EBOOK – REDIS IN ACTION

This book covers the use of Redis, an in-memory database/data structure server.

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A.4 Hello Redis

After Redis itself is installed, you need to ensure that Python has the proper libraries
for accessing Redis. If you followed the earlier instructions, you may still have a command
prompt open. In this command prompt (you can open a new one if you closed
the old one), you’ll run Python. (Windows users can refer to how you ran Python during
the setup procedure.) Inside of the Python console, you’ll try connecting to Redis
and issue a couple commands, as shown in the next listing.

Listing A.7Testing Redis from Python
~:$ python

Start Python so that you can verify everything is up and running correctly.

Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.

*insert a tooltip/decription here*

>>> import redis

Import the redis library; it will automatically use the hiredis C accelerator library if it’s available.

>>> conn = redis.Redis()

Create a connection to Redis.

>>> conn.set('hello', 'world')
True

Set a value and see that it was set.

>>> conn.get('hello')
'world'

Get the value you just set.

RUNNING PYTHON IN OTHER WAYSThough you can run Python in a standard
terminal, there are a variety of other more “fully featured” ways to have a
Python console available. A basic editor and console called Idle ships with
Python on Windows and OS X; you can also install it on Linux (install the
idle-python2.6 or idle-python2.7 package, as relevant). In a console, you
can run python -m idlelib.idle from the command line, and Idle should
load. Idle is a fairly basic editor and Python console itself, so if you’re new to
programming, it should be a gentle introduction. Many other people have
found IPython to be the Python console of choice, offering a list of amazing features too long to mention here. Whether you go basic or fully featured,
you can’t go wrong.

REDIS ON OS X AND WINDOWSRight now, precompiled versions of Redis for
Windows and OS X are from the 2.4 series. In some chapters, we use features
that are only available in the Redis 2.6 and later series. If you find that something
we do doesn’t work, and you’re using Redis 2.4, it’s probably because
the feature or usage was added in Redis 2.6. See the notes in chapter 3 for
specific examples.

CONFIGURING REDISBy default, Redis should be configured to keep your data
using either snapshots or append-only files, and as long as you execute shutdown
on a client, Redis should keep your data around. Depending on how you
started it, Redis may be keeping the on-disk version of data in the same path
as the path you’re running it from. To update that, you’ll want to edit
redis.conf and use system startup scripts appropriate for your platform
(remember to move your data to the newly configured path). More information
about configuring Redis is available in chapter 4.

IS HIREDIS AVAILABLE ON NON-LINUX PLATFORMS?For those who are using Windows
or OS X and peeked at the Debian/Ubuntu install instructions, you’ll
have noticed that we installed a library called hiredis to be used with Python.
This library is an accelerator that passes protocol processing to a C library.
Though this library can be compiled for OS X and Windows, binaries for
them aren’t readily downloadable on the internet. Also, because I didn’t have
you install a compiler, if you’re interested in compiling and using hiredis on
your platform, you’re on your own.

Periodically in other chapters, we’ll use the Python console to show interactions with
Redis. In other cases, we’ll show function definitions and executable statements outside
of a console. In those cases where we’re not using the console, it’s assumed that
those functions are defined in a Python module. If you haven’t used Python before,
you should read Python’s tutorial on modules and running modules as programs in
the first part of http://docs.python.org/tutorial/modules.html, up to and including
the section “Executing modules as scripts.”

If you’re the kind of person who can read through language documentation and
tutorials and just “get it,” and you haven’t spent a lot of time with Python in the past, you
may want to consider going through the Python language tutorial at http://docs.python.org/tutorial/. If you’re only interested in the important stuff where you’ll
learn the most about Python’s syntax and semantics, read sections 3-7, and then 9.10
and 9.11 (which are about generators, which we use a couple of times).

By now you’ll have Redis and a Python interpreter running. If you got here via a
reference from chapter 1, go back to really start using Redis from Python.

If you’re having difficulty installing Redis or Python, please post your questions or
read others’ answers on the Redis in Action Manning forum: http://mng.bz/vB6c.