virtualenv on Windows

A little while ago I suggested to someone using Windows to implement
virtualenv "later". So I thought I'd document my experience here.

In summary, it probably works well if you have Visual Studio. The
process outlined below shows a clumsy workaround if you don't.

Hope it helps someone

Mike

- - - - - -

$pip install virtualenv # first step (requires pip obviously)

$mkdir c:\users\miked\env

$virtualenv --no-site-packages c:\users\miked\env\proj-x
New python executable in c:\users\miked\env\proj-x\Scripts\python.exe
Installing setuptools, pip...done.

Now copy your "myproject-x" into c:\users\miked\env\proj-x\myproject-x

At this point on Linux one would install virtualenv-wrapper but that is
unfortunately not available for Windows so a simple workaround is ...

1. mkdir \users\miked\bin # could be anything eg \users\miked\bat

2. Add C:\users\miked\bin to the path environment variable

3. Create a batch file called C:\users\miked\bin\proj-x.bat containing:

cd \users\miked\env\proj-x\myproject-x
..\Scripts\activate

4. Create another batch file
C:\users\miked\env\proj-x\myproject-x\exit.bat containing:

cd \users\miked\
\users\miked\env\proj-x\Scripts\deactivate

5. Test the workaround by opening a command prompt somewhere and
entering proj-x. You should see:

C:\Documents and Settings\Mike Dewhirst\Desktop>cd
\users\miked\env\proj-x\myproject-x

C:\users\miked\env\proj-x\myproject-x>..\Scripts\activate
(proj-x) C:\users\miked\env\proj-x\myproject-x>

6. Test the exit batch file by entering exit at that command prompt:

C:\users\miked\env\proj-x\myproject-x>..\Scripts\activate
(proj-x) C:\users\miked\env\proj-x\myproject-x>exit

(proj-x) C:\users\miked\env\proj-x\myproject-x>cd \users\miked\

(proj-x) C:\users\miked>\users\miked\env\proj-x\Scripts\deactivate
C:\users\miked>

This should let you get into and out of the virtualenv quite easily.

Now comes the difficult bit for Windows - installing stuff in the new
Python's site-packages. First, though, discover what you already have
installed in your main site-packages:

pip freeze > requirements.txt # lists existing site-packages

Here is mine, most of which I don't want in proj-x

Django==1.5.4
Jinja2==2.7.1
MarkupSafe==0.18
Pygments==1.6
South==0.7.6
Sphinx==1.1.3
coverage==3.7
django-discover-runner==1.0
docutils==0.9.1
filemov==1.1.1-2728-py2.7
pillow==2.3.0
pss==1.38
psycopg2==2.4.5
py2exe==0.6.9
pytz==2012h
pywin32==218
virtualenv==1.11.2

So I edit it down to the following, create a directory and save it as
C:\users\miked\env\proj-x\requirements\requirements.txt

Django==1.5.4
South==0.7.6
coverage==3.7
django-discover-runner==1.0
pillow==2.3.0
psycopg2==2.4.5
pytz==2013.9

pip install -r C:\users\miked\env\proj-x\requirements\requirements.txt

And this where (my) problems start. First pip will download the packages
successfully but I don't have Visual Studio installed so those packages
requiring compilation don't get installed. Here is a snippet of pip
output after the downloads:

Installing collected packages: Django, South, coverage,
django-discover-runner, pillow, psycopg2, pytz
Running setup.py install for Django

... and so on until errors start to appear. In my case the signal is:

error: Unable to find vcvarsall.bat

Afterwards, pip freeze shows:

(proj-x) C:\users\miked\env\proj-x>pip freeze
Django==1.5.4
South==0.7.6
coverage==3.7
django-discover-runner==1.0

... which indicates pillow, psycopg2 and pytz did not install.

But how come they were installed in the main site-packages? That's
because they were originally downloaded from
http://www.lfd.uci.edu/~gohlke/pythonlibs/ and installed manually.

However, even after downloading from that site they cannot be installed
manually into a virtualenv! Only pip can do that. The only workaround I
have found is to manually copy them from the main site-packages to the
new virtualenv site-packages. Clumsy.

My proj-x requirements.txt file now looks like this ...

Django==1.5.4
South==0.7.6
coverage==3.7
django-discover-runner==1.0
# pillow==2.3.0 http://www.lfd.uci.edu/~gohlke/pythonlibs/
# psycopg2==2.4.5 http://www.lfd.uci.edu/~gohlke/pythonlibs/
# pytz==2013.9 http://www.lfd.uci.edu/~gohlke/pythonlibs/

After the above clumsy workaround everything works well and pip freeze
displays ...

Django==1.5.4
South==0.7.6
coverage==3.7
django-discover-runner==1.0
pillow==2.3.0
psycopg2==2.4.5
pytz==2013.9



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