If we try to call connect() on an already-open database, we get a OperationalError:

>>> db.connect()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/charles/pypath/peewee.py", line 2390, in connect
    raise OperationalError('Connection already opened.')
peewee.OperationalError: Connection already opened.

To prevent this exception from being raised, we can call connect() with an additional argument, reuse_if_open:

>>> db.close()  # Close connection.
True
True
>>> db.connect(reuse_if_open=True)
False

Note that the call to connect() returns if the database connection was already open.

To close a connection, use the method:

>>> db.connect()  # Open connection.
True
>>> db.close()  # Close connection.
True
>>> db.close()  # Connection already closed, returns False.
False

You can test whether the database is closed using the Database.is_closed() method:

>>> db.is_closed()
True

It is not necessary to explicitly connect to the database before using it if the database is initialized with autoconnect=True (the default). Managing connections explicitly is considered a best practice, therefore you may consider disabling the autoconnect behavior.

It is very helpful to be explicit about your connection lifetimes. If the connection fails, for instance, the exception will be caught when the connection is being opened, rather than some arbitrary time later when a query is executed. Furthermore, if using a , it is necessary to call connect() and to ensure connections are recycled properly.

For the best guarantee of correctness, disable autoconnect:

The database object itself can be used as a context-manager, which opens a connection for the duration of the wrapped block of code. Additionally, a transaction is opened at the start of the wrapped block and committed before the connection is closed (unless an error occurs, in which case the transaction is rolled back).

>>> db.is_closed()
>>> with db:
...     print(db.is_closed())  # db is open inside context manager.
...
False
>>> db.is_closed()  # db is closed.
True

If you want to manage transactions separately, you can use the Database.connection_context() context manager.

>>> with db.connection_context():
...     # db connection is open.
...     pass
...
>>> db.is_closed()  # db connection is closed.
True

The connection_context() method can also be used as a decorator:

To obtain a reference to the underlying DB-API 2.0 connection, use the method. This method will return the currently-open connection object, if one exists, otherwise it will open a new connection.

<sqlite3.Connection object at 0x7f94e9362f10>