[Tutor] Pickling

[Suzanne Little]

Hello,

I'm trying to use pickle to store a DOM (from xml.dom.minidom). It appears
to perform the dump fine but I can't load the object. Is this because
minidom doesn't support pickling? Or am I mis-understanding something
about the way pickling works?

According to the Library Reference attempts to pickle an unpicklable
object will result in a PicklingError exception but I'm not getting this.
Sample session follows:

Python 2.0 (#1, Feb 14 2001, 10:51:28)
[GCC 2.95.2 19991024 (release)] on sunos5
Type "copyright", "credits" or "license" for more information.
>>> from xml.dom.minidom import parse
>>> import pickle
>>> f = open('pickleTest', 'w')
>>> d = parse('xmlTest.xml')
>>> pickle.dump(d, f)
>>>
$ python2.0
Python 2.0 (#1, Feb 14 2001, 10:51:28)
[GCC 2.95.2 19991024 (release)] on sunos5
Type "copyright", "credits" or "license" for more information.
>>> import pickle
>>> f = open('xmlTest.xml', 'r')
>>> pickle.load(f)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 896, in
load
    return Unpickler(file).load()
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 516, in
load
    dispatch[key](self)
KeyError: <
>>>

Okay. Sometimes I get a blank line and nothing listed for the KeyError.
The xmlTest.xml file is listed below. I'm using python 2.0 on a solaris.

xmlTest.xml:
<?xml version="1.0"?>
<parent id="top"><child1 name="paul">Text goes here</child1>
<child2 name="fred">More text</child2>
</parent>
---

I have also had a few doms not pickle with the following error. There's a
lot more (it shoots up the screen) but here's the last bit. Notably the
xml that this dom was based on was a lot bigger and more complicated than
xmlTest

  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 202, in
save
    f(self, object)
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 433, in
save_inst
    save(stuff)
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 202, in
save
    f(self, object)
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 382, in
save_dict
    save(value)
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 202, in
save
    f(self, object)
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 433, in
save_inst
    save(stuff)
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 202, in
save
    f(self, object)
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 381, in
save_dict
    save(key)
  File "/usr/local/stow/python-2.0/lib/python2.0/pickle.py", line 128, in
save
    pid = self.persistent_id(object)
RuntimeError: Maximum recursion depth exceeded
>>>


Thanks as always,
Suzanne

BTW: Isn't pickle a great name! :) "What are you doing?" "I'm trying to
pickle my doms"

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it were so, it would be; but as it isn't, it ain't.  That's logic"
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