Recursion Over Nested Data | Dataford Interview Questions

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Problem

Klaviyo event payloads can contain nested objects and arrays, such as profile properties, product details, and line items. Implement a recursive function that flattens a JSON-compatible payload into a dictionary of paths to scalar values.

Formal Specification

Given payload, a JSON-compatible Python dictionary or list, return a dictionary where:

Each scalar value, including strings, numbers, booleans, and None, becomes one output entry.
Nested dictionary keys are joined with ..
Array elements use zero-based numeric path components.
Empty dictionaries and lists produce no entries.
The input must not be modified.

For example, {"customer": {"email": "a@example.com"}} becomes {"customer.email": "a@example.com"}.

Constraints

1 <= number of contained values <= 10^4
Nesting depth is at most 100
Dictionary keys are non-empty strings and do not contain .
Values follow standard JSON types: object, array, string, number, boolean, or null

Function Signature

def flatten_event_payload(payload):