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General PyGreSQL programming information
----------------------------------------
PyGreSQL consists of two parts: the "classic" PyGreSQL interface
provided by the :mod:`pg` module and the newer
DB-API 2.0 compliant interface provided by the :mod:`pgdb` module.
If you use only the standard features of the DB-API 2.0 interface,
it will be easier to switch from PostgreSQL to another database
for which a DB-API 2.0 compliant interface exists.
The "classic" interface may be easier to use for beginners, and it
provides some higher-level and PostgreSQL specific convenience methods.
.. seealso::
**DB-API 2.0** (Python Database API Specification v2.0)
is a specification for connecting to databases (not only PostGreSQL)
from Python that has been developed by the Python DB-SIG in 1999.
The authoritative programming information for the DB-API is :pep:`0249`.
Both Python modules utilize the same lower level C extension module that
serves as a wrapper for the C API to PostgreSQL that is available in form
of the so-called "libpq" library.
This means you must have the libpq library installed as a shared library
on your client computer, in a version that is supported by PyGreSQL.
Depending on the client platform, you may have to set environment variables
like `PATH` or `LD_LIBRARY_PATH` so that PyGreSQL can find the library.
.. warning::
Note that PyGreSQL is not thread-safe on the connection level. Therefore
we recommend using `DBUtils <http://www.webwareforpython.org/DBUtils>`_
for multi-threaded environments, which supports both PyGreSQL interfaces.
Another option is using PyGreSQL indirectly as a database driver for the
high-level `SQLAlchemy <http://www.sqlalchemy.org/>`_ SQL toolkit and ORM,
which supports PyGreSQL starting with SQLAlchemy 1.1 and which provides a
way to use PyGreSQL in a multi-threaded environment using the concept of
"thread local storage". Database URLs for PyGreSQL take this form::
postgresql+pygresql://username:password@host:port/database
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