.. _installation:

Installation
============

In short, if you use a :ref:`supported system<supported-systems>`::

    pip install --upgrade pip           # upgrade pip to at least 20.3
    pip install "psycopg[binary]"       # remove [binary] for PyPy

and you should be :ref:`ready to start <module-usage>`. Read further for
alternative ways to install.


.. _supported-systems:

Supported systems
-----------------

The Psycopg version documented here has *official and tested* support for:

- Python: from version 3.7 to 3.12

  - Python 3.6 supported before Psycopg 3.1

- PyPy: from version 3.9 to 3.10

  - **Note:** Only the pure Python version is supported.

- PostgreSQL: from version 10 to 16
- OS: Linux, macOS, Windows

The tests to verify the supported systems run in `Github workflows`__:
anything that is not tested there is not officially supported. This includes:

.. __: https://github.com/psycopg/psycopg/actions

- Unofficial Python distributions such as Conda;
- Alternative PostgreSQL implementation;
- macOS hardware and releases not available on Github workflows.

If you use an unsupported system, things might work (because, for instance, the
database may use the same wire protocol as PostgreSQL) but we cannot guarantee
the correct working or a smooth ride.


.. _binary-install:

Binary installation
-------------------

The quickest way to start developing with Psycopg 3 is to install the binary
packages by running::

    pip install "psycopg[binary]"

This will install a self-contained package with all the libraries needed.
**You will need pip 20.3 at least**: please run ``pip install --upgrade pip``
to update it beforehand.

The above package should work in most situations. It **will not work** in
some cases though.

If your platform is not supported you should proceed to a :ref:`local
installation <local-installation>` or a :ref:`pure Python installation
<pure-python-installation>`.

.. seealso::

    Did Psycopg 3 install ok? Great! You can now move on to the :ref:`basic
    module usage <module-usage>` to learn how it works.

    Keep on reading if the above method didn't work and you need a different
    way to install Psycopg 3.

    For further information about the differences between the packages see
    :ref:`pq-impl`.

.. warning::

   The binary installation is not supported by PyPy.


.. _local-installation:

Local installation
------------------

A "Local installation" results in a performing and maintainable library. The
library will include the speed-up C module and will be linked to the system
libraries (``libpq``, ``libssl``...) so that system upgrade of libraries will
upgrade the libraries used by Psycopg 3 too. This is the preferred way to
install Psycopg for a production site.

In order to perform a local installation you need some prerequisites:

- a C compiler,
- Python development headers (e.g. the ``python3-dev`` package).
- PostgreSQL client development headers (e.g. the ``libpq-dev`` package).
- The :program:`pg_config` program available in the :envvar:`PATH`.

You **must be able** to troubleshoot an extension build, for instance you must
be able to read your compiler's error message. If you are not, please don't
try this and follow the `binary installation`_ instead.

If your build prerequisites are in place you can run::

    pip install "psycopg[c]"

.. warning::

   The local installation is not supported by PyPy.


.. _pure-python-installation:

Pure Python installation
------------------------

If you simply install::

    pip install psycopg

without ``[c]`` or ``[binary]`` extras you will obtain a pure Python
implementation. This is particularly handy to debug and hack, but it still
requires the system libpq to operate (which will be imported dynamically via
`ctypes`).

In order to use the pure Python installation you will need the ``libpq``
installed in the system: for instance on Debian system you will probably
need::

    sudo apt install libpq5

.. note::

    The ``libpq`` is the client library used by :program:`psql`, the
    PostgreSQL command line client, to connect to the database.  On most
    systems, installing :program:`psql` will install the ``libpq`` too as a
    dependency.

If you are not able to fulfill this requirement please follow the `binary
installation`_.


.. _pool-installation:

Installing the connection pool
------------------------------

The :ref:`Psycopg connection pools <connection-pools>` are distributed in a
separate package from the `!psycopg` package itself, in order to allow a
different release cycle.

In order to use the pool you must install the ``pool`` extra, using ``pip
install "psycopg[pool]"``, or install the `psycopg_pool` package separately,
which would allow to specify the release to install more precisely.


Handling dependencies
---------------------

If you need to specify your project dependencies (for instance in a
``requirements.txt`` file, ``setup.py``, ``pyproject.toml`` dependencies...)
you should probably specify one of the following:

- If your project is a library, add a dependency on ``psycopg``. This will
  make sure that your library will have the ``psycopg`` package with the right
  interface and leaves the possibility of choosing a specific implementation
  to the end user of your library.

- If your project is a final application (e.g. a service running on a server)
  you can require a specific implementation, for instance ``psycopg[c]``,
  after you have made sure that the prerequisites are met (e.g. the depending
  libraries and tools are installed in the host machine).

In both cases you can specify which version of Psycopg to use using
`requirement specifiers`__.

.. __: https://pip.pypa.io/en/stable/cli/pip_install/#requirement-specifiers

If you want to make sure that a specific implementation is used you can
specify the :envvar:`PSYCOPG_IMPL` environment variable: importing the library
will fail if the implementation specified is not available. See :ref:`pq-impl`.
