## Chapter 5 — The source print follows the list ### Lesson map Lesson 05. Map, example, EX051. ```mermaid flowchart TD L["Four source tuples, written order"] --> D["deps grows by first sighting"] D --> P["Two dependency lines, then the independent line"] P --> Q{"Did a sort pick the inbox line?"} Q -->|No| K["Keep the embedded print"] ``` The walk follows `sources`. Nothing in the file sorts the names. ### Logical drawing ```text coordinator inbox: CCC alerts, Donation platform notices -> SINGLE POINT OF FAILURE form owner Sam: Volunteer reports -> SINGLE POINT OF FAILURE independent sources: ['National charity advisories'] ``` ### Learning outcomes After this chapter, you should be able to: 1. Name the order `sources` is written in. 2. Say why the inbox line prints before the form line. 3. Refuse a print that leads with the national advisories. ### 5.1 Keys appear when they are first needed. Names append after that. `lab_sources.py` stores four tuples. Each tuple is a source name, a channel, and a list of needs. The first tuple is CCC alerts, with the need `coordinator inbox`. The second is National charity advisories, with an empty needs list. The third is Donation platform notices, again needing `coordinator inbox`. The fourth is Volunteer reports, needing `form owner Sam`. The loop walks that written order. It never calls `sorted`. The mapping starts blank. A key opens at the earliest requirement. Alerts open the mailbox key. The donation-page record appends there, so the length is two. The shared-form record opens the other key alone. `items()` emits creation sequence. Mailbox comes before the other key. The web-page record adds no key. Its title sits at the bottom because a later statement prints it. A later decision to name a deputy is a sentence in the notes. It does not reorder these three lines. | What the walk uses | What it does not use | |---|---| | Position in `sources` | An alphabetical sort | | First sighting of a need | A severity score | | Append, for a repeated need | A staff directory | ### 5.2 Worked example | Offered result | What produced it | Decision | |---|---|---| | Inbox line, then form line, then the independent line | Insertion, then one extra print | Keep | | CCC alerts before Donation platform notices | Append order inside the inbox list | Keep | | "The script sorted by channel." | No sort is called | Refuse | | "National advisories print first because they are safest." | That tuple is not a `deps` key | Refuse | > **Synthetic case.** These three lines are the only source-lab output. ### Errors and limits Do not rebuild `sources` so that a preferred channel prints first. ### Apply - **EX051 — List order.** The print names the coordinator inbox, then form owner Sam, then the national advisories. May a preference for the independent source, or a later deputy, replace that order? *Rubric:* 3 = no; the dependency lines follow first sighting; names append in source order; the independent line is the last print; do not sort the script;; 2 = the three lines stay and the deputy stays prose;; 1 = one line;; 0 = none. ### Continue studying — lesson 05 (chapter 05 of 20) [← Chapter 04](#ch-04) · [Course chapter index](../SUBJECTS.md) · [Chapter 06 →](#ch-06) Continue to the next authored lesson. ## Worked answers **EX051.** No. The dependency lines follow first sighting, and names append in source order. The independent line is the last print. A later deputy does not reorder the script.