Le Mon, 20 Apr 2009 10:46:47 -0400,
Matt <hellzfury+pyt...@gmail.com> s'exprima ainsi:
> Hey everyone,
>
> I'm hoping someone here can help me solve an odd problem (bug?). I'm having
> trouble with string encoding, object deletion, and the xml.etree library. If
> this isn't the right list to be posting this question, please let me know.
> I'm new to Python and don't know of any other "help me" Python mailing
> lists. I have tried debugging this ad-infinitem. Anyway, at the bottom of
> this e-mail you will find the code of a python file. This is a gross
> over-simplification of my code, with little exception handling so that the
> errors are obvious.
>
> Running this interactively, if you finish off with 'del db', it exits fine
> and creates a skeleton xml file called 'db.xml' with text '<root />'.
> However, if you instead CTRL-D, it throws at exception while quitting and
> then leaves an empty 'db.xml' which won't work. Can anyone here help me
> figure out why this is?
>
> Stuff I've done:
> I've traced this down to the self.commit() call in __del__. The stacktrace
> and a few print statements injected into xml.etree leads me to the call
> 'root'.encode('us-ascii') throwing a LookupError on line 751 of
> xml.etree.ElementTree. This makes no sense to me, since it works fine
> normally.
>
> Thank you very much. Any and all help or pointers are appreciated.
>
> ~Matt
>
> #### db.py ###
> from xml.etree import ElementTree as ET
> import os
>
> class Database(object):
> def __init__(self, path):
> self.__dbpath = path ## Path to the database
> self.load()
> def __del__(self):
> ## FIXME: Known bug:
> ## del db at command line works properly
> ## Ctrl-D, when there is no db file present, results in a
> LookupError
> ## and empty xml file
> from StringIO import StringIO
> from traceback import print_exc
> trace = StringIO()
> try:
> print 5
> self.commit()
> print 7
> except Exception:
> print_exc(100, trace)
> print trace.getvalue()
> def load(self):
> if os.path.exists(self.__dbpath):
> self.root = ET.parse(self.__dbpath).getroot()
> else:
> self.root = ET.Element("root")
> def commit(self):
> ET.ElementTree(self.root).write(self.__dbpath)
> db = Database('db.xml')
Actually, it all runs well for me -- after the following modification:
def __del__(self):
## FIXME: Known bug:
## del db at command line works properly
## Ctrl-D, when there is no db file present, results in a LookupError
## and empty xml file
try:
print 5
self.commit()
print 7
except Exception:
raise
Notes:
* I don't know for what reason you needed such a complicated traceback
construct.
* Before I did this modif, I indeed had a weird exception about stringIO.
* __del__() seems to do the contrary: it writes back to file through commit()???
* "del db" works fine, anyway
* When I run without any bd.xml, it properly creates one with text "<root />".
* When I run with an ampty db.xml, I have the following exception message:
Traceback (most recent call last):
File "xmlTree.py", line 29, in <module>
db = Database('db.xml')
File "xmlTree.py", line 10, in __init__
self.load()
File "xmlTree.py", line 24, in load
self.root = ET.parse(self.__dbpath).getroot()
File "/usr/lib/python2.5/xml/etree/ElementTree.py", line 862, in parse
tree.parse(source, parser)
File "/usr/lib/python2.5/xml/etree/ElementTree.py", line 587, in parse
self._root = parser.close()
File "/usr/lib/python2.5/xml/etree/ElementTree.py", line 1254, in close
self._parser.Parse("", 1) # end of data
xml.parsers.expat.ExpatError: no element found: line 2, column 0
5
Exception exceptions.AttributeError: AttributeError("'Database' object has no
attribute 'root'",) in <bound method Database.__del__ of <__main__.Database
object at 0xb7e78fec>> ignored
------
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