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Course Library · Lesson 4 of 6
Digital · Guided lesson

Extract named fields

About 19 minutes · 4 reading + 15 practice and checks
Time includes reading, practice, and questions. Extra videos or further study are optional.
See this course’s project requirements

A checked extraction script for fictional equipment tags, dates and log lines, with a mismatch report and exact-match safety boundaries.

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • A precise tag grammar with four checked cases.
  • A segment-by-segment match explanation.
  • A whole-input validation rule with a counterexample.
  • An extracted log record with explicit string/number distinctions.
  • A semantic date check separate from regex matching.
  • A tested tag-and-log extraction tool with semantic limits.

Review and revise

Use these criteria to check your work and choose what to improve.

  • The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
  • Normal, boundary and rejected cases are recorded with expected versus observed results.
  • The changed case has a correct explanation and does not rely on hidden state.
  • The project includes source, outputs, instructions and honest tool, privacy and verification limits.
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Before you begin

The idea in everyday life

A log line is EQ-123 2026-02-28 ready. LINE captures tag, day, state; tag_number(EQ-007) returns integer 7 for calculation.

The idea

Named capture groups label parts of an accepted string. Preserve a textual identifier even when you convert its numeric portion; converting 007 to 7 loses padding that may matter to the external label.

Follow along

Extract named fields — original worked practice

Named capture groups label parts of an accepted string. Preserve a textual identifier even when you convert its numeric portion; converting 007 to 7 loses padding that may matter to the external label.

A log line is EQ-123 2026-02-28 ready. LINE captures tag, day, state; tag_number(EQ-007) returns integer 7 for calculation.

  1. 1. Step 1

    Read the three named groups.

    You should see: tag, day, state map to distinct fields.

    This keeps the rule and its observable result together.

  2. 2. Step 2

    Use groupdict on the complete match.

    You should see: Values are EQ-123,2026-02-28, ready.

    This keeps the rule and its observable result together.

  3. 3. Step 3

    Compare text 007 with integer 7.

    You should see: The text retains three-character padding; the integer does not.

    This keeps the rule and its observable result together.

  4. 4. Step 4

    Write a field dictionary with preserved tag text.

    You should see: An extracted log record with explicit string/number distinctions.

    This keeps the rule and its observable result together.

Now change one thing

Line state changes from ready to repair. Enter the extracted state word.

Your work

What to finish

An extracted log record with explicit string/number distinctions.

Common mistake

Watch for this

Depending on a group number after editing the pattern rather than using the declared field name.

How can I tell I understand it?

Explain and demonstrate the required distinction: Named capture groups label parts of an accepted string. Preserve a textual identifier even when you convert its numeric portion; converting 007 to 7 loses padding that may matter to the external label. Show a changed input and the expected result without weakening this contract.

Try 3 questions

Quick knowledge check

Answer all 3 questions. Get at least 2 right and the lesson completes automatically.

Not yet passed

You’ll get an explanation for each answer. Signed in? Your results save to your account.

1Which field holds 2026-02-28?
2What information is lost by converting 007 to integer 7?
3Why use groupdict?
0 of 3 answeredApply the lesson to a short question, then review the explanation.
4
Finish this lesson

Pass the check. We’ll save the progress.

Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.

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Sources and further reading

Explore the references behind this lesson.

docs.python.org — re.html
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

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