# General PyGreSQL programming information

PyGreSQL consists of two parts: the “classic” PyGreSQL interface provided by the `pg` module and the newer DB-API 2.0 compliant interface provided by the `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.

See also

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 for multi-threaded environments, which supports both PyGreSQL interfaces.

Another option is using PyGreSQL indirectly as a database driver for the high-level SQLAlchemy 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