ydb/contrib/python/pg8000/README.md

pg8000

pg8000 is a pure-Python PostgreSQL driver that complies with DB-API 2.0. It is tested on Python versions 3.8+, on CPython and PyPy, and PostgreSQL versions 12+. pg8000's name comes from the belief that it is probably about the 8000th PostgreSQL interface for Python. pg8000 is distributed under the BSD 3-clause license.

All bug reports, feature requests and contributions are welcome at http://github.com/tlocke/pg8000/.

Installation

To install pg8000 using pip type: pip install pg8000

Native API Interactive Examples

pg8000 comes with two APIs, the native pg8000 API and the DB-API 2.0 standard API. These are the examples for the native API, and the DB-API 2.0 examples follow in the next section.

Basic Example

Import pg8000, connect to the database, create a table, add some rows and then query the table:

>>> import pg8000.native
>>>
>>> # Connect to the database with user name postgres
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> # Create a temporary table
>>>
>>> con.run("CREATE TEMPORARY TABLE book (id SERIAL, title TEXT)")
>>>
>>> # Populate the table
>>>
>>> for title in ("Ender's Game", "The Magus"):
...     con.run("INSERT INTO book (title) VALUES (:title)", title=title)
>>>
>>> # Print all the rows in the table
>>>
>>> for row in con.run("SELECT * FROM book"):
...     print(row)
[1, "Ender's Game"]
[2, 'The Magus']
>>>
>>> con.close()

Transactions

Here's how to run groups of SQL statements in a transaction:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("START TRANSACTION")
>>>
>>> # Create a temporary table
>>> con.run("CREATE TEMPORARY TABLE book (id SERIAL, title TEXT)")
>>>
>>> for title in ("Ender's Game", "The Magus", "Phineas Finn"):
...     con.run("INSERT INTO book (title) VALUES (:title)", title=title)
>>> con.run("COMMIT")
>>> for row in con.run("SELECT * FROM book"):
...     print(row)
[1, "Ender's Game"]
[2, 'The Magus']
[3, 'Phineas Finn']
>>>
>>> con.close()

rolling back a transaction:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> # Create a temporary table
>>> con.run("CREATE TEMPORARY TABLE book (id SERIAL, title TEXT)")
>>>
>>> for title in ("Ender's Game", "The Magus", "Phineas Finn"):
...     con.run("INSERT INTO book (title) VALUES (:title)", title=title)
>>>
>>> con.run("START TRANSACTION")
>>> con.run("DELETE FROM book WHERE title = :title", title="Phineas Finn") 
>>> con.run("ROLLBACK")
>>> for row in con.run("SELECT * FROM book"):
...     print(row)
[1, "Ender's Game"]
[2, 'The Magus']
[3, 'Phineas Finn']
>>>
>>> con.close()

NB. There is a longstanding bug in the PostgreSQL server whereby if a COMMIT is issued against a failed transaction, the transaction is silently rolled back, rather than an error being returned. pg8000 attempts to detect when this has happened and raise an InterfaceError.

Query Using Functions

Another query, using some PostgreSQL functions:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT TO_CHAR(TIMESTAMP '2021-10-10', 'YYYY BC')")
[['2021 AD']]
>>>
>>> con.close()

Interval Type

A query that returns the PostgreSQL interval type:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> import datetime
>>>
>>> ts = datetime.date(1980, 4, 27)
>>> con.run("SELECT timestamp '2013-12-01 16:06' - :ts", ts=ts)
[[datetime.timedelta(days=12271, seconds=57960)]]
>>>
>>> con.close()

Point Type

A round-trip with a PostgreSQL point type:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT CAST(:pt as point)", pt=(2.3,1))
[[(2.3, 1.0)]]
>>>
>>> con.close()

Client Encoding

When communicating with the server, pg8000 uses the character set that the server asks it to use (the client encoding). By default the client encoding is the database's character set (chosen when the database is created), but the client encoding can be changed in a number of ways (eg. setting CLIENT_ENCODING in postgresql.conf). Another way of changing the client encoding is by using an SQL command. For example:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SET CLIENT_ENCODING TO 'UTF8'")
>>> con.run("SHOW CLIENT_ENCODING")
[['UTF8']]
>>>
>>> con.close()

JSON

JSON always comes back from the server de-serialized. If the JSON you want to send is a dict then you can just do:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> val = {'name': 'Apollo 11 Cave', 'zebra': True, 'age': 26.003}
>>> con.run("SELECT CAST(:apollo as jsonb)", apollo=val)
[[{'age': 26.003, 'name': 'Apollo 11 Cave', 'zebra': True}]]
>>>
>>> con.close()

JSON can always be sent in serialized form to the server:

>>> import json
>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>>
>>> val = ['Apollo 11 Cave', True, 26.003]
>>> con.run("SELECT CAST(:apollo as jsonb)", apollo=json.dumps(val))
[[['Apollo 11 Cave', True, 26.003]]]
>>>
>>> con.close()

JSON queries can be have parameters:

>>> import pg8000.native
>>>
>>> with pg8000.native.Connection("postgres", password="cpsnow") as con:
...     con.run(""" SELECT CAST('{"a":1, "b":2}' AS jsonb) @> :v """, v={"b": 2})
[[True]]

Retrieve Column Metadata From Results

Find the column metadata returned from a query:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("create temporary table quark (id serial, name text)")
>>> for name in ('Up', 'Down'):
...     con.run("INSERT INTO quark (name) VALUES (:name)", name=name)
>>> # Now execute the query
>>>
>>> con.run("SELECT * FROM quark")
[[1, 'Up'], [2, 'Down']]
>>>
>>> # and retrieve the metadata
>>>
>>> con.columns
[{'table_oid': ..., 'column_attrnum': 1, 'type_oid': 23, 'type_size': 4, 'type_modifier': -1, 'format': 0, 'name': 'id'}, {'table_oid': ..., 'column_attrnum': 2, 'type_oid': 25, 'type_size': -1, 'type_modifier': -1, 'format': 0, 'name': 'name'}]
>>>
>>> # Show just the column names
>>>
>>> [c['name'] for c in con.columns]
['id', 'name']
>>>
>>> con.close()

Notices And Notifications

PostgreSQL notices are stored in a deque called Connection.notices and added using the append() method. Similarly there are Connection.notifications for notifications . Here's an example:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("LISTEN aliens_landed")
>>> con.run("NOTIFY aliens_landed")
>>> # A notification is a tuple containing (backend_pid, channel, payload)
>>>
>>> con.notifications[0]
(..., 'aliens_landed', '')
>>>
>>> con.close()

Parameter Statuses

Certain parameter values are reported by the server automatically at connection startup or whenever their values change and pg8000 stores the latest values in a dict called Connection.parameter_statuses. Here's an example where we set the aplication_name parameter and then read it from the parameter_statuses:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection(
...     "postgres", password="cpsnow", application_name='AGI')
>>>
>>> con.parameter_statuses['application_name']
'AGI'
>>>
>>> con.close()

LIMIT ALL

You might think that the following would work, but in fact it fails:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT 'silo 1' LIMIT :lim", lim='ALL')
Traceback (most recent call last):
pg8000.exceptions.DatabaseError: ...
>>>
>>> con.close()

Instead the docs say that you can send null as an alternative to ALL, which does work:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT 'silo 1' LIMIT :lim", lim=None)
[['silo 1']]
>>>
>>> con.close()

IN and NOT IN

You might think that the following would work, but in fact the server doesn't like it:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT 'silo 1' WHERE 'a' IN :v", v=['a', 'b'])
Traceback (most recent call last):
pg8000.exceptions.DatabaseError: ...
>>>
>>> con.close()

the most straightforward way to get around this problem is to rewrie the query using the ANY function:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT 'silo 1' WHERE 'a' = ANY(:v)", v=['a', 'b'])
[['silo 1']]
>>> con.close()

However, using the array variant of ANY may cause a performance problem and so you can use the subquery variant of IN with the unnest function:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run(
...     "SELECT 'silo 1' WHERE 'a' IN (SELECT unnest(CAST(:v as varchar[])))",
...     v=['a', 'b'])
[['silo 1']]
>>> con.close()

and you can do the same for NOT IN.

Many SQL Statements Can't Be Parameterized

In PostgreSQL parameters can only be used for data values, not identifiers . Sometimes this might not work as expected, for example the following fails:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> channel = 'top_secret'
>>>
>>> con.run("LISTEN :channel", channel=channel)
Traceback (most recent call last):
pg8000.exceptions.DatabaseError: ...
>>>
>>> con.close()

It fails because the PostgreSQL server doesn't allow this statement to have any parameters. There are many SQL statements that one might think would have parameters, but don't. For these cases the SQL has to be created manually, being careful to use the identifier() and literal() functions to escape the values to avoid SQL injection attacks:

>>> from pg8000.native import Connection, identifier, literal
>>>
>>> con = Connection("postgres", password="cpsnow")
>>>
>>> channel = 'top_secret'
>>> payload = 'Aliens Landed!'
>>> con.run(f"LISTEN {identifier(channel)}")
>>> con.run(f"NOTIFY {identifier(channel)}, {literal(payload)}")
>>>
>>> con.notifications[0]
(..., 'top_secret', 'Aliens Landed!')
>>>
>>> con.close()

COPY FROM And TO A Stream

The SQL COPY statement can be used to copy from and to a file or file-like object. Here's an example using the CSV format:

>>> import pg8000.native
>>> from io import StringIO
>>> import csv
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> # Create a CSV file in memory
>>>
>>> stream_in = StringIO()
>>> csv_writer = csv.writer(stream_in)
>>> csv_writer.writerow([1, "electron"])
12
>>> csv_writer.writerow([2, "muon"])
8
>>> csv_writer.writerow([3, "tau"])
7
>>> stream_in.seek(0)
0
>>>
>>> # Create a table and then copy the CSV into it
>>>
>>> con.run("CREATE TEMPORARY TABLE lepton (id SERIAL, name TEXT)")
>>> con.run("COPY lepton FROM STDIN WITH (FORMAT CSV)", stream=stream_in)
>>>
>>> # COPY from a table to a stream
>>>
>>> stream_out = StringIO()
>>> con.run("COPY lepton TO STDOUT WITH (FORMAT CSV)", stream=stream_out)
>>> stream_out.seek(0)
0
>>> for row in csv.reader(stream_out):
...     print(row)
['1', 'electron']
['2', 'muon']
['3', 'tau']
>>>
>>> con.close()

It's also possible to COPY FROM an iterable, which is useful if you're creating rows programmatically:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> # Generator function for creating rows
>>> def row_gen():
...     for i, name in ((1, "electron"), (2, "muon"), (3, "tau")):
...         yield f"{i},{name}\n"
>>>
>>> # Create a table and then copy the CSV into it
>>>
>>> con.run("CREATE TEMPORARY TABLE lepton (id SERIAL, name TEXT)")
>>> con.run("COPY lepton FROM STDIN WITH (FORMAT CSV)", stream=row_gen())
>>>
>>> # COPY from a table to a stream
>>>
>>> stream_out = StringIO()
>>> con.run("COPY lepton TO STDOUT WITH (FORMAT CSV)", stream=stream_out)
>>> stream_out.seek(0)
0
>>> for row in csv.reader(stream_out):
...     print(row)
['1', 'electron']
['2', 'muon']
['3', 'tau']
>>>
>>> con.close()

Execute Multiple SQL Statements

If you want to execute a series of SQL statements (eg. an .sql file), you can run them as expected:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> statements = "SELECT 5; SELECT 'Erich Fromm';"
>>>
>>> con.run(statements)
[[5], ['Erich Fromm']]
>>>
>>> con.close()

The only caveat is that when executing multiple statements you can't have any parameters.

Quoted Identifiers in SQL

Say you had a column called My Column. Since it's case sensitive and contains a space, you'd have to surround it by double quotes . But you can't do:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("select 'hello' as "My Column"")
Traceback (most recent call last):
SyntaxError: invalid syntax...
>>>
>>> con.close()

since Python uses double quotes to delimit string literals, so one solution is to use Python's triple quotes to delimit the string instead:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run('''SELECT 'hello' AS "My Column"''')
[['hello']]
>>>
>>> con.close()

another solution, that's especially useful if the identifier comes from an untrusted source, is to use the identifier() function, which correctly quotes and escapes the identifier as needed:

>>> from pg8000.native import Connection, identifier
>>>
>>> con = Connection("postgres", password="cpsnow")
>>>
>>> sql = f"SELECT 'hello' as {identifier('My Column')}"
>>> print(sql)
SELECT 'hello' as "My Column"
>>>
>>> con.run(sql)
[['hello']]
>>>
>>> con.close()

this approach guards against SQL injection attacks . One thing to note if you're using explicit schemas (eg. pg_catalog.pg_language) is that the schema name and table name are both separate identifiers. So to escape them you'd do:

>>> from pg8000.native import Connection, identifier
>>>
>>> con = Connection("postgres", password="cpsnow")
>>>
>>> query = (
...     f"SELECT lanname FROM {identifier('pg_catalog')}.{identifier('pg_language')} "
...     f"WHERE lanname = 'sql'"
... )
>>> print(query)
SELECT lanname FROM pg_catalog.pg_language WHERE lanname = 'sql'
>>>
>>> con.run(query)
[['sql']]
>>>
>>> con.close()

Custom adapter from a Python type to a PostgreSQL type

pg8000 has a mapping from Python types to PostgreSQL types for when it needs to send SQL parameters to the server. The default mapping that comes with pg8000 is designed to work well in most cases, but you might want to add or replace the default mapping.

A Python datetime.timedelta object is sent to the server as a PostgreSQL interval type, which has the oid 1186. But let's say we wanted to create our own Python class to be sent as an interval type. Then we'd have to register an adapter:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> class MyInterval(str):
...     pass
>>>
>>> def my_interval_out(my_interval):
...     return my_interval  # Must return a str
>>>
>>> con.register_out_adapter(MyInterval, my_interval_out)
>>> con.run("SELECT CAST(:interval as interval)", interval=MyInterval("2 hours"))
[[datetime.timedelta(seconds=7200)]]
>>>
>>> con.close()

Note that it still came back as a datetime.timedelta object because we only changed the mapping from Python to PostgreSQL. See below for an example of how to change the mapping from PostgreSQL to Python.

Custom adapter from a PostgreSQL type to a Python type

pg8000 has a mapping from PostgreSQL types to Python types for when it receives SQL results from the server. The default mapping that comes with pg8000 is designed to work well in most cases, but you might want to add or replace the default mapping.

If pg8000 receives PostgreSQL interval type, which has the oid 1186, it converts it into a Python datetime.timedelta object. But let's say we wanted to create our own Python class to be used instead of datetime.timedelta. Then we'd have to register an adapter:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> class MyInterval(str):
...     pass
>>>
>>> def my_interval_in(my_interval_str):  # The parameter is of type str
...     return MyInterval(my_interval)
>>>
>>> con.register_in_adapter(1186, my_interval_in)
>>> con.run("SELECT \'2 years'")
[['2 years']]
>>>
>>> con.close()

Note that registering the 'in' adapter only afects the mapping from the PostgreSQL type to the Python type. See above for an example of how to change the mapping from PostgreSQL to Python.

Could Not Determine Data Type Of Parameter

Sometimes you'll get the could not determine data type of parameter error message from the server:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT :v IS NULL", v=None)
Traceback (most recent call last):
pg8000.exceptions.DatabaseError: {'S': 'ERROR', 'V': 'ERROR', 'C': '42P18', 'M': 'could not determine data type of parameter $1', 'F': 'postgres.c', 'L': '...', 'R': '...'}
>>>
>>> con.close()

One way of solving it is to put a CAST in the SQL:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT cast(:v as TIMESTAMP) IS NULL", v=None)
[[True]]
>>>
>>> con.close()

Another way is to override the type that pg8000 sends along with each parameter:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> con.run("SELECT :v IS NULL", v=None, types={'v': pg8000.native.TIMESTAMP})
[[True]]
>>>
>>> con.close()

Prepared Statements

Prepared statements can be useful in improving performance when you have a statement that's executed repeatedly. Here's an example:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection("postgres", password="cpsnow")
>>>
>>> # Create the prepared statement
>>> ps = con.prepare("SELECT cast(:v as varchar)")
>>>
>>> # Execute the statement repeatedly
>>> ps.run(v="speedy")
[['speedy']]
>>> ps.run(v="rapid")
[['rapid']]
>>> ps.run(v="swift")
[['swift']]
>>>
>>> # Close the prepared statement, releasing resources on the server
>>> ps.close()
>>>
>>> con.close()

Use Environment Variables As Connection Defaults

You might want to use the current user as the database username for example:

>>> import pg8000.native
>>> import getpass
>>>
>>> # Connect to the database with current user name
>>> username = getpass.getuser()
>>> connection = pg8000.native.Connection(username, password="cpsnow")
>>>
>>> connection.run("SELECT 'pilau'")
[['pilau']]
>>>
>>> connection.close()

or perhaps you may want to use some of the same environment variables that libpg uses :

>>> import pg8000.native
>>> from os import environ
>>>
>>> username = environ.get('PGUSER', 'postgres')
>>> password = environ.get('PGPASSWORD', 'cpsnow')
>>> host = environ.get('PGHOST', 'localhost')
>>> port = environ.get('PGPORT', '5432')
>>> database = environ.get('PGDATABASE')
>>>
>>> connection = pg8000.native.Connection(
...     username, password=password, host=host, port=port, database=database)
>>>
>>> connection.run("SELECT 'Mr Cairo'")
[['Mr Cairo']]
>>>
>>> connection.close()

It might be asked, why doesn't pg8000 have this behaviour built in? The thinking follows the second aphorism of The Zen of Python :

Explicit is better than implicit.

So we've taken the approach of only being able to set connection parameters using the pg8000.native.Connection() constructor.

Connect To PostgreSQL Over SSL

By default the ssl_context connection parameter has the value None which means pg8000 will attempt to connect to the server using SSL, and then fall back to a plain socket if the server refuses SSL. If you want to require SSL (ie. to fail if it's not achieved) then you can set ssl_context=True:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection('postgres', password="cpsnow", ssl_context=True)
>>> con.run("SELECT 'The game is afoot!'")
[['The game is afoot!']]
>>> con.close()

If on the other hand you want to connect over SSL with custom settings, set the ssl_context parameter to an ssl.SSLContext object:

>>> import pg8000.native
>>> import ssl
>>>
>>> ssl_context = ssl.create_default_context()
>>> ssl_context.check_hostname = False
>>> ssl_context.verify_mode = ssl.CERT_NONE
>>> con = pg8000.native.Connection(
...     'postgres', password="cpsnow", ssl_context=ssl_context)
>>> con.run("SELECT 'Work is the curse of the drinking classes.'")
[['Work is the curse of the drinking classes.']]
>>> con.close()

It may be that your PostgreSQL server is behind an SSL proxy server in which case you can give pg8000 the SSL socket with the sock parameter, and then set ssl_context=False which means that no attempt will be made to create an SSL connection to the server.

Server-Side Cursors

You can use the SQL commands DECLARE , FETCH, MOVE and CLOSE to manipulate server-side cursors. For example:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection('postgres', password="cpsnow")
>>> con.run("START TRANSACTION")
>>> con.run("DECLARE c SCROLL CURSOR FOR SELECT * FROM generate_series(1, 100)")
>>> con.run("FETCH FORWARD 5 FROM c")
[[1], [2], [3], [4], [5]]
>>> con.run("MOVE FORWARD 50 FROM c")
>>> con.run("FETCH BACKWARD 10 FROM c")
[[54], [53], [52], [51], [50], [49], [48], [47], [46], [45]]
>>> con.run("CLOSE c")
>>> con.run("ROLLBACK")
>>>
>>> con.close()

BLOBs (Binary Large Objects)

There's a set of SQL functions for manipulating BLOBs. Here's an example:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection('postgres', password="cpsnow")
>>>
>>> # Create a BLOB and get its oid
>>> data = b'hello'
>>> res = con.run("SELECT lo_from_bytea(0, :data)", data=data)
>>> oid = res[0][0]
>>>
>>> # Create a table and store the oid of the BLOB
>>> con.run("CREATE TEMPORARY TABLE image (raster oid)")
>>>
>>> con.run("INSERT INTO image (raster) VALUES (:oid)", oid=oid)
>>> # Retrieve the data using the oid
>>> con.run("SELECT lo_get(:oid)", oid=oid)
[[b'hello']]
>>>
>>> # Add some data to the end of the BLOB
>>> more_data = b' all'
>>> offset = len(data)
>>> con.run(
...     "SELECT lo_put(:oid, :offset, :data)",
...     oid=oid, offset=offset, data=more_data)
[['']]
>>> con.run("SELECT lo_get(:oid)", oid=oid)
[[b'hello all']]
>>>
>>> # Download a part of the data
>>> con.run("SELECT lo_get(:oid, 6, 3)", oid=oid)
[[b'all']]
>>>
>>> con.close()

Replication Protocol

The PostgreSQL Replication Protocol is supported using the replication keyword when creating a connection:

>>> import pg8000.native
>>>
>>> con = pg8000.native.Connection(
...    'postgres', password="cpsnow", replication="database")
>>>
>>> con.run("IDENTIFY_SYSTEM")
[['...', 1, '.../...', 'postgres']]
>>>
>>> con.close()

DB-API 2 Interactive Examples

These examples stick to the DB-API 2.0 standard.

Basic Example

Import pg8000, connect to the database, create a table, add some rows and then query the table:

>>> import pg8000.dbapi
>>>
>>> conn = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cursor = conn.cursor()
>>> cursor.execute("CREATE TEMPORARY TABLE book (id SERIAL, title TEXT)")
>>> cursor.execute(
...     "INSERT INTO book (title) VALUES (%s), (%s) RETURNING id, title",
...     ("Ender's Game", "Speaker for the Dead"))
>>> results = cursor.fetchall()
>>> for row in results:
...     id, title = row
...     print("id = %s, title = %s" % (id, title))
id = 1, title = Ender's Game
id = 2, title = Speaker for the Dead
>>> conn.commit()
>>>
>>> conn.close()

Query Using Functions

Another query, using some PostgreSQL functions:

>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cursor = con.cursor()
>>>
>>> cursor.execute("SELECT TO_CHAR(TIMESTAMP '2021-10-10', 'YYYY BC')")
>>> cursor.fetchone()
['2021 AD']
>>>
>>> con.close()

Interval Type

A query that returns the PostgreSQL interval type:

>>> import datetime
>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cursor = con.cursor()
>>>
>>> cursor.execute("SELECT timestamp '2013-12-01 16:06' - %s",
... (datetime.date(1980, 4, 27),))
>>> cursor.fetchone()
[datetime.timedelta(days=12271, seconds=57960)]
>>>
>>> con.close()

Point Type

A round-trip with a PostgreSQL point type:

>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cursor = con.cursor()
>>>
>>> cursor.execute("SELECT cast(%s as point)", ((2.3,1),))
>>> cursor.fetchone()
[(2.3, 1.0)]
>>>
>>> con.close()

Numeric Parameter Style

pg8000 supports all the DB-API parameter styles. Here's an example of using the 'numeric' parameter style:

>>> import pg8000.dbapi
>>>
>>> pg8000.dbapi.paramstyle = "numeric"
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cursor = con.cursor()
>>>
>>> cursor.execute("SELECT array_prepend(:1, CAST(:2 AS int[]))", (500, [1, 2, 3, 4],))
>>> cursor.fetchone()
[[500, 1, 2, 3, 4]]
>>> pg8000.dbapi.paramstyle = "format"
>>>
>>> con.close()

Autocommit

Following the DB-API specification, autocommit is off by default. It can be turned on by using the autocommit property of the connection:

>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> con.autocommit = True
>>>
>>> cur = con.cursor()
>>> cur.execute("vacuum")
>>> conn.autocommit = False
>>> cur.close()
>>>
>>> con.close()

Client Encoding

When communicating with the server, pg8000 uses the character set that the server asks it to use (the client encoding). By default the client encoding is the database's character set (chosen when the database is created), but the client encoding can be changed in a number of ways (eg. setting CLIENT_ENCODING in postgresql.conf). Another way of changing the client encoding is by using an SQL command. For example:

>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cur = con.cursor()
>>> cur.execute("SET CLIENT_ENCODING TO 'UTF8'")
>>> cur.execute("SHOW CLIENT_ENCODING")
>>> cur.fetchone()
['UTF8']
>>> cur.close()
>>>
>>> con.close()

JSON

JSON is sent to the server serialized, and returned de-serialized. Here's an example:

>>> import json
>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cur = con.cursor()
>>> val = ['Apollo 11 Cave', True, 26.003]
>>> cur.execute("SELECT cast(%s as json)", (json.dumps(val),))
>>> cur.fetchone()
[['Apollo 11 Cave', True, 26.003]]
>>> cur.close()
>>>
>>> con.close()

JSON queries can be have parameters:

>>> import pg8000.dbapi
>>>
>>> with pg8000.dbapi.connect("postgres", password="cpsnow") as con:
...     cur = con.cursor()
...     cur.execute(""" SELECT CAST('{"a":1, "b":2}' AS jsonb) @> %s """, ({"b": 2},))
...     for row in cur.fetchall():
...         print(row)
[True]

Retrieve Column Names From Results

Use the columns names retrieved from a query:

>>> import pg8000
>>> conn = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> c = conn.cursor()
>>> c.execute("create temporary table quark (id serial, name text)")
>>> c.executemany("INSERT INTO quark (name) VALUES (%s)", (("Up",), ("Down",)))
>>> #
>>> # Now retrieve the results
>>> #
>>> c.execute("select * from quark")
>>> rows = c.fetchall()
>>> keys = [k[0] for k in c.description]
>>> results = [dict(zip(keys, row)) for row in rows]
>>> assert results == [{'id': 1, 'name': 'Up'}, {'id': 2, 'name': 'Down'}]
>>>
>>> conn.close()

COPY from and to a file

The SQL COPY statement can be used to copy from and to a file or file-like object:

>>> from io import StringIO
>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cur = con.cursor()
>>> #
>>> # COPY from a stream to a table
>>> #
>>> stream_in = StringIO('1\telectron\n2\tmuon\n3\ttau\n')
>>> cur = con.cursor()
>>> cur.execute("create temporary table lepton (id serial, name text)")
>>> cur.execute("COPY lepton FROM stdin", stream=stream_in)
>>> #
>>> # Now COPY from a table to a stream
>>> #
>>> stream_out = StringIO()
>>> cur.execute("copy lepton to stdout", stream=stream_out)
>>> stream_out.getvalue()
'1\telectron\n2\tmuon\n3\ttau\n'
>>>
>>> con.close()

Server-Side Cursors

You can use the SQL commands DECLARE , FETCH, MOVE and CLOSE to manipulate server-side cursors. For example:

>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cur = con.cursor()
>>> cur.execute("START TRANSACTION")
>>> cur.execute(
...    "DECLARE c SCROLL CURSOR FOR SELECT * FROM generate_series(1, 100)")
>>> cur.execute("FETCH FORWARD 5 FROM c")
>>> cur.fetchall()
([1], [2], [3], [4], [5])
>>> cur.execute("MOVE FORWARD 50 FROM c")
>>> cur.execute("FETCH BACKWARD 10 FROM c")
>>> cur.fetchall()
([54], [53], [52], [51], [50], [49], [48], [47], [46], [45])
>>> cur.execute("CLOSE c")
>>> cur.execute("ROLLBACK")
>>>
>>> con.close()

BLOBs (Binary Large Objects)

There's a set of SQL functions for manipulating BLOBs. Here's an example:

>>> import pg8000.dbapi
>>>
>>> con = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cur = con.cursor()
>>>
>>> # Create a BLOB and get its oid
>>> data = b'hello'
>>> cur = con.cursor()
>>> cur.execute("SELECT lo_from_bytea(0, %s)", [data])
>>> oid = cur.fetchone()[0]
>>>
>>> # Create a table and store the oid of the BLOB
>>> cur.execute("CREATE TEMPORARY TABLE image (raster oid)")
>>> cur.execute("INSERT INTO image (raster) VALUES (%s)", [oid])
>>>
>>> # Retrieve the data using the oid
>>> cur.execute("SELECT lo_get(%s)", [oid])
>>> cur.fetchall()
([b'hello'],)
>>>
>>> # Add some data to the end of the BLOB
>>> more_data = b' all'
>>> offset = len(data)
>>> cur.execute("SELECT lo_put(%s, %s, %s)", [oid, offset, more_data])
>>> cur.execute("SELECT lo_get(%s)", [oid])
>>> cur.fetchall()
([b'hello all'],)
>>>
>>> # Download a part of the data
>>> cur.execute("SELECT lo_get(%s, 6, 3)", [oid])
>>> cur.fetchall()
([b'all'],)
>>>
>>> con.close()

Parameter Limit

The protocol that PostgreSQL uses limits the number of parameters to 6,5535. The following will give an error:

>>> import pg8000.dbapi
>>>
>>> conn = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cursor = conn.cursor()
>>> SIZE = 100000
>>> cursor.execute(
...    f"SELECT 1 WHERE 1 IN ({','.join(['%s'] * SIZE)})",
...    [1] * SIZE,
... )
Traceback (most recent call last):
struct.error: 'H' format requires 0 <= number <= 65535

One way of working round this problem is to use the unnest function:

>>> import pg8000.dbapi
>>>
>>> conn = pg8000.dbapi.connect(user="postgres", password="cpsnow")
>>> cursor = conn.cursor()
>>> SIZE = 100000
>>> cursor.execute(
...    "SELECT 1 WHERE 1 IN (SELECT unnest(CAST(%s AS int[])))",
...    [[1] * SIZE],
... )
>>> conn.close()

Type Mapping

The following table shows the default mapping between Python types and PostgreSQL types, and vice versa.

If pg8000 doesn't recognize a type that it receives from PostgreSQL, it will return it as a str type. This is how pg8000 handles PostgreSQL enum and XML types. It's possible to change the default mapping using adapters (see the examples).

Python Type	PostgreSQL Type	Notes
bool	bool
int	int4
str	text
float	float8
decimal.Decimal	numeric
bytes	bytea
datetime.datetime (without tzinfo)	timestamp without timezone	+/-infinity PostgreSQL values are represented as Python str values. If a timestamp is too big for datetime.datetime then a str is used.
datetime.datetime (with tzinfo)	timestamp with timezone	+/-infinity PostgreSQL values are represented as Python str values. If a timestamptz is too big for datetime.datetime then a str is used.
datetime.date	date	+/-infinity PostgreSQL values are represented as Python str values. If a date is too big for a datetime.date then a str is used.
datetime.time	time without time zone
datetime.timedelta	interval	If an interval is too big for datetime.timedelta then a PGInterval is used.
None	NULL
uuid.UUID	uuid
ipaddress.IPv4Address	inet
ipaddress.IPv6Address	inet
ipaddress.IPv4Network	inet
ipaddress.IPv6Network	inet
int	xid
list of int	INT4[]
list of float	FLOAT8[]
list of bool	BOOL[]
list of str	TEXT[]
int	int2vector	Only from PostgreSQL to Python
JSON	json, jsonb	The Python JSON is provided as a Python serialized string. Results returned as de-serialized JSON.
pg8000.Range	range	PostgreSQL multirange types are
tuple	composite type	Only from Python to PostgreSQL

Theory Of Operation

A concept is tolerated inside the microkernel only if moving it outside the kernel, i.e., permitting competing implementations, would prevent the implementation of the system's required functionality.

-- Jochen Liedtke, Liedtke's minimality principle

pg8000 is designed to be used with one thread per connection.

pg8000 communicates with the database using the PostgreSQL Frontend/Backend Protocol (FEBE). If a query has no parameters, pg8000 uses the 'simple query protocol'. If a query does have parameters, pg8000 uses the 'extended query protocol' with unnamed prepared statements. The steps for a query with parameters are:

1. Query comes in.

2. Send a PARSE message to the server to create an unnamed prepared statement.

3. Send a BIND message to run against the unnamed prepared statement, resulting in an unnamed portal on the server.

4. Send an EXECUTE message to read all the results from the portal.

It's also possible to use named prepared statements. In which case the prepared statement persists on the server, and represented in pg8000 using a PreparedStatement object. This means that the PARSE step gets executed once up front, and then only the BIND and EXECUTE steps are repeated subsequently.

There are a lot of PostgreSQL data types, but few primitive data types in Python. By default, pg8000 doesn't send PostgreSQL data type information in the PARSE step, in which case PostgreSQL assumes the types implied by the SQL statement. In some cases PostgreSQL can't work out a parameter type and so an explicit cast can be used in the SQL.

In the FEBE protocol, each query parameter can be sent to the server either as binary or text according to the format code. In pg8000 the parameters are always sent as text.

Occasionally, the network connection between pg8000 and the server may go down. If pg8000 encounters a network problem it'll raise an InterfaceError with the message network error and with the original exception set as the cause .

Native API Docs

pg8000.native.Error

Generic exception that is the base exception of the other error exceptions.

pg8000.native.InterfaceError

For errors that originate within pg8000.

pg8000.native.DatabaseError

For errors that originate from the server.

pg8000.native.Connection(user, host='localhost', database=None, port=5432, password=None, source_address=None, unix_sock=None, ssl_context=None, timeout=None, tcp_keepalive=True, application_name=None, replication=None, sock=None)

Creates a connection to a PostgreSQL database.

• user - The username to connect to the PostgreSQL server with. If your server character encoding is not ascii or utf8, then you need to provide user as bytes, eg. 'my_name'.encode('EUC-JP').
• host - The hostname of the PostgreSQL server to connect with. Providing this parameter is necessary for TCP/IP connections. One of either host or unix_sock must be provided. The default is localhost.
• database - The name of the database instance to connect with. If None then the PostgreSQL server will assume the database name is the same as the username. If your server character encoding is not ascii or utf8, then you need to provide database as bytes, eg. 'my_db'.encode('EUC-JP').
• port - The TCP/IP port of the PostgreSQL server instance. This parameter defaults to 5432, the registered common port of PostgreSQL TCP/IP servers.
• password - The user password to connect to the server with. This parameter is optional; if omitted and the database server requests password-based authentication, the connection will fail to open. If this parameter is provided but not requested by the server, no error will occur. If your server character encoding is not ascii or utf8, then you need to provide password as bytes, eg. 'my_password'.encode('EUC-JP').
• source_address - The source IP address which initiates the connection to the PostgreSQL server. The default is None which means that the operating system will choose the source address.
• unix_sock - The path to the UNIX socket to access the database through, for example, '/tmp/.s.PGSQL.5432'. One of either host or unix_sock must be provided.
• ssl_context - This governs SSL encryption for TCP/IP sockets. It can have four values:
  • None, the default, meaning that an attempt will be made to connect over SSL, but if this is rejected by the server then pg8000 will fall back to using a plain socket.
  • True, means use SSL with an ssl.SSLContext with the minimum of checks.
  • False, means to not attempt to create an SSL socket.
  • An instance of ssl.SSLContext which will be used to create the SSL connection.
• timeout - This is the time in seconds before the connection to the server will time out. The default is None which means no timeout.
• tcp_keepalive - If True then use TCP keepalive. The default is True.
• application_name - Sets the application_name. If your server character encoding is not ascii or utf8, then you need to provide values as bytes, eg. 'my_application_name'.encode('EUC-JP'). The default is None which means that the server will set the application name.
• replication - Used to run in streaming replication mode. If your server character encoding is not ascii or utf8, then you need to provide values as bytes, eg. 'database'.encode('EUC-JP').
• sock - A socket-like object to use for the connection. For example, sock could be a plain socket.socket, or it could represent an SSH tunnel or perhaps an ssl.SSLSocket to an SSL proxy. If an ssl.SSLContext is provided, then it will be used to attempt to create an SSL socket from the provided socket.

pg8000.native.Connection.notifications

A deque of server-side notifications received by this database connection (via the LISTEN / NOTIFY PostgreSQL commands). Each list item is a three-element tuple containing the PostgreSQL backend PID that issued the notify, the channel and the payload.

pg8000.native.Connection.notices

A deque of server-side notices received by this database connection.

pg8000.native.Connection.parameter_statuses

A dict of server-side parameter statuses received by this database connection.

pg8000.native.Connection.run(sql, stream=None, types=None, **kwargs)

Executes an sql statement, and returns the results as a list. For example:

con.run("SELECT * FROM cities where population > :pop", pop=10000)

• sql - The SQL statement to execute. Parameter placeholders appear as a : followed by the parameter name.
• stream - For use with the PostgreSQL COPY command. The nature of the parameter depends on whether the SQL command is COPY FROM or COPY TO.
  • COPY FROM - The stream parameter must be a readable file-like object or an iterable. If it's an iterable then the items can be str or binary.
  • COPY TO - The stream parameter must be a writable file-like object.
• types - A dictionary of oids. A key corresponds to a parameter.
• kwargs - The parameters of the SQL statement.

pg8000.native.Connection.row_count

This read-only attribute contains the number of rows that the last run() method produced (for query statements like SELECT) or affected (for modification statements like UPDATE.

The value is -1 if:

• No run() method has been performed yet.
• There was no rowcount associated with the last run().

pg8000.native.Connection.columns

A list of column metadata. Each item in the list is a dictionary with the following keys:

• name
• table_oid
• column_attrnum
• type_oid
• type_size
• type_modifier
• format

pg8000.native.Connection.close()

Closes the database connection.

pg8000.native.Connection.register_out_adapter(typ, out_func)

Register a type adapter for types going out from pg8000 to the server.

• typ - The Python class that the adapter is for.
• out_func - A function that takes the Python object and returns its string representation in the format that the server requires.

pg8000.native.Connection.register_in_adapter(oid, in_func)

Register a type adapter for types coming in from the server to pg8000.

• oid - The PostgreSQL type identifier found in the pg_type system catalog.
• in_func - A function that takes the PostgreSQL string representation and returns a corresponding Python object.

pg8000.native.Connection.prepare(sql)

Returns a PreparedStatement object which represents a prepared statement on the server. It can subsequently be repeatedly executed.

• sql - The SQL statement to prepare. Parameter placeholders appear as a : followed by the parameter name.

pg8000.native.PreparedStatement

A prepared statement object is returned by the pg8000.native.Connection.prepare() method of a connection. It has the following methods:

pg8000.native.PreparedStatement.run(**kwargs)

Executes the prepared statement, and returns the results as a tuple.

• kwargs - The parameters of the prepared statement.

pg8000.native.PreparedStatement.close()

Closes the prepared statement, releasing the prepared statement held on the server.

pg8000.native.identifier(ident)

Correctly quotes and escapes a string to be used as an SQL identifier .

• ident - The str to be used as an SQL identifier.

pg8000.native.literal(value)

Correctly quotes and escapes a value to be used as an SQL literal .

• value - The value to be used as an SQL literal.

DB-API 2 Docs

Properties

pg8000.dbapi.apilevel

The DBAPI level supported, currently "2.0".

pg8000.dbapi.threadsafety

Integer constant stating the level of thread safety the DBAPI interface supports. For pg8000, the threadsafety value is 1, meaning that threads may share the module but not connections.

pg8000.dbapi.paramstyle

String property stating the type of parameter marker formatting expected by the interface. This value defaults to "format", in which parameters are marked in this format: "WHERE name=%s".

As an extension to the DBAPI specification, this value is not constant; it can be changed to any of the following values:

• qmark - Question mark style, eg. WHERE name=?
• numeric - Numeric positional style, eg. WHERE name=:1
• named - Named style, eg. WHERE name=:paramname
• format - printf format codes, eg. WHERE name=%s
• pyformat - Python format codes, eg. WHERE name=%(paramname)s

pg8000.dbapi.STRING

String type oid.

pg8000.dbapi.BINARY

pg8000.dbapi.NUMBER

Numeric type oid.

pg8000.dbapi.DATETIME

Timestamp type oid

pg8000.dbapi.ROWID

ROWID type oid

Functions

pg8000.dbapi.connect(user, host='localhost', database=None, port=5432, password=None, source_address=None, unix_sock=None, ssl_context=None, timeout=None, tcp_keepalive=True, applicationa_name=None, replication=None, sock=None)

Creates a connection to a PostgreSQL database.

• user - The username to connect to the PostgreSQL server with. If your server character encoding is not ascii or utf8, then you need to provide user as bytes, eg. 'my_name'.encode('EUC-JP').
• host - The hostname of the PostgreSQL server to connect with. Providing this parameter is necessary for TCP/IP connections. One of either host or unix_sock must be provided. The default is localhost.
• database - The name of the database instance to connect with. If None then the PostgreSQL server will assume the database name is the same as the username. If your server character encoding is not ascii or utf8, then you need to provide database as bytes, eg. 'my_db'.encode('EUC-JP').
• port - The TCP/IP port of the PostgreSQL server instance. This parameter defaults to 5432, the registered common port of PostgreSQL TCP/IP servers.
• password - The user password to connect to the server with. This parameter is optional; if omitted and the database server requests password-based authentication, the connection will fail to open. If this parameter is provided but not requested by the server, no error will occur. If your server character encoding is not ascii or utf8, then you need to provide password as bytes, eg. 'my_password'.encode('EUC-JP').
• source_address - The source IP address which initiates the connection to the PostgreSQL server. The default is None which means that the operating system will choose the source address.
• unix_sock - The path to the UNIX socket to access the database through, for example, '/tmp/.s.PGSQL.5432'. One of either host or unix_sock must be provided.
• ssl_context - This governs SSL encryption for TCP/IP sockets. It can have four values:
  • None, the default, meaning that an attempt will be made to connect over SSL, but if this is rejected by the server then pg8000 will fall back to using a plain socket.
  • True, means use SSL with an ssl.SSLContext with the minimum of checks.
  • False, means to not attempt to create an SSL socket.
  • An instance of ssl.SSLContext which will be used to create the SSL connection.
• timeout - This is the time in seconds before the connection to the server will time out. The default is None which means no timeout.
• tcp_keepalive - If True then use TCP keepalive. The default is True.
• application_name - Sets the application_name. If your server character encoding is not ascii or utf8, then you need to provide values as bytes, eg. 'my_application_name'.encode('EUC-JP'). The default is None which means that the server will set the application name.
• replication - Used to run in streaming replication mode. If your server character encoding is not ascii or utf8, then you need to provide values as bytes, eg. 'database'.encode('EUC-JP').
• sock - A socket-like object to use for the connection. For example, sock could be a plain socket.socket, or it could represent an SSH tunnel or perhaps an ssl.SSLSocket to an SSL proxy. If an ssl.SSLContext is provided, then it will be used to attempt to create an SSL socket from the provided socket.

pg8000.dbapi.Date(year, month, day)

Construct an object holding a date value.

This property is part of the DBAPI 2.0 specification <http://www.python.org/dev/peps/pep-0249/>_.

Returns: datetime.date

pg8000.dbapi.Time(hour, minute, second)

Construct an object holding a time value.

Returns: datetime.time

pg8000.dbapi.Timestamp(year, month, day, hour, minute, second)

Construct an object holding a timestamp value.

Returns: datetime.datetime

pg8000.dbapi.DateFromTicks(ticks)

Construct an object holding a date value from the given ticks value (number of seconds since the epoch).

Returns: datetime.datetime

pg8000.dbapi.TimeFromTicks(ticks)

Construct an object holding a time value from the given ticks value (number of seconds since the epoch).

Returns: datetime.time

pg8000.dbapi.TimestampFromTicks(ticks)

Construct an object holding a timestamp value from the given ticks value (number of seconds since the epoch).

Returns: datetime.datetime

pg8000.dbapi.Binary(value)

Construct an object holding binary data.

Returns: bytes

Generic Exceptions

Pg8000 uses the standard DBAPI 2.0 exception tree as "generic" exceptions. Generally, more specific exception types are raised; these specific exception types are derived from the generic exceptions.

pg8000.dbapi.Warning

Generic exception raised for important database warnings like data truncations. This exception is not currently used by pg8000.

pg8000.dbapi.Error

Generic exception that is the base exception of all other error exceptions.

pg8000.dbapi.InterfaceError

Generic exception raised for errors that are related to the database interface rather than the database itself. For example, if the interface attempts to use an SSL connection but the server refuses, an InterfaceError will be raised.

pg8000.dbapi.DatabaseError

Generic exception raised for errors that are related to the database. This exception is currently never raised by pg8000.

pg8000.dbapi.DataError

Generic exception raised for errors that are due to problems with the processed data. This exception is not currently raised by pg8000.

pg8000.dbapi.OperationalError

Generic exception raised for errors that are related to the database's operation and not necessarily under the control of the programmer. This exception is currently never raised by pg8000.

pg8000.dbapi.IntegrityError

Generic exception raised when the relational integrity of the database is affected. This exception is not currently raised by pg8000.

pg8000.dbapi.InternalError

Generic exception raised when the database encounters an internal error. This is currently only raised when unexpected state occurs in the pg8000 interface itself, and is typically the result of a interface bug.

pg8000.dbapi.ProgrammingError

Generic exception raised for programming errors. For example, this exception is raised if more parameter fields are in a query string than there are available parameters.

pg8000.dbapi.NotSupportedError

Generic exception raised in case a method or database API was used which is not supported by the database.

Classes

pg8000.dbapi.Connection

A connection object is returned by the pg8000.dbapi.connect() function. It represents a single physical connection to a PostgreSQL database.

pg8000.dbapi.Connection.autocommit

Following the DB-API specification, autocommit is off by default. It can be turned on by setting this boolean pg8000-specific autocommit property to True.

pg8000.dbapi.Connection.close()

Closes the database connection.

pg8000.dbapi.Connection.cursor()

Creates a pg8000.dbapi.Cursor object bound to this connection.

pg8000.dbapi.Connection.rollback()

Rolls back the current database transaction.

pg8000.dbapi.Connection.tpc_begin(xid)

Begins a TPC transaction with the given transaction ID xid. This method should be called outside of a transaction (i.e. nothing may have executed since the last commit() or rollback(). Furthermore, it is an error to call commit() or rollback() within the TPC transaction. A ProgrammingError is raised, if the application calls commit() or rollback() during an active TPC transaction.

pg8000.dbapi.Connection.tpc_commit(xid=None)

When called with no arguments, tpc_commit() commits a TPC transaction previously prepared with tpc_prepare(). If tpc_commit() is called prior to tpc_prepare(), a single phase commit is performed. A transaction manager may choose to do this if only a single resource is participating in the global transaction.

When called with a transaction ID xid, the database commits the given transaction. If an invalid transaction ID is provided, a ProgrammingError will be raised. This form should be called outside of a transaction, and is intended for use in recovery.

On return, the TPC transaction is ended.

pg8000.dbapi.Connection.tpc_prepare()

Performs the first phase of a transaction started with .tpc_begin(). A ProgrammingError is be raised if this method is called outside of a TPC transaction.

After calling tpc_prepare(), no statements can be executed until tpc_commit() or tpc_rollback() have been called.

pg8000.dbapi.Connection.tpc_recover()

Returns a list of pending transaction IDs suitable for use with tpc_commit(xid) or tpc_rollback(xid).

pg8000.dbapi.Connection.tpc_rollback(xid=None)

When called with no arguments, tpc_rollback() rolls back a TPC transaction. It may be called before or after tpc_prepare().

When called with a transaction ID xid, it rolls back the given transaction. If an invalid transaction ID is provided, a ProgrammingError is raised. This form should be called outside of a transaction, and is intended for use in recovery.

On return, the TPC transaction is ended.

pg8000.dbapi.Connection.xid(format_id, global_transaction_id, branch_qualifier)

Create a Transaction IDs (only global_transaction_id is used in pg) format_id and branch_qualifier are not used in postgres global_transaction_id may be any string identifier supported by postgres returns a tuple (format_id, global_transaction_id, branch_qualifier)

pg8000.dbapi.Cursor

A cursor object is returned by the pg8000.dbapi.Connection.cursor() method of a connection. It has the following attributes and methods:

pg8000.dbapi.Cursor.arraysize

This read/write attribute specifies the number of rows to fetch at a time with pg8000.dbapi.Cursor.fetchmany(). It defaults to 1.

pg8000.dbapi.Cursor.connection

This read-only attribute contains a reference to the connection object (an instance of pg8000.dbapi.Connection) on which the cursor was created.

pg8000.dbapi.Cursor.rowcount

This read-only attribute contains the number of rows that the last execute() or executemany() method produced (for query statements like SELECT) or affected (for modification statements like UPDATE.

The value is -1 if:

• No execute() or executemany() method has been performed yet on the cursor.
• There was no rowcount associated with the last execute().
• At least one of the statements executed as part of an executemany() had no row count associated with it.

pg8000.dbapi.Cursor.description

This read-only attribute is a sequence of 7-item sequences. Each value contains information describing one result column. The 7 items returned for each column are (name, type_code, display_size, internal_size, precision, scale, null_ok). Only the first two values are provided by the current implementation.

pg8000.dbapi.Cursor.close()

Closes the cursor.

pg8000.dbapi.Cursor.execute(operation, args=None, stream=None)

Executes a database operation. Parameters may be provided as a sequence, or as a mapping, depending upon the value of pg8000.dbapi.paramstyle. Returns the cursor, which may be iterated over.

• operation - The SQL statement to execute.
• args - If pg8000.dbapi.paramstyle is qmark, numeric, or format, this argument should be an array of parameters to bind into the statement. If pg8000.dbapi.paramstyle is named, the argument should be a dict mapping of parameters. If pg8000.dbapi.paramstyle is pyformat, the argument value may be either an array or a mapping.
• stream - This is a pg8000 extension for use with the PostgreSQL COPY command. For a COPY FROM the parameter must be a readable file-like object, and for COPY TO it must be writable.

pg8000.dbapi.Cursor.executemany(operation, param_sets)

Prepare a database operation, and then execute it against all parameter sequences or mappings provided.

• operation - The SQL statement to execute.
• parameter_sets - A sequence of parameters to execute the statement with. The values in the sequence should be sequences or mappings of parameters, the same as the args argument of the pg8000.dbapi.Cursor.execute() method.

pg8000.dbapi.Cursor.callproc(procname, parameters=None)

Call a stored database procedure with the given name and optional parameters.

• procname - The name of the procedure to call.
• parameters - A list of parameters.

pg8000.dbapi.Cursor.fetchall()

Fetches all remaining rows of a query result.

Returns: A sequence, each entry of which is a sequence of field values making up a row.

pg8000.dbapi.Cursor.fetchmany(size=None)

Fetches the next set of rows of a query result.

• size - The number of rows to fetch when called. If not provided, the pg8000.dbapi.Cursor.arraysize attribute value is used instead.

Returns: A sequence, each entry of which is a sequence of field values making up a row. If no more rows are available, an empty sequence will be returned.

pg8000.dbapi.Cursor.fetchone()

Fetch the next row of a query result set.

Returns: A row as a sequence of field values, or None if no more rows are available.

pg8000.dbapi.Cursor.setinputsizes(*sizes)

Used to set the parameter types of the next query. This is useful if it's difficult for pg8000 to work out the types from the parameters themselves (eg. for parameters of type None).

• sizes - Positional parameters that are either the Python type of the parameter to be sent, or the PostgreSQL oid. Common oids are available as constants such as pg8000.STRING, pg8000.INTEGER, pg8000.TIME etc.

pg8000.dbapi.Cursor.setoutputsize(size, column=None)

Not implemented by pg8000.

pg8000.dbapi.Interval

An Interval represents a measurement of time. In PostgreSQL, an interval is defined in the measure of months, days, and microseconds; as such, the pg8000 interval type represents the same information.

Note that values of the pg8000.dbapi.Interval.microseconds, pg8000.dbapi.Interval.days, and pg8000.dbapi.Interval.months properties are independently measured and cannot be converted to each other. A month may be 28, 29, 30, or 31 days, and a day may occasionally be lengthened slightly by a leap second.

Design Decisions

For the Range type, the constructor follows the PostgreSQL range constructor functions which makes [closed, open) the easiest to express:

>>> from pg8000.types import Range
>>>
>>> pg_range = Range(2, 6)

Tests

• Install tox: pip install tox

• Enable the PostgreSQL hstore extension by running the SQL command: create extension hstore;

• Add a line to pg_hba.conf for the various authentication options:

  host    pg8000_md5           all        127.0.0.1/32            md5
  host    pg8000_gss           all        127.0.0.1/32            gss
  host    pg8000_password      all        127.0.0.1/32            password
  host    pg8000_scram_sha_256 all        127.0.0.1/32            scram-sha-256
  host    all                  all        127.0.0.1/32            trust
  

• Set password encryption to scram-sha-256 in postgresql.conf: password_encryption = 'scram-sha-256'

• Set the password for the postgres user: ALTER USER postgresql WITH PASSWORD 'pw';

• Run tox from the pg8000 directory: tox

This will run the tests against the Python version of the virtual environment, on the machine, and the installed PostgreSQL version listening on port 5432, or the PGPORT environment variable if set.

Benchmarks are run as part of the test suite at tests/test_benchmarks.py.

Doing A Release Of pg8000

Run tox to make sure all tests pass, then update the release notes, then do:

git tag -a x.y.z -m "version x.y.z"
rm -r dist
python -m build
twine upload dist/*

Release Notes

Version 1.31.2, 2024-04-28

• Fix bug where parameter_statuses fails for non-ascii encoding.
• Add support for Python 3.12

Version 1.31.1, 2024-04-01

• Move to src style layout, and also for packaging use Hatch rather than setuptools. This means that if the source distribution has a directory added to it (as is needed for packaging for OS distributions) the package can still be built.

Version 1.31.0, 2024-03-31

• Now the ssl_context connection parameter can have one of four values:
  • None - The default, meaning it'll try and connect over SSL but fall back to a plain socket if not.
  • True - Will try and connect over SSL and fail if not.
  • False - It'll not try to connect over SSL.
  • SSLContext object - It'll use this object to connect over SSL.

Version 1.30.5, 2024-02-22

• Fix bug that now means the number of parameters cam be as high as an unsigned 16 bit integer will go.

Version 1.30.4, 2024-01-03

• Add support for more range and multirange types.
• Make the Connection.parameter_statuses property a dict rather than a dequeue.

Version 1.30.3, 2023-10-31

• Fix problem with PG date overflowing Python types. Now we return the str we got from the server if we can't parse it.

Version 1.30.2, 2023-09-17

• Bug fix where dollar-quoted string constants weren't supported.

Version 1.30.1, 2023-07-29

• There was a problem uploading the previous version (1.30.0) to PyPI because the markup of the README.rst was invalid. There's now a step in the automated tests to check for this.

Version 1.30.0, 2023-07-27

• Remove support for Python 3.7
• Add a sock keyword parameter for creating a connection from a pre-configured socket.

Version 1.29.8, 2023-06-16

• Ranges don't work with legacy API.

Version 1.29.7, 2023-06-16

• Add support for PostgreSQL range and multirange types. Previously pg8000 would just return them as strings, but now they're returned as Range and lists of Range.
• The PostgreSQL record type is now returned as a tuple of strings, whereas before it was returned as one string.

Version 1.29.6, 2023-05-29

• Fixed two bugs with composite types. Nulls should be represented by an empty string, and in an array of composite types, the elements should be surrounded by double quotes.

Version 1.29.5, 2023-05-09

• Fixed bug where pg8000 didn't handle the case when the number of bytes received from a socket was fewer than requested. This was being interpreted as a network error, but in fact we just needed to wait until more bytes were available.
• When using the PGInterval type, if a response from the server contained the period millennium, it wasn't recognised. This was caused by a spelling mistake where we had millenium rather than millennium.
• Added support for sending PostgreSQL composite types. If a value is sent as a tuple, pg8000 will send it to the server as a ( delimited composite string.

Version 1.29.4, 2022-12-14

• Fixed bug in pg8000.dbapi in the setinputsizes() method where if a size was a recognized Python type, the method failed.

Version 1.29.3, 2022-10-26

• Upgrade the SCRAM library to version 1.4.3. This adds support for the case where the client supports channel binding but the server doesn't.

Version 1.29.2, 2022-10-09

• Fixed a bug where in a literal array, items such as \n and \r weren't escaped properly before being sent to the server.
• Fixed a bug where if the PostgreSQL server has a half-hour time zone set, values of type timestamp with time zone failed. This has been fixed by using the parse function of the dateutil package if the datetime parser fails.

Version 1.29.1, 2022-05-23

• In trying to determine if there's been a failed commit, check for ROLLBACK TO SAVEPOINT.

Version 1.29.0, 2022-05-21

• Implement a workaround for the silent failed commit bug.
• Previously if an empty string was sent as the query an exception would be raised, but that isn't done now.

Version 1.28.3, 2022-05-18

• Put back __version__ attributes that were inadvertently removed.

Version 1.28.2, 2022-05-17

• Use a build system that's compliant with PEP517.

Version 1.28.1, 2022-05-17

• If when doing a COPY FROM the stream parameter is an iterator of str, pg8000 used to silently append a newline to the end. That no longer happens.

Version 1.28.0, 2022-05-17

• When using the COPY FROM SQL statement, allow the stream parameter to be an iterable.

Version 1.27.1, 2022-05-16

• The seconds attribute of PGInterval is now always a float, to cope with fractional seconds.
• Updated the interval parsers for iso_8601 and sql_standard to take account of fractional seconds.

Version 1.27.0, 2022-05-16

• It used to be that by default, if pg8000 received an interval type from the server and it was too big to fit into a datetime.timedelta then an exception would be raised. Now if an interval is too big for datetime.timedelta a PGInterval is returned.
• pg8000 now supports all the output formats for an interval (postgres, postgres_verbose, iso_8601 and sql_standard).

Version 1.26.1, 2022-04-23

• Make sure all tests are run by the GitHub Actions tests on commit.
• Remove support for Python 3.6
• Remove support for PostgreSQL 9.6

Version 1.26.0, 2022-04-18

• When connecting, raise an InterfaceError('network error') rather than let the underlying struct.error float up.
• Make licence text the same as that used by the OSI. Previously the licence wording differed slightly from the BSD 3 Clause licence at https://opensource.org/licenses/BSD-3-Clause. This meant that automated tools didn't pick it up as being Open Source. The changes are believed to not alter the meaning of the license at all.

Version 1.25.0, 2022-04-17

• Fix more cases where a ResourceWarning would be raise because of a socket that had been left open.
• We now have a single InterfaceError with the message 'network error' for all network errors, with the underlying exception held in the cause of the exception.

Version 1.24.2, 2022-04-15

• To prevent a ResourceWarning close socket if a connection can't be created.

Version 1.24.1, 2022-03-02

• Return pg +/-infinity dates as str. Previously +/-infinity pg values would cause an error when returned, but now we return +/-infinity as strings.

Version 1.24.0, 2022-02-06

• Add SQL escape functions identifier() and literal() to the native API. For use when a query can't be parameterised and the SQL string has to be created using untrusted values.

Version 1.23.0, 2021-11-13

• If a query has no parameters, then the query will no longer be parsed. Although there are performance benefits for doing this, the main reason is to avoid query rewriting, which can introduce errors.

Version 1.22.1, 2021-11-10

• Fix bug in PGInterval type where str() failed for a millennia value.

Version 1.22.0, 2021-10-13

• Rather than specifying the oids in the Parse step of the Postgres protocol, pg8000 now omits them, and so Postgres will use the oids it determines from the query. This makes the pg8000 code simpler and also it should also make the nuances of type matching more straightforward.