[MacPorts] #25040: lilypond 2.12.3 FTB with Python 3 selected

[MacPorts]

#25040: lilypond 2.12.3 FTB with Python 3 selected
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 Reporter:  gale@…          |       Owner:  macports-tickets@…                   
     Type:  defect          |      Status:  new                                  
 Priority:  Normal          |   Milestone:                                       
Component:  ports           |     Version:  1.8.2                                
 Keywords:                  |        Port:  lilypond                             
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 The first point is that this port does not have an
 explicit dependency on any version of python.
 In fact, it works for any 2.4 <= python < 3.
 (I tested python27, and from the comments in the
 python code it appears to support at least back to 2.4.)
 But the port pulls in specifically python25 indirectly via
 at least one of its deps, mftrace. So python25 should be
 added as an explicit dep of lilypond to show that not
 only do we need python25 installed, we need it selected.

 Now to the basic issue of not building when Python 3
 is selected.

 As has been pointed out before, this is going to be an
 increasingly common problem, as more and more
 MacPorts users make the switch to Python 3 while not
 all upstream sources support it yet for the snippets
 of Python so many ports contain.

 Here is a general solution for when a port depends on a specific
 version of Python, not just the case of 3 vs. 2: port
 creates its own symlink to the required python version inside
 a directory it controls, then pushes that directory onto the
 front of PATH for the duration of the build. (Perhaps for
 configure also.)

 Alternatively, for any particular port, we can try to
 create a patch that makes the port's python code
 compatible with Python 3. Usually, it's just a matter of
 de-tabifying sloppy indentation, and changing
 "print >> f" to "f.write". (Thankfully, the Python core
 devs have not yet removed support in Python 3 for the
 old "%" string formatting operator, as threatened.)

 But in some cases the conversion could turn out to
 involve real work, so it should really be a job for
 upstream. In practice we can't wait for that to
 happen; it could take months or years.

 So I recommend the PATH hack.

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Ticket URL: <http://trac.macports.org/ticket/25040>
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