How to interpret this strange Python routine coding format

Question

I came across a strange format of Python code about routine. What is the actual meaning?

def get_values() -> list:
    query = "select value from table"
    result = db.execute(query)
    return [ value[0] for value in result ]

I think the -> list means this routine returns data type list but I don't understand how the return (build a list)? Why it is value[0]?

Answer 1

If you are using sqlite3 (guessing) execute() returns a <sqlite3.Cursor> an iterable containing the tuples satisfying the conditions of your query.

Something like

('2006-01-05', 'BUY', 'RHAT', 100, 35.14)
('2006-03-28', 'BUY', 'IBM', 1000, 45.0)
('2006-04-06', 'SELL', 'IBM', 500, 53.0)
('2006-04-05', 'BUY', 'MSFT', 1000, 72.0)
...

Then

[value[0] for value in result]

creates a list of all the first columns in result.

['2006-01-05', '2006-03-28', '2006-04-06', '2006-04-05', ...]