadata.version('pandas') matches pin with the denominator written beside the rate every time. For this chapter, the evaluation set is intentionally tiny; that is allowed only if you say so in the evidence. Compare against record global site-packages pandas version (or absence) before creating the venv before celebrating.

Add one negative case aimed at pip installing into the system Python, or activating the wrong venv. A suite with only happy cases cannot protect the project virtualenv when the characteristic failure appears in review.

If a check is expensive or flaky, shrink it until it is deterministic on project dir lab-env/ with requirements.txt containing pandas==2.2.2. Flaky green builds teach the team to ignore gates. Record what this page does not prove so security-ops and mastery-ship inherit honest limits.

At the evaluation stage for python-virtual-environments, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about project dir lab-env/ with requirements.txt containing pandas==2.2.2 that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: record global site-packages pandas version (or absence) before creating the venv.

For this page specifically, success looks like metrics with explicit denominators and a negative case while still centering the user decision to install project packages without mutating the global interpreter. If you cannot point to a file, command, or assertion that proves that for the project virtualenv, stay on this page instead of advancing.

Set up a virtual environment

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Return to the python virtual environments scenario and restate what this chapter proved on page validation.mdx. Name one metric, one ownership rule, and one regression test you will keep. Explain how this page connects to the previous page without repeating earlier paragraphs. If you cannot name a falsifier, the chapter is still a story rather than a controlled practice. Write the falsifier as an observable event with a threshold.

Return to the python virtual environments scenario and restate what this chapter proved on page validation.mdx. Name one metric, one ownership rule, and one regression test you will keep. Explain how this page connects to the previous page without repeating earlier paragraphs. If you cannot name a falsifier, the chapter is still a story rather than a controlled practice. Write the falsifier as an observable event with a threshold.