Unable to install blockdiag

Question

I am trying to install a python UML tool called blockdiag via this command:

sudo easy_install blockdiag

I get the following error and am unable to figure out how to fix it. I have received this kind error for the first time and I would appreciate if you would be kind enough to let me also know how to troubleshoot such errors.

Reading http://effbot.org/zone/pil-changes-115.htm
Download error: [Errno -2] Name or service not known -- Some packages may not be found!
Reading http://effbot.org/zone/pil-changes-115.htm
Reading http://effbot.org/downloads/#Imaging
Best match: PIL 1.1.7
Downloading http://effbot.org/media/downloads/PIL-1.1.7.tar.gz
Processing PIL-1.1.7.tar.gz
Running PIL-1.1.7/setup.py -q bdist_egg --dist-dir /tmp/easy_install-tx4P54/PIL-1.1.7/egg-dist-tmp-F4vgBr
WARNING: '' not a valid package name; please use only.-separated package names in setup.py
_imaging.c:75:20: error: Python.h: No such file or directory
In file included from libImaging/Imaging.h:14,
                 from _imaging.c:77:

Link to full install log and error

Answer 1

Do you have package python-dev installed? That's where Python.h comes from.

These are the steps to find this information out for yourself:

Run apt-file search Python.h to find all packages that provide files that have Python.h in their name (You might have to install apt-file first). This lists a lot of packages, but most provide files like Symbol-Tables-In-Python.html. The only packages that provide a Python.h file are pythonX.X-dbg and pythonX.X-dev packages. Now, -dbg packages contain debug version of programs, while -dev contain development files such as C header files, and Python.h is such a file.

This narrows the list of packages down to python2.6-dev, python2.7-dev, and python3.2-dev. One way to check which of these version is the canonical one is to simple remove the version number from the package name, and check if this exists: apt-cache show python-dev:

Package: python-dev
Priority: optional
Section: python
Installed-Size: 32
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
Original-Maintainer: Matthias Klose <doko@debian.org>
Architecture: all
Source: python-defaults
Version: 2.7.2-7ubuntu2
Depends: python (= 2.7.2-7ubuntu2), python2.7-dev (>= 2.7.2-3~)
Filename: pool/main/p/python-defaults/python-dev_2.7.2-7ubuntu2_all.deb
Size: 1008
MD5sum: d8ef295ca23c3f46298daaa0ccb25403
SHA1: 057d3802fb2afb2a4f85906d65fcb2589568a377
SHA256: 1f5340056e70d6ff573e43f42365b1fd96cee7870ec6ed42c3be4eba6216a092
Description-en: header files and a static library for Python (default)
 Header files, a static library and development tools for building
 Python modules, extending the Python interpreter or embedding Python
 in applications.
 .
 This package is a dependency package, which depends on Debian's default
 Python version (currently v2.7).
Homepage: http://www.python.org/
Description-md5: 93a1917c3f17606b40377d0b737c6c92
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Origin: Ubuntu
Supported: 18m

The Depends: line shows that it will install python2.7-dev, so you can just install python-dev.

Since I already had the correct packages installed, I could use locate Python.h and then dpkg -S /usr/include/python2.7/Python.h to find the package that contains Python.h.