1. DATABASES in Python with dbm module¶
Python provides a database API that is very useful when needed to work with different type of databases. The data are stored within a DBM (database manager) persistent dictionaries that work like normal Python dictionaries except that the data is written to and read from disk.
There are many DBM modules that are unfortunately not compatible. Amongst them, the anydbm module offers an alternative to choose the best DBM module available. Except if you need a very specific feature of another DBM module, use the anydbm module.
1.1. Quickstart with DBM¶
The following example illustrates the use of a DBM module that is used to store data into a DB using dictionary-like syntax.:
>>> import anydbm >>> # open a DB. The c option opens in read/write mode and creates the file if needed. >>> db = anydbm.open('websites', 'c') >>> # add an item >>> db["item1"] = "First example" >>> print db['item1'] "First example" >>> # close and save >>> db.close()
the key and value of each entry must be a string
Python supports any DBM (database manager) and a similar interface. The main difference lies in the underrlying format. The database is a persistent dictionaries that work like normal Python dictionaries except that the data is written to and read from disk.
Amongst the different DBM, the anydbm module offers an alternative to choose the best DBM module available. If you need a very specific feature of another DBM module, use the anydbm module.
The DBM modules work when your data needs can be stored as key/value pairs. You can use such DBM persistent dictionary when :
- data needs are simple
- small amount of data
- if you require support for transactions (when more than one thing happens at once), use a relational database
1.2. Relational databases¶
we assume that you know SQL commands.
There are several databases possible. We will use sqlite3:
>>> import sqlite3 >>> conn = sqlite3.connect("example.db") >>> c = conn.cursor() >>> c.execute('create table Persons (id int, name text, city text)') >>> c.execute('insert into Persons VALUES (1, "smith", "dallas")') >>> conn.commit() >>> conn.close() >>> import sqlite3 >>> conn = sqlite3.connect('example.db') >>> c = conn.cursor() >>> x = c.execute("select * from Persons") >>> x.fetchall() [(1, u'smith', u'dallas')]
now fetchall is empty. You need to execute a command again
Not a standard python module. Not tested
import MySQLdb connection = MySQLdb.connect(host="localhost", db="Student", port=8000, username="laura", passwd="password") conn = connection.cursor() conn.execute('create table Login (user char(20),password char(20))') conn.execute('insert into Login values("user1","passwd2")') results = conn.execute('select * from Login') results.fetchone() results.fetchall()
x.arraysize x.fetchmany x.row_factory x.executemany x.rowcount x.executescript x.lastrowid x.setinputsizes x.description x.setoutputsize
connection using connect
conn.DataError conn.create_function conn.DatabaseError conn.cursor conn.Error conn.execute con.IntegrityError conn.executemany conn.InterfaceError conn.executescript conn.InternalError conn.interrupt conn.NotSupportedError conn.isolation_level conn.OperationalError conn.iterdump conn.ProgrammingError conn.rollback conn.Warning conn.row_factory conn.close conn.set_authorizer conn.commit conn.set_progress_handler conn.create_aggregate conn.text_factory conn.create_collation conn.total_changes