[BangPypers] (no subject)

[Dhananjay Nene]

On Tue, Sep 24, 2013 at 5:48 PM, Vineet Naik <naikvin at gmail.com> wrote:
> Hi,
>
> On Tue, Sep 24, 2013 at 10:38 AM, bab mis <babmis at outlook.com> wrote:
>
>> Hi ,Any XML parser which gives the same kind of data structure as yaml
>> parser gives in python.  Tried with xmlmindom but ir's not of a proper
>> datastrucure ,every time i need to read by element and create the dict.
>>
>
> You can try xmltodict[1]. It also retains the node attributes and makes
> than accessible using the '@' prefix (See the example in README of the repo)
>
> [1]: https://github.com/martinblech/xmltodict

Being curious I immediately took a look and tried the following :

import xmltodict

doc1 = xmltodict.parse("""
<mydocument has="an attribute">
  <and>
    <many>elements</many>
    <many>more elements</many>
  </and>
  <plus a="complex">
    element as well
  </plus>
</mydocument>
""")

doc2 = xmltodict.parse("""
<mydocument has="an attribute">
  <and>
    <many>more elements</many>
  </and>
  <plus a="complex">
    element as well
  </plus>
</mydocument>
""")
print(doc1['mydocument']['and'])
print(doc2['mydocument']['and'])

The output was :
OrderedDict([(u'many', [u'elements', u'more elements'])])
OrderedDict([(u'many', u'more elements')])

The only difference is there is only one "many" node inside the "and"
node in doc2. Do you see an issue here (at least I do). The output
structure is a function of the cardinality of the inner nodes. Since
it changes shape from a list of many to not a list of 1 but just 1
element (throwing away the list). Which can make things rather
unpredictable. Since you cannot predict upfront whether the existence
of just one node inside a parent node is consistent with the xml
schema or is just applicable in that particular instance.

I do think the problem is tractable so long as one clearly documents
the specific constraints which the underlying XML will satisfy,
constraints which will allow transformations to lists or dicts safe.
Trying to make it easy without clearly documenting the constraints
could lead to violations of the principle of least surprise like
above.

>
>
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>
>
>
> --
> Vineet Naik
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