patrick vrijlandt added the comment:
Dear Eli,
According to the XPath spec, the 'position' as can be used in xpath
expressions, should be positive. However, the current implementation (example
below from 3.3.0) accepts some values that should not be ok.
Therefore, I do not agree that it behaves correctly. Garbage positions should
return [] or an exception, not a value. And if you accept one value before the
first position, you should accept them all.
DATA = '''<?xml version="1.0"?>
<data>
<country name="Liechtenstein">
<rank updated="yes">2</rank>
<year>2008</year>
<gdppc>141100</gdppc>
<neighbor name="Austria" direction="E"/>
<neighbor name="Switzerland" direction="W"/>
</country>
<country name="Singapore">
<rank updated="yes">5</rank>
<year>2011</year>
<gdppc>59900</gdppc>
<neighbor name="Malaysia" direction="N"/>
</country>
<country name="Panama">
<rank updated="yes">69</rank>
<year>2011</year>
<gdppc>13600</gdppc>
<neighbor name="Costa Rica" direction="W"/>
<neighbor name="Colombia" direction="E"/>
</country>
</data>
'''
import xml.etree.ElementTree as ET
root = ET.XML(DATA)
print(root)
for XP in (['./country'] +
['./country[%d]' % i for i in range(-1, 5)] +
['./country[last()%+d]' % i for i in range(-3, 5)]):
print('{:20}'.format(XP), [elem.get('name') for elem in root.findall(XP)])
## OUTPUT:
## <Element 'data' at 0x03CD9BD0>
## ./country ['Liechtenstein', 'Singapore', 'Panama']
## ./country[-1] []
## ./country[0] ['Panama']
## ./country[1] ['Liechtenstein']
## ./country[2] ['Singapore']
## ./country[3] ['Panama']
## ./country[4] []
## ./country[last()-3] []
## ./country[last()-2] ['Liechtenstein']
## ./country[last()-1] ['Singapore']
## ./country[last()+0] ['Panama']
## ./country[last()+1] ['Liechtenstein']
## ./country[last()+2] ['Singapore']
## ./country[last()+3] ['Panama']
## ./country[last()+4] []
----------
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<http://bugs.python.org/issue12323>
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