## Chapter 8 — The independent line is a list repr ### Lesson map Lesson 08. Map, example, EX054. ```mermaid flowchart TD S["Four tuples"] --> E{"Is needs empty?"} E -->|Yes| L["One name in a Python list"] E -->|No| D["A deps key instead"] L --> P["Brackets and single quotes"] ``` Empty needs select the name. The print then shows Python's list form. ### Logical drawing ```text kept National charity advisories printed form ['National charity advisories'] excluded any tuple whose needs list is non-empty not shown the word web page ``` ### Learning outcomes After this chapter, you should be able to: 1. State the test `if not needs`. 2. Read the brackets and quotes as Python's list form. 3. Refuse a channel word the line does not contain. ### 8.1 Empty means independent. The brackets are part of the print. The last statement builds a list of names whose needs list is empty. `if not needs` is true for `[]` and false for a list that holds a string. Only National charity advisories has an empty needs list, so the result has one element. `print` of a list uses Python's representation: square brackets, a single-quoted string, and no extra label invented by Sam. The line begins with the words `independent sources:` because that literal is in the format string. The brackets are not a TLP mark. The channel `web page` is the second field of the tuple. The comprehension keeps `n` and drops the channel. A reader cannot recover `web page` from the independent line. The other three sources are absent here because each has a needs list, not because the script judged them unimportant. Fixing the inbox in prose does not move Donation platform notices onto this line. The embedded list still has one name. | Piece | What it contributes | |---|---| | `if not needs` | Selects an empty needs list | | List representation | Brackets and single quotes | | The channel field | Stored, not printed on this line | | A later shared mailbox | Does not edit the list | ### 8.2 Worked example | Offered reading | What the line shows | Decision | |---|---|---| | One name, inside brackets and quotes | The list representation | Keep | | The other three sources are absent | Their needs lists are non-empty | Keep | | "The line says web page." | The channel was not kept | Refuse | | "A shared mailbox removes the brackets." | The print is unchanged | Refuse | > **Synthetic case.** One independent name is the whole list. ### Errors and limits Do not treat the brackets as a sharing label. ### Apply - **EX054 — List form.** What does `['National charity advisories']` include, and why are the email sources absent from it? *Rubric:* 3 = one name in Python's list form; email sources have a non-empty needs list; the channel word is not on the line; a later mailbox fix does not edit the print;; 2 = the brackets hold one empty-needs name;; 1 = the name only;; 0 = none. ### Continue studying — lesson 08 (chapter 08 of 20) [← Chapter 07](#ch-07) · [Course chapter index](../SUBJECTS.md) · [Chapter 09 →](#ch-09) Continue to the next authored lesson. ## Worked answers **EX054.** The brackets hold one name, National charity advisories, because its needs list is empty. Email sources have a non-empty needs list. The channel word is not on the line, and a later mailbox fix does not edit the print.