Psycopg 2.9.3 documentation

Installation

Psycopg is a PostgreSQL adapter for the Python programming language. It is a wrapper for the libpq, the official PostgreSQL client library.

Quick Install

For most operating systems, the quickest way to install Psycopg is using the wheel package available on PyPI:

$ pip install psycopg2-binary

This will install a pre-compiled binary version of the module which does not require the build or runtime prerequisites described below. Make sure to use an up-to-date version of pip (you can upgrade it using something like pip install -U pip).

You may then import the psycopg2 package, as usual:

import psycopg2

# Connect to your postgres DB
conn = psycopg2.connect("dbname=test user=postgres")

# Open a cursor to perform database operations
cur = conn.cursor()

# Execute a query
cur.execute("SELECT * FROM my_data")

# Retrieve query results
records = cur.fetchall()

psycopg vs psycopg-binary

The psycopg2-binary package is meant for beginners to start playing with Python and PostgreSQL without the need to meet the build requirements.

If you are the maintainer of a published package depending on psycopg2 you shouldn’t use psycopg2-binary as a module dependency. For production use you are advised to use the source distribution.

The binary packages come with their own versions of a few C libraries, among which libpq and libssl, which will be used regardless of other libraries available on the client: upgrading the system libraries will not upgrade the libraries used by psycopg2. Please build psycopg2 from source if you want to maintain binary upgradeability.

Warning

The psycopg2 wheel package comes packaged, among the others, with its own libssl binary. This may create conflicts with other extension modules binding with libssl as well, for instance with the Python ssl module: in some cases, under concurrency, the interaction between the two libraries may result in a segfault. In case of doubts you are advised to use a package built from source.

Change in binary packages between Psycopg 2.7 and 2.8

In version 2.7.x, pip install psycopg2 would have tried to install automatically the binary package of Psycopg. Because of concurrency problems binary packages have displayed, psycopg2-binary has become a separate package, and from 2.8 it has become the only way to install the binary package.

If you are using Psycopg 2.7 and you want to disable the use of wheel binary packages, relying on the system libraries available on your client, you can use the pip --no-binary option, e.g.:

$ pip install --no-binary :all: psycopg2

which can be specified in your requirements.txt files too, e.g. use:

psycopg2>=2.7,<2.8 --no-binary psycopg2

to use the last bugfix release of the psycopg2 2.7 package, specifying to always compile it from source. Of course in this case you will have to meet the build prerequisites.

Prerequisites

The current psycopg2 implementation supports:

Python versions from 3.6 to 3.10
PostgreSQL server versions from 7.4 to 14
PostgreSQL client library version from 9.1

Build prerequisites

The build prerequisites are to be met in order to install Psycopg from source code, from a source distribution package, GitHub or from PyPI.

Psycopg is a C wrapper around the libpq PostgreSQL client library. To install it from sources you will need:

A C compiler.
The Python header files. They are usually installed in a package such as python-dev or python3-dev. A message such as error: Python.h: No such file or directory is an indication that the Python headers are missing.
The libpq header files. They are usually installed in a package such as libpq-dev. If you get an error: libpq-fe.h: No such file or directory you are missing them.
The pg_config program: it is usually installed by the libpq-dev package but sometimes it is not in a PATH directory. Having it in the PATH greatly streamlines the installation, so try running pg_config --version: if it returns an error or an unexpected version number then locate the directory containing the pg_config shipped with the right libpq version (usually /usr/lib/postgresql/X.Y/bin/) and add it to the PATH:
$ export PATH=/usr/lib/postgresql/X.Y/bin/:$PATH
You only need pg_config to compile psycopg2, not for its regular usage.

Once everything is in place it’s just a matter of running the standard:

$ pip install psycopg2

or, from the directory containing the source code:

$ python setup.py build
$ python setup.py install

Runtime requirements

Unless you compile psycopg2 as a static library, or you install it from a self-contained wheel package, it will need the libpq library at runtime (usually distributed in a libpq.so or libpq.dll file). psycopg2 relies on the host OS to find the library if the library is installed in a standard location there is usually no problem; if the library is in a non-standard location you will have to tell Psycopg how to find it, which is OS-dependent (for instance setting a suitable LD_LIBRARY_PATH on Linux).

Note

The libpq header files used to compile psycopg2 should match the version of the library linked at runtime. If you get errors about missing or mismatching libraries when importing psycopg2 check (e.g. using ldd) if the module psycopg2/_psycopg.so is linked to the right libpq.so.

Note

Whatever version of libpq psycopg2 is compiled with, it will be possible to connect to PostgreSQL servers of any supported version: just install the most recent libpq version or the most practical, without trying to match it to the version of the PostgreSQL server you will have to connect to.

Non-standard builds

If you have less standard requirements such as:

creating a debug build,
using pg_config not in the PATH,

then take a look at the setup.cfg file.

Some of the options available in setup.cfg are also available as command line arguments of the build_ext sub-command. For instance you can specify an alternate pg_config location using:

$ python setup.py build_ext --pg-config /path/to/pg_config build

Use python setup.py build_ext --help to get a list of the options supported.

Creating a debug build

In case of problems, Psycopg can be configured to emit detailed debug messages, which can be very useful for diagnostics and to report a bug. In order to create a debug package:

Download and unpack the Psycopg source package (the .tar.gz package).
Edit the setup.cfg file adding the PSYCOPG_DEBUG flag to the define option.
Compile and install the package.
Set the PSYCOPG_DEBUG environment variable:

$ export PSYCOPG_DEBUG=1

Run your program (making sure that the psycopg2 package imported is the one you just compiled and not e.g. the system one): you will have a copious stream of informations printed on stderr.

Non-standard Python Implementation

The psycopg2 package is the current mature implementation of the adapter: it is a C extension and as such it is only compatible with CPython. If you want to use Psycopg on a different Python implementation (PyPy, Jython, IronPython) there is a couple of alternative:

a Ctypes port, but it is not as mature as the C implementation yet and it is not as feature-complete;
a CFFI port which is currently more used and reported more efficient on PyPy, but please be careful of its version numbers because they are not aligned to the official psycopg2 ones and some features may differ.

Running the test suite

Once psycopg2 is installed you can run the test suite to verify it is working correctly. From the source directory, you can run:

$ python -c "import tests; tests.unittest.main(defaultTest='tests.test_suite')" --verbose

The tests run against a database called psycopg2_test on UNIX socket and the standard port. You can configure a different database to run the test by setting the environment variables:

PSYCOPG2_TESTDB
PSYCOPG2_TESTDB_HOST
PSYCOPG2_TESTDB_PORT
PSYCOPG2_TESTDB_USER

The database should already exist before running the tests.

If you still have problems

Try the following. In order:

Read again the Build prerequisites.
Read the FAQ.
Google for psycopg2 your error message. Especially useful the week after the release of a new OS X version.
Write to the Mailing List.
If you think that you have discovered a bug, test failure or missing feature please raise a ticket in the bug tracker.
Complain on your blog or on Twitter that psycopg2 is the worst package ever and about the quality time you have wasted figuring out the correct ARCHFLAGS. Especially useful from the Starbucks near you.

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Psycopg 2.9.3 documentation- python连接pgSQL