Manipulate data efficiently in Python
Role: Data Scientist
Category: Data Manipulation (SQL/Python)
Difficulty: medium
Interview Round: Onsite
Answer the following: (a) Contrast list comprehensions and generators with respect to memory and evaluation; write a generator that yields rolling windows of size k over a list. (b) In CPython 3.x, what is the maximum integer value and why? (c) Demonstrate a bug caused by Python’s pass-by-object-reference when mutating a list argument inside a function; fix it. (d) Given a pandas DataFrame of the events table (columns: user_id, event_date, event_type, revenue), compute per-country 7-day conversion on 2025-09-01 and total revenue using idiomatic groupby and boolean indexing; avoid apply for row-wise operations.
Quick Answer: This question evaluates proficiency in Python data manipulation, including memory and evaluation differences between list comprehensions and generators, CPython integer semantics, mutable argument behavior, and idiomatic pandas groupby and boolean indexing, and is commonly asked to assess performance awareness, understanding of language internals, debugging of mutable state, and practical data-aggregation skills. It belongs to the Data Manipulation (SQL/Python) domain and tests both conceptual understanding of language semantics and practical application of Python and pandas for efficient data processing.