Python - Instantiate object from SQLite cursor

Question

I'm running into an error when I try to instantiate an object from a cursor in SQLite and I've exhausted my research and couldn't find a solution.

Premise: I cannot use SqlAlchemy or anything of that sorts.

Assumption: The database (SQLite) works, it contains a table named table_cars, and the table is populated with data in its single column: name.

So, I have a class lets say:

class Car():
   def __init__(self, name):
      self.name = name

   @classmethod
      def from_cursor(cls, c):
         car = cls(c(0))
         # this line breaks when called from the function below.

And I also have a db module, with the following function:

def get_cars_from_db():
   sql = 'SELECT * FROM table_cars;'
   conn = get_conn()
   cur = conn.cursor()
   cur.execute(sql)
   data = cur.fetchall()
   # at this point, if i print the cursor, I can see all data, so far so good.

   cars = [Car.from_cursor(c) for c in data]
   # the line above causes the code to break

   return cars

The code breaks with the following error:

TypeError: 'tuple' object is not callable

What am I doing wrong here?

In list comprehension of get_cars_from_db(), c is a row of the db select result. In from_cursor() you are using c(0) which means c is callable and you are calling it with parameter 0 — kuro
– kuro, Commented May 26, 2021 at 12:35
so how do I extract the data from the cursor to parse it into the object? — Rodrigo Bastos
– Rodrigo Bastos, Commented May 26, 2021 at 12:37
In from_cursor(), c is a tuple with same number of entries as column in your table_cars. You can fetch the name from that tuple and then create Car object — kuro
– kuro, Commented May 26, 2021 at 12:40
now I realise that I need to use [] to access an index of a tuple, not (). Silly me. so the correct syntax would be car = cls(c[0]) — Rodrigo Bastos
– Rodrigo Bastos, Commented May 26, 2021 at 12:44

Alexander Volkovsky · Accepted Answer · 2021-05-26 12:49:40Z

2

You can use cls(c[0]) or cls(*c) to unpack tuple to function arguments. It's also worth to specify an exact order of your columns in query.

select name from table_cars

answered May 26, 2021 at 12:49

Alexander Volkovsky

2,9681 gold badge12 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Python - Instantiate object from SQLite cursor

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related