Python: sqlite3: List index out of range

Question

Hi i am looking for some help with an "List index out of range" error i am getting while trying to insert data into my sqlite3 database.

This is my first attempt at using a class helper to parse data to and from my database, so please don't laugh at my unwieldy coding. :))

here is my main.py for testing out my class.

import kivy
kivy.require('1.9.1')

from databaseHelper import DatabaseHelper
from kivy.app import App
from kivy.uix.widget import Widget  


class Window1(Widget):
    pass

class MyApp(App):
    def build(self):

        db = DatabaseHelper() 
        db.createDatabase('myDatabase')
        columnData = ['unix', 'value', 'datestamp', 'keyword']
        data = [57489543789, 2096, "12-12-12", "hello data"]

        db.createTable(db.name, "datatable", columnData)
        db.insertInto(db.name, "datatable", columnData, data)
        return Window1()


if __name__ == '__main__':
    MyApp().run()

Which creates the database and creates the table entries. Here is my insertInto method from my DatabaseHelper class.

def insertInto(self, db_name, table_name, column_data, data):
        self.db_name = db_name
        self.table_name = table_name
        self.column_data = column_data
        self.data = data

    try:
        conn = sqlite3.connect(self.db_name)
        c = conn.cursor()

        dataString = ''
        string = ''
        values = ''
        for i in data:
            string += column_data[i] + ", "
            values += '?, '
            dataString += 'self.data' + '[' + str(i) + ']' + ', '


        string = string[0:string.__len__() - 2]
        values = values[0:values.__len__() - 2]
        dataString = dataString[0:dataString.__len__() - 2]

        c.execute("INSERT INTO " + self.table_name + " (" + string + ")" + " VALUES " + "(" + values + ")",
                "(" + dataString + ")"                                                
                )
        conn.commit()
        print("Succesfully input data into database: " + self.db_name + " Table: " + self.table_name)

    except Exception as e:
        print("Failed to input data into database: " + self.db_name + " Table: " + self.table_name)
        print(e)

    finally:
        c.close()
        conn.close()

Which throws an "List index out of range" error.

Any help would be much appreciated, thanks.

Answer 1

There is way too much string manipulation going on there. This insertInto is probably closer to what you want:

def insertInto(self, db_name, table_name, column_data, data):
    self.db_name = db_name
    self.table_name = table_name
    self.column_data = column_data
    self.data = data

    try:
        conn = sqlite3.connect(self.db_name)
        c = conn.cursor()

        c.execute(
            "INSERT INTO {table} ({columns}) VALUES ({parameters})".format(
                table=table_name,
                columns=', '.join(column_data),
                parameters=', '.join(['?'] * len(column_data)),
            ),
            data
        )
        conn.commit()

        print("Succesfully input data into database: " + self.db_name + " Table: " + self.table_name)
    except Exception as e:
        print("Failed to input data into database: " + self.db_name + " Table: " + self.table_name)
        print(e)
    finally:
        c.close()
        conn.close()

The key changes here are:

• str.join ing all of the items instead of concatenating the next part and a delimiter in a loop, then slicing away the delimiter afterwards.

  Here's how it works:

   >>> ', '.join(['one', 'two', 'three']) 'one, two, three' 

• Using string formatting to build strings by naming parts instead of using the + operator a bunch. It's easier to read.

• Using list multiplication to get some number of ? placeholders.

  And here's how that works:

   >>> ['?'] * 5 ['?', '?', '?', '?', '?'] 

• Passing data as a parameter instead of a string with the text '(data[0], data[1], …)' . data should probably be a tuple, too:

   columnData = ('unix', 'value', 'datestamp', 'keyword') data = (57489543789, 2096, "12-12-12", "hello data") 

I'm also not sure what a DatabaseHelper is supposed to represent. Does it have any state associated with it? self.db_name , self.table_name , self.column_data , self.data … they all seem to get overwritten with every insertion. A database connection seems like useful state to associate with a database helper, though:

class DatabaseHelper:
    def __init__(self, db_name):
        self.connection = sqlite3.connect(self.db_name, isolation_level=None)

    def close(self):
        self.connection.close()

    def insertInto(self, table_name, columns, data):
        query = "INSERT INTO {table} ({columns}) VALUES ({parameters})".format(
            table=table_name,
            columns=', '.join(columns),
            parameters=', '.join(['?'] * len(columns))
        )

        self.connection.execute(query, data)

        print("Succesfully input data into database: " + db_name + " Table: " + table_name)

Then you can use it like this:

class MyApp(App):
    def build(self):
        db = DatabaseHelper('myDatabase')
        columnData = ('unix', 'value', 'datestamp', 'keyword')
        data = (57489543789, 2096, "12-12-12", "hello data")

        db.createTable("datatable", columnData)
        db.insertInto("datatable", columnData, data)
        return Window1()