Python Database connection Close
Question:
Using the code below leaves me with an open connection, how do I close?
import pyodbc
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
csr = conn.cursor()
csr.close()
del csr
Answers:
Connections have a close method as specified in PEP-249 (Python Database API Specification v2.0):
import pyodbc
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
csr = conn.cursor()
csr.close()
conn.close() #<--- Close the connection
Since the pyodbc connection and cursor are both context managers, nowadays it would be more convenient (and preferable) to write this as:
import pyodbc
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
with conn:
crs = conn.cursor()
do_stuff
# conn.commit() will automatically be called when Python leaves the outer `with` statement
# Neither crs.close() nor conn.close() will be called upon leaving the `with` statement!!
See https://github.com/mkleehammer/pyodbc/issues/43 for an explanation for why conn.close() is not called.
Note that unlike the original code, this causes conn.commit() to be called. Use the outer with statement to control when you want commit to be called.
Also note that regardless of whether or not you use the with statements, per the docs,
Connections are automatically closed when they are deleted (typically when they go out of scope) so you should not normally need to call [conn.close()], but you can explicitly close the connection if you wish.
and similarly for cursors (my emphasis):
Cursors are closed automatically when they are deleted (typically when they go out of scope), so calling [csr.close()] is not usually necessary.
You might try turning off pooling, which is enabled by default. See this discussion for more information.
import pyodbc
pyodbc.pooling = False
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
csr = conn.cursor()
csr.close()
del csr
You can wrap the whole connection in a context manager, like the following:
from contextlib import contextmanager
import pyodbc
import sys
@contextmanager
def open_db_connection(connection_string, commit=False):
connection = pyodbc.connect(connection_string)
cursor = connection.cursor()
try:
yield cursor
except pyodbc.DatabaseError as err:
error, = err.args
sys.stderr.write(error.message)
cursor.execute("ROLLBACK")
raise err
else:
if commit:
cursor.execute("COMMIT")
else:
cursor.execute("ROLLBACK")
finally:
connection.close()
Then do something like this where ever you need a database connection:
with open_db_connection("...") as cursor:
# Your code here
The connection will close when you leave the with block. This will also rollback the transaction if an exception occurs or if you didn’t open the block using with open_db_connection("...", commit=True).
According to pyodbc documentation, connections to the SQL server are not closed by default. Some database drivers do not close connections when close() is called in order to save round-trips to the server.
To close your connection when you call close() you should set pooling to False:
import pyodbc
pyodbc.pooling = False
You can define a DB class as below. Also, as andrewf suggested, use a context manager for cursor access.I’d define it as a member function.
This way it keeps the connection open across multiple transactions from the app code and saves unnecessary reconnections to the server.
import pyodbc
class MS_DB():
""" Collection of helper methods to query the MS SQL Server database.
"""
def __init__(self, username, password, host, port=1433, initial_db='dev_db'):
self.username = username
self._password = password
self.host = host
self.port = str(port)
self.db = initial_db
conn_str = 'DRIVER=DRIVER=ODBC Driver 13 for SQL Server;SERVER='+
self.host + ';PORT='+ self.port +';DATABASE='+
self.db +';UID='+ self.username +';PWD='+
self._password +';'
print('Connected to DB:', conn_str)
self._connection = pyodbc.connect(conn_str)
pyodbc.pooling = False
def __repr__(self):
return f"MS-SQLServer('{self.username}', <password hidden>, '{self.host}', '{self.port}', '{self.db}')"
def __str__(self):
return f"MS-SQLServer Module for STP on {self.host}"
def __del__(self):
self._connection.close()
print("Connection closed.")
@contextmanager
def cursor(self, commit: bool = False):
"""
A context manager style of using a DB cursor for database operations.
This function should be used for any database queries or operations that
need to be done.
:param commit:
A boolean value that says whether to commit any database changes to the database. Defaults to False.
:type commit: bool
"""
cursor = self._connection.cursor()
try:
yield cursor
except pyodbc.DatabaseError as err:
print("DatabaseError {} ".format(err))
cursor.rollback()
raise err
else:
if commit:
cursor.commit()
finally:
cursor.close()
ms_db = MS_DB(username='my_user', password='my_secret', host='hostname')
with ms_db.cursor() as cursor:
cursor.execute("SELECT @@version;")
print(cur.fetchall())
The most common way to handle connections, if the language does not have a self closing construct like Using in .NET, then you should use a try -> finally to close the objects. Its possible that pyodbc does have some form of automatic closing but here is the code I do just in case:
conn = cursor = None
try:
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
cursor = conn.cursor()
# ... do stuff ...
finally:
try: cursor.close()
except: pass
try: conn.close()
except: pass
Using the code below leaves me with an open connection, how do I close?
import pyodbc
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
csr = conn.cursor()
csr.close()
del csr
Connections have a close method as specified in PEP-249 (Python Database API Specification v2.0):
import pyodbc
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
csr = conn.cursor()
csr.close()
conn.close() #<--- Close the connection
Since the pyodbc connection and cursor are both context managers, nowadays it would be more convenient (and preferable) to write this as:
import pyodbc
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
with conn:
crs = conn.cursor()
do_stuff
# conn.commit() will automatically be called when Python leaves the outer `with` statement
# Neither crs.close() nor conn.close() will be called upon leaving the `with` statement!!
See https://github.com/mkleehammer/pyodbc/issues/43 for an explanation for why conn.close() is not called.
Note that unlike the original code, this causes conn.commit() to be called. Use the outer with statement to control when you want commit to be called.
Also note that regardless of whether or not you use the with statements, per the docs,
Connections are automatically closed when they are deleted (typically when they go out of scope) so you should not normally need to call [
conn.close()], but you can explicitly close the connection if you wish.
and similarly for cursors (my emphasis):
Cursors are closed automatically when they are deleted (typically when they go out of scope), so calling [
csr.close()] is not usually necessary.
You might try turning off pooling, which is enabled by default. See this discussion for more information.
import pyodbc
pyodbc.pooling = False
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
csr = conn.cursor()
csr.close()
del csr
You can wrap the whole connection in a context manager, like the following:
from contextlib import contextmanager
import pyodbc
import sys
@contextmanager
def open_db_connection(connection_string, commit=False):
connection = pyodbc.connect(connection_string)
cursor = connection.cursor()
try:
yield cursor
except pyodbc.DatabaseError as err:
error, = err.args
sys.stderr.write(error.message)
cursor.execute("ROLLBACK")
raise err
else:
if commit:
cursor.execute("COMMIT")
else:
cursor.execute("ROLLBACK")
finally:
connection.close()
Then do something like this where ever you need a database connection:
with open_db_connection("...") as cursor:
# Your code here
The connection will close when you leave the with block. This will also rollback the transaction if an exception occurs or if you didn’t open the block using with open_db_connection("...", commit=True).
According to pyodbc documentation, connections to the SQL server are not closed by default. Some database drivers do not close connections when close() is called in order to save round-trips to the server.
To close your connection when you call close() you should set pooling to False:
import pyodbc
pyodbc.pooling = False
You can define a DB class as below. Also, as andrewf suggested, use a context manager for cursor access.I’d define it as a member function.
This way it keeps the connection open across multiple transactions from the app code and saves unnecessary reconnections to the server.
import pyodbc
class MS_DB():
""" Collection of helper methods to query the MS SQL Server database.
"""
def __init__(self, username, password, host, port=1433, initial_db='dev_db'):
self.username = username
self._password = password
self.host = host
self.port = str(port)
self.db = initial_db
conn_str = 'DRIVER=DRIVER=ODBC Driver 13 for SQL Server;SERVER='+
self.host + ';PORT='+ self.port +';DATABASE='+
self.db +';UID='+ self.username +';PWD='+
self._password +';'
print('Connected to DB:', conn_str)
self._connection = pyodbc.connect(conn_str)
pyodbc.pooling = False
def __repr__(self):
return f"MS-SQLServer('{self.username}', <password hidden>, '{self.host}', '{self.port}', '{self.db}')"
def __str__(self):
return f"MS-SQLServer Module for STP on {self.host}"
def __del__(self):
self._connection.close()
print("Connection closed.")
@contextmanager
def cursor(self, commit: bool = False):
"""
A context manager style of using a DB cursor for database operations.
This function should be used for any database queries or operations that
need to be done.
:param commit:
A boolean value that says whether to commit any database changes to the database. Defaults to False.
:type commit: bool
"""
cursor = self._connection.cursor()
try:
yield cursor
except pyodbc.DatabaseError as err:
print("DatabaseError {} ".format(err))
cursor.rollback()
raise err
else:
if commit:
cursor.commit()
finally:
cursor.close()
ms_db = MS_DB(username='my_user', password='my_secret', host='hostname')
with ms_db.cursor() as cursor:
cursor.execute("SELECT @@version;")
print(cur.fetchall())
The most common way to handle connections, if the language does not have a self closing construct like Using in .NET, then you should use a try -> finally to close the objects. Its possible that pyodbc does have some form of automatic closing but here is the code I do just in case:
conn = cursor = None
try:
conn = pyodbc.connect('DRIVER=MySQL ODBC 5.1 driver;SERVER=localhost;DATABASE=spt;UID=who;PWD=testest')
cursor = conn.cursor()
# ... do stuff ...
finally:
try: cursor.close()
except: pass
try: conn.close()
except: pass