Fixing lilypond-book 2.11.43

Upgrading from LilyPond 2.11.41 to 2.11.43 this morning broke lilypond-book. The problem seems to be due to a python versioning problem. A special import statement makes an easy fix. Details follow.

lilypond-book is a python script with the shell directive #!/usr/bin/python as the first line. No problem unless /usr/bin/python points to a version of python older than 2.4. This is, on my system, in fact the case.

   $ /usr/bin/python -V
   Python 2.3.5

Why is this is a problem? Because the python set( ) constructor didn't become a language built-in until version 2.4 or so. Prior to that, you had to invoke set( ) with something like sets.Set( ) after importing the sets module somewhere.

On my box I have python 2.5 installed and set as to run as the default python in my path.

   $ which python
   /Library/Frameworks/Python.framework/Versions/Current/bin/python
  
   $ `which python` --version
   Python 2.5