pywikibot has had special support for SVN version 1.6 and earlier, by manually parsing the SVN undocumented entries file (version 11 or earlier).
getversion_svn in the first revision (82d7a63) of core's version.py parsed entries and returned a formatted tag using
tag = '[%s] %s' % (t[0], t[1])
79843a6 (https://gerrit.wikimedia.org/r/#/c/86375/ - Feb 2014) then used this tag value in a URL to github.com to obtain a hash, resulting in an error from github, and an exception in Python. tag was updated for SVN v1.7+, but not v1.6 and earlier.
(after creating a .svn/entries in the version 10 file format)
core$ python pwb.py shell
Welcome to the Pywikibot interactive shell!
>>> import pywikibot
>>> pywikibot.version.getversion_svn()
WARNING: Http response status 400
Traceback (most recent call last):
File "<console>", line 1, in <module>
File ".../pywikibot/version.py", line 184, in getversion_svn
hsh = github_svn_rev2hash(tag, rev)
File ".../pywikibot/version.py", line 166, in github_svn_rev2hash
dom = xml.dom.minidom.parse(StringIO(data))
File "/usr/lib64/python2.7/xml/dom/minidom.py", line 1921, in parse
return expatbuilder.parse(file)
File "/usr/lib64/python2.7/xml/dom/expatbuilder.py", line 928, in parse
result = builder.parseFile(file)
File "/usr/lib64/python2.7/xml/dom/expatbuilder.py", line 207, in parseFile
parser.Parse(buffer, 0)
ExpatError: undefined entity: line 13, column 20(the same bug appears in compat.)