gifti to_xml TypeError: cannot serialize 0 (type int)

[yarikoptic]

happens with 2.0.1-634-g82a261c
After the fixup #468 ran into another failure which I am not sure at which stage should be addressed, so decided just to report with details:

======================================================================
ERROR: test_surf_gifti (mvpa2.tests.test_surfing.SurfTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/yoh/proj/pymvpa/pymvpa/mvpa2/testing/tools.py", line 278, in newfunc
    func(*(arg + (filename,)), **kw)
  File "/home/yoh/proj/pymvpa/pymvpa/mvpa2/tests/test_surfing.py", line 1104, in test_surf_gifti
    surf.write(fn, s)
  File "/home/yoh/proj/pymvpa/pymvpa/mvpa2/support/nibabel/surf.py", line 2229, in write
    surf_gifti.write(fn, s, overwrite=overwrite)
  File "/home/yoh/proj/pymvpa/pymvpa/mvpa2/support/nibabel/surf_gifti.py", line 256, in write
    xml = to_xml(s, fn)
  File "/home/yoh/proj/pymvpa/pymvpa/mvpa2/support/nibabel/surf_gifti.py", line 219, in to_xml
    xml = img.to_xml().encode('utf-8')
  File "/home/yoh/proj/nipy/nipy-suite/nibabel/nibabel/gifti/gifti.py", line 680, in to_xml
    """ + xml.XmlSerializable.to_xml(self, enc)
  File "/home/yoh/proj/nipy/nipy-suite/nibabel/nibabel/xmlutils.py", line 30, in to_xml
    return tostring(self._to_xml_element(), enc)
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 1126, in tostring
    ElementTree(element).write(file, encoding, method=method)
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 820, in write
    serialize(write, self._root, encoding, qnames, namespaces)
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 939, in _serialize_xml
    _serialize_xml(write, e, encoding, qnames, None)
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 932, in _serialize_xml
    v = _escape_attrib(v, encoding)
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 1092, in _escape_attrib
    _raise_serialization_error(text)
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 1052, in _raise_serialization_error
    "cannot serialize %r (type %s)" % (text, type(text).__name__)
TypeError: cannot serialize 0 (type int)

which happens due to "rogue" ExternalFileOffset being an int, not serialized to str

899     def _serialize_xml(write, elem, encoding, qnames, namespaces):
900         tag = elem.tag
901         text = elem.text
902         if tag is Comment:
903             write("<!--%s-->" % _encode(text, encoding))
904         elif tag is ProcessingInstruction:
905             write("<?%s?>" % _encode(text, encoding))
(Pdb) 
906         else:
907             tag = qnames[tag]
908             if tag is None:
909                 if text:
910                     write(_escape_cdata(text, encoding))
911                 for e in elem:
912                     _serialize_xml(write, e, encoding, qnames, None)
913             else:
914                 write("<" + tag)
915                 items = elem.items()
916                 if items or namespaces:
(Pdb) 
917                     if namespaces:
918                         for v, k in sorted(namespaces.items(),
919                                            key=lambda x: x[1]):  # sort on prefix
920                             if k:
921                                 k = ":" + k
922                             write(" xmlns%s=\"%s\"" % (
923                                 k.encode(encoding),
924                                 _escape_attrib(v, encoding)
925                                 ))
926                     for k, v in sorted(items):  # lexical order
927                         if isinstance(k, QName):
(Pdb) 
928                             k = k.text
929                         if isinstance(v, QName):
930                             v = qnames[v.text]
931                         else:
932  ->                         v = _escape_attrib(v, encoding)
933                         write(" %s=\"%s\"" % (qnames[k], v))
934                 if text or len(elem):
935                     write(">")
936                     if text:
937                         write(_escape_cdata(text, encoding))
938                     for e in elem:
(Pdb) p elem
<Element 'DataArray' at 0x7fd24f50de90>
*(Pdb) p elem.tag
'DataArray'
*(Pdb) p elem.text
None
(Pdb) p namespaces
None
(Pdb) p items
[('Dimensionality', '2'), ('ExternalFileName', ''), ('Encoding', 'GZipBase64Binary'), ('DataType', 'NIFTI_TYPE_FLOAT32'), ('ArrayIndexingOrder', 'RowMajorOrder'), ('ExternalFileOffset', 0), ('Dim0', '4'), ('Dim1', '3'), ('Intent', 'NIFTI_INTENT_POINTSET'), ('Endian', 'LittleEndian')]

[matthew-brett]

Check out fix in #470?