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13.13.3 Cursor Objects


13.13.3 Cursor Objects

A Cursor instance has the following attributes and methods:

execute( sql, [parameters])

Executes a SQL statement. The SQL statement may be parametrized (i. e. placeholders instead of SQL literals). The sqlite3 module supports two kinds of placeholders: question marks (qmark style) and named placeholders (named style).

This example shows how to use parameters with qmark style:

import sqlite3

con = sqlite3.connect("mydb")

cur = con.cursor()

who = "Yeltsin"
age = 72

cur.execute("select name_last, age from people where name_last=? and age=?", (who, age))
print cur.fetchone()

This example shows how to use the named style:

import sqlite3

con = sqlite3.connect("mydb")

cur = con.cursor()

who = "Yeltsin"
age = 72

cur.execute("select name_last, age from people where name_last=:who and age=:age",
    {"who": who, "age": age})
print cur.fetchone()

execute() will only execute a single SQL statement. If you try to execute more than one statement with it, it will raise a Warning. Use executescript() if you want to execute multiple SQL statements with one call.

executemany( sql, seq_of_parameters)
Executes a SQL command against all parameter sequences or mappings found in the sequence sql. The sqlite3 module also allows using an iterator yielding parameters instead of a sequence.

import sqlite3

class IterChars:
    def __init__(self):
        self.count = ord('a')

    def __iter__(self):
        return self

    def next(self):
        if self.count > ord('z'):
            raise StopIteration
        self.count += 1
        return (chr(self.count - 1),) # this is a 1-tuple

con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table characters(c)")

theIter = IterChars()
cur.executemany("insert into characters(c) values (?)", theIter)

cur.execute("select c from characters")
print cur.fetchall()

Here's a shorter example using a generator:

import sqlite3

def char_generator():
    import string
    for c in string.letters[:26]:
        yield (c,)

con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table characters(c)")

cur.executemany("insert into characters(c) values (?)", char_generator())

cur.execute("select c from characters")
print cur.fetchall()

executescript( sql_script)

This is a nonstandard convenience method for executing multiple SQL statements at once. It issues a COMMIT statement first, then executes the SQL script it gets as a parameter.

sql_script can be a bytestring or a Unicode string.

Example:

import sqlite3

con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.executescript("""
    create table person(
        firstname,
        lastname,
        age
    );

    create table book(
        title,
        author,
        published
    );

    insert into book(title, author, published)
    values (
        'Dirk Gently''s Holistic Detective Agency',
        'Douglas Adams',
        1987
    );
    """)

rowcount
Although the Cursor class of the sqlite3 module implements this attribute, the database engine's own support for the determination of "rows affected"/"rows selected" is quirky.

For SELECT statements, rowcount is always None because we cannot determine the number of rows a query produced until all rows were fetched.

For DELETE statements, SQLite reports rowcount as 0 if you make a DELETE FROM table without any condition.

For executemany statements, the number of modifications are summed up into rowcount.

As required by the Python DB API Spec, the rowcount attribute "is -1 in case no executeXX() has been performed on the cursor or the rowcount of the last operation is not determinable by the interface".

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