Community order is the valid walk

Lesson map

Lesson 13. Map, example, EX059.

flowchart TD
  V["valid, build order"] --> F{"Label is CLEAR or GREEN?"}
  F -->|Keep| P["GREEN domain, then the address"]
  F -->|Drop| A["AMBER skipped in between"]
  P --> Q{"Did CLEAR sort to the front?"}
  Q -->|No| K["Membership is not a sort"]

The pair ("TLP:CLEAR", "TLP:GREEN") is a membership test. It does not rank the rows.

Logical drawing

valid build order
  GREEN domain
  AMBER domain
  CLEAR address
community print
  donate-elmfield.example
  203.0.113.9
skipped between them
  elmfield-giftaid.example

Learning outcomes

After this chapter, you should be able to:

Read the community list from top to bottom.
Explain why the address is second.
Refuse a list that leads with CLEAR because of the label.

13.1 The filter keeps a value where `valid` put it. It does not regroup by label.

public walks valid and keeps a value when its label is in ("TLP:CLEAR", "TLP:GREEN"). That tuple is the set of allowed labels. Writing CLEAR before GREEN inside the tuple does not sort CLEAR items first. The walk order is the order pairs were appended. The GREEN domain was appended first. The AMBER domain was appended second and then dropped. The CLEAR address was appended third and kept. The printed list is therefore the domain, then 203.0.113.9.

Python prints that list with brackets and single quotes, after the literal shareable with community:. The brackets are the representation. They are not a TLP colour. A classmate who moves the address to the front "because CLEAR is the wider label" has applied a ranking the comprehension does not have. A classmate who puts the AMBER name back to fill the gap has undone the filter.

The invalid address never entered valid, so it cannot appear in this gap either. The gap is the dropped AMBER pair, not the rejected octet.

Lesson table; scroll horizontally to read all columns →

Position in `valid`	Community list
GREEN domain, first	Kept, first
AMBER domain, second	Dropped
CLEAR address, third	Kept, second
The invalid address	Never present

13.2 Worked example

Lesson table; scroll horizontally to read all columns →

Offered list	What the walk did	Decision
Domain, then `203.0.113.9`	Kept items in build order	Keep
AMBER absent from the middle	The label test	Keep
"CLEAR first, then GREEN."	The tuple is not a sort key	Refuse
"Insert the AMBER name where it was skipped."	The filter removed it	Refuse

Synthetic case. Two values are the whole community list.

Errors and limits

Do not reorder labels into a seriousness ranking.

Apply

EX059 — Filter order. Why does donate-elmfield.example print before 203.0.113.9, and why is the AMBER domain missing between them?
Show marking criteria
Rubric: 3 = the walk follows valid build order; CLEAR-before-GREEN in the test tuple is not a sort; AMBER fails the label test and leaves a gap; the invalid address was never in valid;; 2 = build order, and AMBER is filtered out;; 1 = one value;; 0 = none.