Module functions and constants¶
The pg
module defines a few functions that allow to connect
to a database and to define “default variables” that override
the environment variables used by PostgreSQL.
These “default variables” were designed to allow you to handle general
connection parameters without heavy code in your programs. You can prompt the
user for a value, put it in the default variable, and forget it, without
having to modify your environment. The support for default variables can be
disabled by setting the -DNO_DEF_VAR
option in the Python setup file.
Methods relative to this are specified by the tag [DV].
All variables are set to None
at module initialization, specifying that
standard environment variables should be used.
connect – Open a PostgreSQL connection¶
-
pg.
connect
([dbname][, host][, port][, opt][, tty][, user][, passwd])¶ Open a
pg
connectionParameters: - dbname – name of connected database (None =
defbase
) - host (str or None) – name of the server host (None =
defhost
) - port (int) – port used by the database server (-1 =
defport
) - opt (str or None) – connection options (None =
defopt
) - tty (str or None) – debug terminal (None =
deftty
) - user (str or None) – PostgreSQL user (None =
defuser
) - passwd (str or None) – password for user (None =
defpasswd
)
Returns: If successful, the
pgobject
handling the connectionReturn type: Raises: - TypeError – bad argument type, or too many arguments
- SyntaxError – duplicate argument definition
- pg.InternalError – some error occurred during pg connection definition
- Exception – (all exceptions relative to object allocation)
- dbname – name of connected database (None =
This function opens a connection to a specified database on a given PostgreSQL server. You can use keywords here, as described in the Python tutorial. The names of the keywords are the name of the parameters given in the syntax line. For a precise description of the parameters, please refer to the PostgreSQL user manual.
Example:
import pg
con1 = pg.connect('testdb', 'myhost', 5432, None, None, 'bob', None)
con2 = pg.connect(dbname='testdb', host='localhost', user='bob')
get/set_defhost – default server host [DV]¶
-
pg.
get_defhost
(host)¶ Get the default host
Returns: the current default host specification Return type: str or None Raises: TypeError – too many arguments
This method returns the current default host specification,
or None
if the environment variables should be used.
Environment variables won’t be looked up.
-
pg.
set_defhost
(host)¶ Set the default host
Parameters: host (str or None) – the new default host specification Returns: the previous default host specification Return type: str or None Raises: TypeError – bad argument type, or too many arguments
This methods sets the default host value for new connections.
If None
is supplied as parameter, environment variables will
be used in future connections. It returns the previous setting
for default host.
get/set_defport – default server port [DV]¶
-
pg.
get_defport
()¶ Get the default port
Returns: the current default port specification Return type: int Raises: TypeError – too many arguments
This method returns the current default port specification,
or None
if the environment variables should be used.
Environment variables won’t be looked up.
-
pg.
set_defport
(port)¶ Set the default port
Parameters: port (int) – the new default port Returns: previous default port specification Return type: int or None
This methods sets the default port value for new connections. If -1 is supplied as parameter, environment variables will be used in future connections. It returns the previous setting for default port.
get/set_defopt – default connection options [DV]¶
-
pg.
get_defopt
()¶ Get the default connection options
Returns: the current default options specification Return type: str or None Raises: TypeError – too many arguments
This method returns the current default connection options specification,
or None
if the environment variables should be used. Environment variables
won’t be looked up.
-
pg.
set_defopt
(options)¶ Set the default connection options
Parameters: options (str or None) – the new default connection options Returns: previous default options specification Return type: str or None Raises: TypeError – bad argument type, or too many arguments
This methods sets the default connection options value for new connections.
If None
is supplied as parameter, environment variables will be used in
future connections. It returns the previous setting for default options.
get/set_deftty – default debug tty [DV]¶
-
pg.
get_deftty
()¶ Get the default debug terminal
Returns: the current default debug terminal specification Return type: str or None Raises: TypeError – too many arguments
This method returns the current default debug terminal specification, or
None
if the environment variables should be used. Environment variables
won’t be looked up. Note that this is ignored in newer PostgreSQL versions.
-
pg.
set_deftty
(terminal)¶ Set the default debug terminal
Parameters: terminal (str or None) – the new default debug terminal Returns: the previous default debug terminal specification Return type: str or None Raises: TypeError – bad argument type, or too many arguments
This methods sets the default debug terminal value for new connections.
If None
is supplied as parameter, environment variables will be used
in future connections. It returns the previous setting for default terminal.
Note that this is ignored in newer PostgreSQL versions.
get/set_defbase – default database name [DV]¶
-
pg.
get_defbase
()¶ Get the default database name
Returns: the current default database name specification Return type: str or None Raises: TypeError – too many arguments
This method returns the current default database name specification, or
None
if the environment variables should be used. Environment variables
won’t be looked up.
-
pg.
set_defbase
(base)¶ Set the default database name
Parameters: base (str or None) – the new default base name Returns: the previous default database name specification Return type: str or None Raises: TypeError – bad argument type, or too many arguments
This method sets the default database name value for new connections. If
None
is supplied as parameter, environment variables will be used in
future connections. It returns the previous setting for default host.
get/set_defuser – default database user [DV]¶
-
pg.
get_defuser
()¶ Get the default database user
Returns: the current default database user specification Return type: str or None Raises: TypeError – too many arguments
This method returns the current default database user specification, or
None
if the environment variables should be used. Environment variables
won’t be looked up.
-
pg.
set_defuser
(user)¶ Set the default database user
Parameters: user – the new default database user Returns: the previous default database user specification Return type: str or None Raises: TypeError – bad argument type, or too many arguments
This method sets the default database user name for new connections. If
None
is supplied as parameter, environment variables will be used in
future connections. It returns the previous setting for default host.
get/set_defpasswd – default database password [DV]¶
-
pg.
get_defpasswd
()¶ Get the default database password
Returns: the current default database password specification Return type: str or None Raises: TypeError – too many arguments
This method returns the current default database password specification, or
None
if the environment variables should be used. Environment variables
won’t be looked up.
-
pg.
set_defpasswd
(passwd)¶ Set the default database password
Parameters: passwd – the new default database password Returns: the previous default database password specification Return type: str or None Raises: TypeError – bad argument type, or too many arguments
This method sets the default database password for new connections. If
None
is supplied as parameter, environment variables will be used in
future connections. It returns the previous setting for default host.
escape_string – escape a string for use within SQL¶
-
pg.
escape_string
(string)¶ Escape a string for use within SQL
Parameters: string (str) – the string that is to be escaped Returns: the escaped string Return type: str Raises: TypeError – bad argument type, or too many arguments
This function escapes a string for use within an SQL command.
This is useful when inserting data values as literal constants
in SQL commands. Certain characters (such as quotes and backslashes)
must be escaped to prevent them from being interpreted specially
by the SQL parser. escape_string()
performs this operation.
Note that there is also a pgobject
method with the same name
which takes connection properties into account.
Note
It is especially important to do proper escaping when handling strings that were received from an untrustworthy source. Otherwise there is a security risk: you are vulnerable to “SQL injection” attacks wherein unwanted SQL commands are fed to your database.
Example:
name = raw_input("Name? ")
phone = con.query("select phone from employees where name='%s'"
% escape_string(name)).getresult()
escape_bytea – escape binary data for use within SQL¶
-
pg.
escape_bytea
(datastring)¶ escape binary data for use within SQL as type
bytea
Parameters: datastring (str) – string containing the binary data that is to be escaped Returns: the escaped string Return type: str Raises: TypeError – bad argument type, or too many arguments
Escapes binary data for use within an SQL command with the type bytea
.
As with escape_string()
, this is only used when inserting data directly
into an SQL command string.
Note that there is also a pgobject
method with the same name
which takes connection properties into account.
Example:
picture = open('garfield.gif', 'rb').read()
con.query("update pictures set img='%s' where name='Garfield'"
% escape_bytea(picture))
unescape_bytea – unescape data that has been retrieved as text¶
-
pg.
unescape_bytea
(string)¶ Unescape
bytea
data that has been retrieved as textParameters: datastring (str) – the bytea
data string that has been retrieved as textReturns: byte string containing the binary data Return type: str Raises: TypeError – bad argument type, or too many arguments
Converts an escaped string representation of binary data into binary
data – the reverse of escape_bytea()
. This is needed when retrieving
bytea
data with one of the pgqueryobject.getresult()
,
pgqueryobject.dictresult()
or pgqueryobject.namedresult()
methods.
Example:
picture = unescape_bytea(con.query(
"select img from pictures where name='Garfield'").getresult[0][0])
open('garfield.gif', 'wb').write(picture)
get/set_decimal – decimal type to be used for numeric values¶
-
pg.
get_decimal
()¶ Get the decimal type to be used for numeric values
Returns: the Python class used for PostgreSQL numeric values Return type: class
This function returns the Python class that is used by PyGreSQL to hold
PostgreSQL numeric values. The default class is decimal.Decimal
if available, otherwise the float
type is used.
-
pg.
set_decimal
(cls)¶ Set a decimal type to be used for numeric values
Parameters: cls (class) – the Python class to be used for PostgreSQL numeric values
This function can be used to specify the Python class that shall
be used by PyGreSQL to hold PostgreSQL numeric values.
The default class is decimal.Decimal
if available,
otherwise the float
type is used.
get/set_decimal_point – decimal mark used for monetary values¶
-
pg.
get_decimal_point
()¶ Get the decimal mark used for monetary values
Returns: string with one character representing the decimal mark Return type: str
This function returns the decimal mark used by PyGreSQL to interpret
PostgreSQL monetary values when converting them to decimal numbers.
The default setting is '.'
as a decimal point. This setting is not
adapted automatically to the locale used by PostGreSQL, but you can
use set_decimal()
to set a different decimal mark manually. A return
value of None
means monetary values are not interpreted as decimal
numbers, but returned as strings including the formatting and currency.
New in version 4.1.1.
-
pg.
set_decimal_point
(string)¶ Specify which decimal mark is used for interpreting monetary values
Parameters: string (str) – string with one character representing the decimal mark
This function can be used to specify the decimal mark used by PyGreSQL
to interpret PostgreSQL monetary values. The default value is ‘.’ as
a decimal point. This value is not adapted automatically to the locale
used by PostGreSQL, so if you are dealing with a database set to a
locale that uses a ','
instead of '.'
as the decimal point,
then you need to call set_decimal(',')
to have PyGreSQL interpret
monetary values correctly. If you don’t want money values to be converted
to decimal numbers, then you can call set_decimal(None)
, which will
cause PyGreSQL to return monetary values as strings including their
formatting and currency.
New in version 4.1.1.
get/set_bool – whether boolean values are returned as bool objects¶
-
pg.
get_bool
()¶ Check whether boolean values are returned as bool objects
Returns: whether or not bool objects will be returned Return type: bool
This function checks whether PyGreSQL returns PostgreSQL boolean
values converted to Python bool objects, or as 'f'
and 't'
strings which are the values used internally by PostgreSQL. By default,
conversion to bool objects is not activated, but you can enable
this with the set_bool()
method.
New in version 4.2.
-
pg.
set_bool
(on)¶ Set whether boolean values are returned as bool objects
Parameters: on – whether or not bool objects shall be returned
This function can be used to specify whether PyGreSQL shall return
PostgreSQL boolean values converted to Python bool objects, or as
'f'
and 't'
strings which are the values used internally by PostgreSQL.
By default, conversion to bool objects is not activated, but you can
enable this by calling set_bool(True)
.
New in version 4.2.
get/set_namedresult – conversion to named tuples¶
-
pg.
get_namedresult
()¶ Get the function that converts to named tuples
This returns the function used by PyGreSQL to construct the result of the
pgqueryobject.namedresult()
method.
New in version 4.1.
-
pg.
set_namedresult
(func)¶ Set a function that will convert to named tuples
Parameters: func – the function to be used to convert results to named tuples
You can use this if you want to create different kinds of named tuples returned
by the pgqueryobject.namedresult()
method. If you set this function to
None, then it will become equal to pgqueryobject.getresult()
.
New in version 4.1.
Module constants¶
Some constants are defined in the module dictionary. They are intended to be used as parameters for methods calls. You should refer to the libpq description in the PostgreSQL user manual for more information about them. These constants are:
-
version, __version__
constants that give the current version
-
INV_READ, INV_WRITE
large objects access modes, used by
pgobject.locreate()
andpglarge.open()
-
SEEK_SET, SEEK_CUR, SEEK_END:
positional flags, used by
pglarge.seek()