> Is this pattern common enough to create a constant for it? I doubt it (but have no numbers to back it up).

Indeed, the answer is "not really" ; and here at the numbers to back it up:
```
sw@gaia-10:~/easyconfigs$ grep ^sources */*/*eb|grep %s|cut -d: -f2|sort|uniq -c|sort -r|head
     21 sources = ['%s-%s.tgz' % (name.lower(), version)]
     16 sources = ['%sV%s.TAR.gz' % (name, version)]
     15 sources = ['%s_%s.tar.gz' % (name.lower(), '_'.join(version.split('.')))]
     10 sources = ['%s-%s.zip' % (name.lower(), version)]
     10 sources = ['%s-%s.tar' % (name, version)]
     10 sources = ['%s-%s%s.tgz' % (name.lower(), '-'.join(version.split('.')), versionsuffix)]
     10 sources = ['%s%s-src.tar.gz' % (name.lower(), version)]
      9 sources = ['%s-%s.tgz' % (name, version)]
      6 sources = ['%s_%s.tar.gz' % (name, version)]
      6 sources = ['%s-src-%s.tar.gz' % (name, version)]
```

so. no joy.