Python Streaming Transform Script | Dataford Interview Questions

Write a Python script to parse, clean, and transform a large streaming dataset before loading it into a data warehouse.

Implement transform_stream(lines), which accepts a list of CSV line strings and returns a list of cleaned record dictionaries. Skip blank lines, the header user_id,event_time,amount, malformed rows, missing fields, negative amounts, and amounts with more than two decimal places. Strip whitespace, lowercase user_id, preserve the cleaned event_time, and convert valid amounts to integer cents. Use only the Python standard library.

Output

Return records in input order, each shaped as {"user_id": str, "event_time": str, "amount": int}.

Constraints

0 <= len(lines) <= 10^6
Each input element is a string representing one CSV line
Valid rows contain exactly three fields
Amounts must be nonnegative decimal values with at most two decimal places
The function must return a list in input order

Function Signature

def transform_stream(lines):

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