Floating Point and Money

Trial I, The Sirens. The answer that sounds right.

The Sirens sang a song every sailor recognised, and the ships that steered toward it broke on the rocks. Odysseus had himself tied to the mast so he could hear it without acting on it. Python has songs like that: answers so obviously right that nobody checks them. This trial ties you to the mast.

Time: About 35 min
Python: Standard library
To clear: 12 of 17 points
Laurel: All 22 points

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Leg I of 8, Troy to Ithaca

What you will do

1Why some fractions never end
2The PnL that should be zeroPredict, then run · 4 points
3Look inside a doubleExplore · 4 points
4Rounding you thought you knewPredict, then run · 4 points
5Why this matters on a deskDesk context
6Fix the reconciliation that cries wolfFix the code · 5 points
7Harder variant: allocate to the pennyWrite the code · 5 points · optional
8What to carry out of this stageDesk context

What clearing it proves

Compare two books of amounts without generating false reconciliation breaks.

IEEE 754 intuition
tolerance comparison
minor units
reconciliation logic

Part of Production Python for Finance. Grading is deterministic and runs on the server.