## Chapter 14 — vol-12 is a row the hits omit ### Lesson map Lesson 14. Map, example, EX060. ```mermaid flowchart TD R["Three mail rows"] --> H["Two hit tuples"] R --> M["vol-12 with news.example"] M --> Q{"Does the script print a MISS line?"} Q -->|No| K["Omission is the result"] ``` Three rows were written. Two qualified. The third stays in the source and off the hit list. ### Logical drawing ```text written in mail vol-07 vol-12 office printed under hits vol-07 office no line MISS: vol-12 ``` ### Learning outcomes After this chapter, you should be able to: 1. Count the mail rows and the hit tuples. 2. Name the omitted row. 3. Refuse a MISS line the script does not print. ### 14.1 The comprehension drops a non-member. It does not announce the drop. `mail` has three pairs. The comprehension keeps a pair only when the second field is in the valid set. `news.example` is not in that set, so vol-12 contributes nothing to `hits`. The printed list has two tuples. There is no third print that says the row was checked and missed. Absence from `hits` is the only trace of that check. vol-12 remains in the source list. Deleting the tuple to make the source "match the print" would destroy the evidence of a non-match. Adding `MISS: vol-12` would claim a column the file does not have. The row is also not a lookalike of a listed domain. It is a different name, `news.example`, and the equality test rejects it cleanly. The two labs stay apart here as well. `lab_sources.py` never sees vol-12, and `lab_rapid.py` never sees the coordinator inbox. A sentence that puts vol-12 on the source-dependency print has welded two files. | Row | In `hits`? | |---|---| | vol-07, listed domain | Yes | | vol-12, `news.example` | No, and no MISS line | | office, AMBER domain | Yes | | An invented miss column | Not in the file | ### 14.2 Worked example | Offered edit | Effect | Decision | |---|---|---| | "Leave vol-12 in the source and off the hit list." | The comprehension | Keep | | "Do not print MISS." | No such label | Keep | | "Delete vol-12 so the file shows only hits." | Loses the non-match | Refuse | | "The source lab also listed vol-12." | Different script | Refuse | > **Synthetic case.** vol-12 is a label in a three-row list. ### Errors and limits Do not fill the silence with a miss column. ### Apply - **EX060 — Omitted row.** What happened to vol-12, and does either lab print a MISS line? *Rubric:* 3 = vol-12 stays in mail with news.example; it is absent from hits because the value is not valid; neither script prints MISS; do not delete the row;; 2 = the row is a non-match and no MISS line exists;; 1 = the label only;; 0 = none. ### Continue studying — lesson 14 (chapter 14 of 20) [← Chapter 13](#ch-13) · [Course chapter index](../SUBJECTS.md) · [Chapter 15 →](#ch-15) Continue to the next authored lesson. ## Worked answers **EX060.** vol-12 stays in `mail` with `news.example`. It is absent from hits because that value is not valid. Neither script prints MISS. Do not delete the row.