POC Data Management & Integration 3

Question 1

Which method in SQLAlchemy's ORM is used to add a new object to the session for insertion into the database?

Accepted Answer

session.add(obj)

Answer

session.add() stages a new ORM object for insertion; session.commit() then persists it to the database.

Question 2

What does the pandas 'groupby()' method return before an aggregation function is applied?

Accepted Answer

A GroupBy object

Answer

groupby() returns a DataFrameGroupBy or SeriesGroupBy object that holds groups and waits for an aggregation call like .sum() or .mean().

Question 3

Which Python standard library module is used to read and write JSON data?

Accepted Answer

json

Answer

The built-in json module provides json.loads(), json.dumps(), json.load(), and json.dump() for JSON serialization.

Question 4

In pandas, what is the result of performing an 'outer' merge when a key exists in only one DataFrame?

Accepted Answer

NaN is inserted for missing values from the other DataFrame

Answer

An outer merge keeps all rows from both DataFrames and fills missing counterpart values with NaN.

Question 5

Which method serializes a Python object to a JSON-formatted string?

Accepted Answer

json.dumps()

Answer

json.dumps() converts a Python object to a JSON string (the 's' suffix stands for 'string').

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