.. _installation:

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

Flask is a microframework and yet it depends on external libraries.  There
are various ways how you can install that library and this explains each
way and why there are multiple ways.

Flask depends on two external libraries: `Werkzeug
<http://werkzeug.pocoo.org/>`_ and `Jinja2 <http://jinja.pocoo.org/2/>`_.
The first one is responsible for interfacing WSGI the latter for rendering
templates.  Now you are maybe asking, what is WSGI?  WSGI is a standard
in Python that is basically responsible for ensuring that your application
is behaving in a specific way so that you can run it on different
environments (for example on a local development server, on an Apache2, on
lighttpd, on Google's App Engine or whatever you have in mind).

So how do you get all that on your computer in no time?  The most kick-ass
method is virtualenv, so let's look at that first.

virtualenv
----------

Virtualenv is what you want to use during development and in production if
you have shell access.  So first: what does virtualenv do?  If you are
like me and you like Python, chances are you want to use it for another
project as well.  Now the more projects you have, the more likely it is
that you will be working with different versions of Python itself or at
least an individual library.  Because let's face it: quite often libraries 
break backwards compatibility and it's unlikely that your application will
not have any dependencies, that just won't happen.  So virtualenv to the
rescue!

It basically makes it possible to have multiple side-by-side
"installations" of Python, each for your own project.  It's not actually
an installation but a clever way to keep things separated.

So let's see how that works!

If you are on OS X or Linux chances are that one of the following two
commands will for for you::

    $ sudo easy_install virtualenv

or even better::

    $ sudo pip install virtualenv

Chances are you have virtualenv installed on your system then.  Maybe it's
even in your package manager (on ubuntu try ``sudo apt-get install
python-virtualenv``).

If you are on Windows and missing the `easy_install` command you have to
install it first.  Check the :ref:`windows-easy-install` section for more
information about how to do that.  Once you have it installed, run the
same commands as above, but without the `sudo` part.

So now that you have virtualenv running just fire up a shell and create
your own environment.  I usually create a folder and a `env` folder
within::

    $ mkdir myproject
    $ cd myproject
    $ virtualenv env
    New python executable in env/bin/python
    Installing setuptools............done.

Now you only have to activate it, whenever you work with it.  On OS X and
Linux do the following::

    $ . env/bin/activate

(Note the whitespace between the dot and the script name.  This means
execute this file in context of the shell.  If the dot does not work for
whatever reason in your shell, try substituting it with ``source``)

If you are a Windows user, the following command is for you::

    $ env\scripts\activate

Either way, you should now be using your virtualenv (see how the prompt of
your shell has changed to show the virtualenv).

Now you can just enter the following command to get Flask activated in
your virtualenv::

    $ easy_install Flask

A few seconds later you are good to go.


System Wide Installation
------------------------

This is possible as well, but I would not recommend it.  Just run
`easy_install` with root rights::

    sudo easy_install Flask

(Run it in an Admin shell on Windows systems and without the `sudo`).


Living on the Edge
------------------

You want to work with the latest version of Flask, there are two ways: you
can either let `easy_install` pull in the development version or tell it
to operate on a git checkout.  Either way it's recommended to do that in a
virtualenv.

Get the git checkout in a new virtualenv and run in develop mode::

    $ git clone http://github.com/mitsuhiko/flask.git
    Initialized empty Git repository in ~/dev/flask/.git/
    $ cd flask
    $ virtualenv env
    $ . env/bin/activate
    New python executable in env/bin/python
    Installing setuptools............done.
    $ python setup.py develop
    ...
    Finished processing dependencies for Flask

This will pull in the dependencies and activate the git head as current
version.  Then you just have to ``git pull origin`` to get the latest
version.

To just get the development version without git, do this instead::

    $ mkdir flask
    $ cd flask
    $ virtualenv env
    $ . env/bin/activate
    New python executable in env/bin/python
    Installing setuptools............done.
    $ easy_install Flask==dev
    ...
    Finished processing dependencies for Flask==dev

.. _windows-easy-install:

`easy_install` on Windows
-------------------------

On Windows installation of `easy_install` is a little bit tricker because
on Windows slightly different rules apply, but it's not a biggy.  The
easiest way to accomplish that is downloading the `ez_setup.py`_ file and
running it.  (Double clicking should do the trick)

Once you have done that it's important to add the `easy_install` command
and other Python scripts to the path.  To do that you have to add the
Python installation's Script folder to the `PATH` variable.

To do that, right-click on your "Computer" desktop icon and click
"Properties".  On Windows Vista and Windows 7 then click on "Advanced System
settings", on Windows XP click on the "Advanced" tab instead.  Then click
on the "Environment variables" button and double click on the "Path"
variable in the "System variables" section.

There append the path of your Python interpreter's Script folder to the
end of the last (make sure you delimit it from existing values with a
semicolon).  Assuming you are using Python 2.6 on the default path, add
the following value::

    ;C:\Python26\Scripts

Then you are done.  To check that it worked, open the cmd and execute
"easy_install".  If you have UAC enabled it should prompt you for admin
privileges.


.. _ez_setup.py: http://peak.telecommunity.com/dist/ez_setup.py