I am looking for a pure-python SQL library that would give access to both MySQL and PostgreSQL.
The only requirement is to run on Python 2.5+ and be pure-python, so it can be included with the script and still run on most platforms (no-install).
In fact I am looking for a simple solution that would allow me to write SQL and export the results as CSV files.
Two part answer:
A) This is absolutely possible.
B) Depending on your exact concerns, a pure-python may or may not be a good approach to your problem.
Explained:
The SqlAlchemy library comes with two components : the more popular "ORM" , and the "Core" which it sits on top of. Either one will let you write your SQL commands in the SqlAlchemy format (which is just Python); SqlAlchemy will then compile the statements to Mysql or PostgreSQL and connect to the appropriate database.
SqlAlchemy is a great library, and I recommend it for just about everything. While you do have to write your statements in their format, it's easy to pick up -- and you can switch to virtually any underlying database library you want... at any time. It's the perfect platform to use in any database project , whether or not you need to support multiple backends.
SqlAlchemy talks to the database via the standard DBAPI drivers, and does support multiple options for pure python, notably the pymysql and pypostgresql drivers ( http://docs.sqlalchemy.org/en/latest/core/engines.html#supported-dbapis )
As for writing csv, the standard library has you covered.
import csv
So the caveat?
The following may or may not apply to your situation:
Most higher level db modules in the python universe are still recommending mysql-python and psycopg - both of which are not pure-python and compile/link/configure against the installed database. This largely seems to be from a mix of API / integration concerns and the speed of the various pure-python packages compared to c-extensions when run under CPython.
There are pure-python drivers like I recommended, but most reviewers state that they're largely experimental. The pymysql authors claim stability and production readiness, some developers who blog have challenged that. As for what "stabile" or "experimental" means, that varies with the projects. Some have a changing API, others are incomplete, some are buggy.
You'd need to ensure that you can find pure-python drivers for each system that support the exact operations you need. This could be simple, or this could be messy. Whether you use SqlAlchemy or something else, you'll still face this concern when selecting a DBAPI driver.
The PyPy project ( pure-python python interpreter ) has a wiki listing the compatibility of various packages : https://bitbucket.org/pypy/compatibility/wiki/Home I would defer to them for specific driver suggestions. If PyPy is your intended platform, SqlAlchemy runs perfectly on it as well.
Are you looking for an ORM, or a single library that would allow you to write SQL statements directly and convert where there are differences?
I'm not sure whether psycopg2 is pure-python or not, but it certainly has bindings and works on all platforms. You'd still have to install at least psycopg2 to communicate with the PostgreSQL database as Python (as far as I know) doesn't ship with it natively.
From there, any additional ORM library you want would also need to be installed, but most are pure-python on-top of whatever backend they use.
Storm, Django, SQLAlchemy all have abstracted layers on top of their database layer - based on your description, Django is probably too large a framework for your needs (was for mine) but is a popular one, SQLAlchemy is a tried and true system - tho a bit clunky particularly if you have to deal with inheritance (in my opinion). I have heard that Storm is good, tho I haven't tested too much with it so I can't fully say.
If you are looking to mix and match (some tables in MySQL and some tables in PostgreSQL) vs. a single database that could be either MySQL or PostgreSQL, I've been working on an ORM called ORB that focuses more on object-oriented design and allows for multiple databases and relationships between databases. Right now it only supports PostgreSQL and Mongo, just cause I haven't needed MySQL, but I'd be up for writing that backend. The code for that can be found at http://docs.projexsoftware.com/api/orb
Use SQL-Alchemy. It will work with most database types, and certainly does work with postgres and MySQL.
