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environmentName\Scripts\deactivate.bat How does virtualenv work When one creates an environment, inside it three folders are created: • bin: when one has the environment active, and executes a command like python, pip or easy_install, one of the binaries in this folder is ran, instead of the system’s. • include: it’s simply a link to the files installed with Python. • lib: this is another important folder. Just like include it has a folder named python, but in contrast to include, this one isn’t a link to the files installed with Python. Instead, the folder has two important things: • A link to some Python files. In this case, the .py • A folder, site-packages, which is where packages are installed when one uses pip or easy_install Q & A session (Part 1) Before I commented that one of the problems we had was that we couldn’t install two versions of the same library. What I never did is comment how this problem is solved. The solution is easy. You create a virtual environment to use with django 0.97, and another for 1.2. You can create as many virtual environments as you wish, and they’re isolated from each other. For production servers, there are configurations that can be set up in apache for it to use some specific virtual environment. Q & A session (Part 2) I create a virtualenv, activate it, and do pip freeze, and lots of things that I never installed appear in the environment. The default behavior of virtualenv when one creates an environment is to also create it with the packages one has installed in the system. For it not to do this, when you create the environment, you can do: virtualenv --no-site-packages environmentName This makes it create a completely empty environment. Lastly, another option to note is —python, which makes the virtual environment use that version of python (it is necessary to have installed that version for this to work). For instance, in my machine I have both Python 2.7 and 3.1, being 2.7 the default one. Thus, when I create an environment, it will be created with Python 2.7. For it to use Python 3.1, I have to do the following: virtualenv --python=python3.1 environmentName Q & A session (Part 3) There are some packages that have code written in C. What happens with those Well, in those cases pip or easy_install will try to build the C code when the package is installed. In distros like Ubuntu, I recommend installing: • build-essential • python-dev Those two packages make it much easier to build. However, in Windows it is not so easy. Several packages that have C code are distributed as an .exe too. However, those installers do not allow us to select where to install them. Here http://www.developerzen.com/2010/09/23/the-complete-guide-to-setting-up-python-develo is a very good guide on how to make it build packages as it downloads it. Q & A session (Part 4) Do you recommend installing system packages or is it better to use easy_install There are various distros that come with various python packages that can be installed in the system. For example: apt-get python-numpy python-reportlab python-pil But the versions that can be installed with apt-get are old. Here we’ll see some comparative examples: Package name Ubuntu 10.10 version PyPi version rst2pdf 0.14.2 0.16 reportlab 2.4.3 2.5 django 1.2.3 1.2.3 Thus, it depends on what one wants to do. For instance, if one wants to make a program work with Ubuntu, then one can create a virtual environment and install the same
versions that apt-get has, or directly install system-supplied ones. What I would NOT recommend is overwriting the installed version. For instance, if one does: apt-get python-reportlab Then you do NOT do: easy_install -U reportlab Not without using a virtual environment, because it could break the system.
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Issue 2: June 2011 In This Issue Is
Page 4 and 5: Pools 41 Free lists 42 Arenas 42 Fr
Page 6 and 7: How PyConAr2010 was made Author: Ho
Page 8 and 9: • A free entry event does not pro
Page 10 and 11: • What kind of bill(s) you can ac
Page 12 and 13: Lightning Talks at PyConAr 2010 Aut
Page 14 and 15: More event pictures Pictures in thi
Page 16 and 17: Through a new member’s eyes It is
Page 18 and 19: Pictures are courtesy of: http://ww
Page 20 and 21: id(greeting) 3068236156L >>> greeti
Page 22 and 23: @typer(int) def age(): return 25.5
Page 24 and 25: @route('/') def index(): return 'He
Page 26 and 27: In Django we will have Projects and
Page 28 and 29: The tools we’ve seen so far are m
Page 30 and 31: PyAfipWs: facilitating, extending a
Page 32 and 33: For those who don’t know Python a
Page 34 and 35: InfoPython - Measuring the Value of
Page 36 and 37: • Theories: This layer has module
Page 38 and 39: # Iterate over each ASNode and prin
Page 40 and 41: import gtk >>> w = gtk.Window() >>>
Page 42 and 43: Structure of an object pool In a po
Page 44 and 45: Partition of a set of 23778 objects
Page 46 and 47: • String lists → comma-separate
Page 48 and 49: Who is behind NINJA-IDE NINJA-IDE w
Page 50 and 51: • Code finder • Virtualenv supp
Page 52 and 53: • Though python knows how to read
Page 56 and 57: PET Challenge Authors: Juanjo Conti
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