Syllabus Lesson 2 of 141 · The blind start
The blind start

Baseline 1: one row per customer

AI off This is a baseline exam. The tutor is switched off and there are no hints. Work alone, the way you would with no assistant open. Nothing here is a trick: every rule is written in the exercise. Your result is only compared with your own final exam at the end of the course.

A shop is moving to a new system and wants one row per customer. Over the years the same person signed up from different devices, with capital letters, stray spaces and email tags. Some changed email but kept their name and postcode.

The worked example

1  Ada Okafor   ada.okafor@mail.com           N1 9GU
2  ADA  okafor   Ada.Okafor+news@Mail.com     n19gu
3  Ada Okafor   ada@work.org                  N1 9GU
4  A. Okafor    ADA@work.org                  E2 7RT
5  Tom Berg     (no email)                    SW1A 1AA
6  Sade Dube    (no email)                    M1 1AE
7  tom berg     tberg@mail.com                sw1a1aa
8  Tom Berg     tberg@mail.com                LS1 4AP
# -> [[1, 2, 3, 4], [5, 7, 8], [6]]
Your turn

Write merge_customers(records). Each record is a dict with "id" (a unique whole number), "name", "email" and "postcode". Return a list of groups, one per real customer; each group is a list of ids, and every id appears in exactly one group (a customer with no duplicates is a group of one). Order does not matter.

  • Email rule: two records are the same customer if their emails match after you trim spaces, lowercase, and drop a +tag from the part before @ (Ada.Okafor+news@Mail.com is ada.okafor@mail.com). An empty email matches nothing.
  • Name rule: they are also the same customer if their names match after lowercasing and collapsing spaces, and their postcodes match after removing spaces and uppercasing.
  • Chains: if A matches B and B matches C, all three are one customer, even if A and C share nothing.
Budget: on 1,400 records your code may run at most 200,000 steps (steps(), lines of your own code).

AI off: no tutor, hints or worked solution on this one. Your own thinking only.

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