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Edited the installation guide.
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mwcampbell authored and mitsuhiko committed Jun 26, 2010
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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
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).
Werkzeug is a toolkit for WSGI, the standard Python interface between web
applications and a variety of servers for both development and deployment.
Jinja2 renders templates.

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.
So how do you get all that on your computer quickly? There are many ways
which this section will explain, but the most kick-ass method is
virtualenv, so let's look at that first.

.. _virtualenv:

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!
Virtualenv is probably what you want to use during development, and in
production too if you have shell access there.

What problem does virtualenv solve? If you like Python as I do,
chances are you want to use it for other projects besides Flask-based
web applications. But the more projects you have, the more likely it is
that you will be working with different versions of Python itself, or at
least different versions of Python libraries. Let's face it; quite often
libraries break backwards compatibility, and it's unlikely that any serious
application will have zero dependencies. So what do you do if two or more
of your projects have conflicting dependencies?

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.
Virtualenv to the rescue! It basically enables multiple side-by-side
installations of Python, one for each project. It doesn't actually
install separate copies of Python, but it does provide a clever way
to keep different project environments isolated.

So let's see how that works!
So let's see how virtualenv works!

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

$ sudo easy_install virtualenv
Expand All @@ -49,33 +46,34 @@ 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``).
One of these will probably install virtualenv on your system. Maybe it's
even in your package manager. If you use Ubuntu, try::

$ sudo apt-get install python-virtualenv

If you are on Windows and missing the `easy_install` command you have to
If you are on Windows and don't have the `easy_install` command, you must
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.
same commands as above, but without the `sudo` prefix.

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::
Once you have virtualenv installed, just fire up a shell and create
your own environment. I usually create a project folder and an `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::
Now, whenever you want to work on a project, you only have to activate
the corresponding environment. 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``)
(Note the space between the dot and the script name. The dot means that
this script should run in the context of the current shell. If this command
does not work in your shell, try replacing the dot with ``source``)

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

Expand All @@ -95,23 +93,22 @@ 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
This is possible as well, but I do not recommend it. Just run
`easy_install` with root rights::

sudo easy_install Flask
$ sudo easy_install Flask

(Run it in an Admin shell on Windows systems and without the `sudo`).
(Run it in an Admin shell on Windows systems and without `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.
If 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, virtualenv is recommended.

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

$ git clone http://github.com/mitsuhiko/flask.git
Initialized empty Git repository in ~/dev/flask/.git/
Expand All @@ -124,9 +121,9 @@ Get the git checkout in a new virtualenv and run in develop mode::
...
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.
This will pull in the dependencies and activate the git head as the current
version inside the virtualenv. Then you just have to ``git pull origin``
to get the latest version.

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

Expand All @@ -145,31 +142,29 @@ To just get the development version without git, do this instead::
`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 Windows, installation of `easy_install` is a little bit tricker because
slightly different rules apply on Windows than on Unix-like systems, but
it's not difficult. The easiest way to do it is to download the
`ez_setup.py`_ file and run it. The easiest way to run the file is to
open your downloads folder and double-click on the file.

Next, add the `easy_install` command and other Python scripts to the
command search path, by adding your Python installation's Scripts folder
to the `PATH` environment variable. To do that, right-click on the
"Computer" icon on the Desktop or in the Start menu, and choose
"Properties". Then, on Windows Vista and Windows 7 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::
variable in the "System variables" section. There append the path of your
Python interpreter's Scripts folder; 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.
Then you are done. To check that it worked, open the Command Prompt and
execute ``easy_install``. If you have User Account Control enabled on
Windows Vista or Windows 7, it should prompt you for admin privileges.


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

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