1 import sqlite3

Connecting SQLite to the Database

We use the functionsqlite3.connectto connect to the database. We can use the argument ":memory:" to create a temporary DB in the RAM or pass the name of a file to open or create it.

1 2 3 4 # Create a database in RAMdb =sqlite3.connect(':memory:')# Creates or opens a file called mydb with a SQLite3 DB 'data/mydb')

When we are done working with the DB we need to close the connection:

dbclose()

Creating (CREATE) and Deleting (DROP) Tables

In order to make any operation with the database we need to get a cursor object and pass the SQL statements to the cursor object to execute them. Finally it is necessary to commit the changes. We are going to create a users table with name,phone,email and password columns.

4 5 6 7 # Get a cursor objectcursor dbcursor)cursorexecute'''CREATE TABLE users(id INTEGER PRIMARY KEY,name TEXT, phone TEXT,email TEXT unique,password TEXT) ''')dbcommit)

To drop a table:

# Get a cursor object )cursor'''DROP TABLE users''')db)

Please note that the commit function is invoked on the db object,not the cursor object. If we typecursor.commitwe will getAttributeError: 'sqlite3.Cursor' object has no attribute 'commit'

Inserting (INSERT) Data into the Database

To insert data we use the cursor to execute the query. If you need values from Python variables it is recommended to use the "?" placeholder. Never use string operations or concatenation to make your queries because is very insecure. In this example we are going to insert two users in the database,their information is stored in python variables.

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 cursor)name1 'Andres'phone1'3366858'email1'user@example.com'# A very secure passwordpassword1'12345'name2'John'phone2'5557241'email2'johndoe@example.com'password2'abcdef'# Insert user 1cursor'''INSERT INTO users(name,email,password)VALUES(?,?,?)''', (name1phone1 email1 password1))print'First user inserted')# Insert user 2cursorname2phone2 email2 password2)'Second user inserted')db)

The values of the Python variables are passed inside a tuple. Another way to do this is passing a dictionary using the ":keyname" placeholder:

2 3 cursor{'name':name1'phone':phone1'email':email1'password':password1})

If you need to insert several users useexecutemanyand a list with the tuples:

4 5 users[(name3phone3 email3 password3] executemany''' INSERT INTO users(name,password) VALUES(?,224)!important"> users)db)

If you need to get the id of the row you just inserted uselastrowid:

2 id cursorlastrowid 'Last row id: %d'%id)

Retrieving Data (SELECT) with SQLite

To retrieve data,execute the query against the cursor object and then usefetchone()to retrieve a single row orfetchall()to retrieve all the rows.

cursor'''SELECT name,phone FROM users''')user1fetchone) #retrieve the first row(user1[0]#Print the first column retrieved(user's name)all_rowsfetchall)for row in all_rows:# row[0] returns the first column in the query (name),row[1] returns email column.'{0} : {1},{2}'.format(row row[1[2)

The cursor object works as an iterator,invokingfetchall()automatically:

cursor) cursor:

To retrive data with conditions,use again the "?" placeholder:

user_id 3 ( user_id ) user )

Updating (UPDATE) and Deleting (DELETE) Data

The procedure to update or delete data is the same as inserting data:

10 11 # Update user with id 1 newphone '3113093164' userid 1 '''UPDATE users SET phone = ? WHERE id = ? '''(newphone userid)# Delete user with id 2delete_userid 2cursor'''DELETE FROM users WHERE id = ? '''(delete_userid)db)

Using SQLite Transactions

Transactions are an useful property of database systems. It ensures the atomicity of the Database. Usecommitto save the changes:

cursordb#Commit the change

Orrollbackto roll back any change to the database since the last call tocommit:

cursor)# The user's phone is not updated rollback)

Please remember to always callcommitto save the changes. If you close the connection usingcloseor the connection to the file is lost (maybe the program finishes unexpectedly),not committed changes will be lost.

SQLite Database Exceptions

For best practices always surround the database operations with a try clause or a context manager:

8 9 18 19 sqlite3#Import the SQLite3 module try:# Creates or opens a file called mydb with a SQLite3 DBdb)# Get a cursor objectcursor)# Check if table users does not exist and create itcursor'''CREATE TABLE IF NOT EXISTSusers(id INTEGER PRIMARY KEY,phone TEXT,password TEXT)''') # Commit the changedb) # Catch the exceptionexceptException as e: # Roll back any change if something goes wrong)raise efinally: # Close the db connection)

In this example we used a try/except/finally clause to catch any exception in the code. Thefinallykeyword is very important because it always closes the database connection correctly. Please refer to thisarticleto find more about exceptions. Please take a look to:

# Catch the exception : e

This is called a catch-all clause,This is used here only as an example,in a real application you should catch a specific exception such asIntegrityErrororDatabaseError,for more information please refer toDB-API 2.0 Exceptions.

We can use the Connection object as context manager to automatically commit or rollback transactions:

14 name1'Andres'phone1'3366858'email1'user@example.com' # A very secure passwordpassword1'12345': with db:.IntegrityError: 'Record already exists'): )

In the example above if the insert statement raises an exception,the transaction will be rolled back and the message gets printed; otherwise the transaction will be committed. Please note that we callexecuteon thedbobject,not thecursorobject.

SQLite Row Factory and Data Types

The following table shows the relation between SQLite datatypes and Python datatypes:

• Nonetype is converted toNULL
• inttype is converted toINTEGER
• floattype is converted toREAL
• strtype is converted toTEXT
• bytestype is converted toBLOB

The row factory classsqlite3.Rowis used to access the columns of a query by name instead of by index:

8 db) .row_factoryRowcursor) ): # row['name'] returns the name column in the query,row['email'] returns email column.['name''email''phone') )

via:http://www.pythoncentral.io/introduction-to-sqlite-in-python/

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This article is part 1 of 2 in the seriesPython SQLite Tutorial Published: Thursday 11thApril 2013 Last Updated:Thursday 12 thDecember 2013 Share on facebook Share on google_plusone_share Share on twitter Share on stumbleupon Share on print Share on email SQLite3 is a very easy to use database engine. It is self-contained,serverless,zero-configuration and transactional. It is very fast and lightweight,and the entire database is stored in a single disk file. It is used in a lot of applications as internal data storage. The Python Standard Library includes a module called "sqlite3" intended for working with this database. This module is a SQL interface compliant with the DB-API 2.0 specification. Using Python's SQLite Module To use the SQLite3 module we need to add an import statement to our python script: