OrderedDict

[Peter Otten]

Chris Angelico wrote:

> On Wed, May 18, 2016 at 7:28 PM, Peter Otten <__peter__ at web.de> wrote:
>> I don't see an official way to pass a custom dict type to the library,
>> but if you are not afraid to change its source code the following patch
>> will allow you to access the value of dictionaries with a single entry as
>> d[0]:
>>
>> $ diff -u py2b_xmltodict/local/lib/python2.7/site-packages/xmltodict.py
>> py2_xmltodict/local/lib/python2.7/site-packages/xmltodict.py
>> --- py2b_xmltodict/local/lib/python2.7/site-packages/xmltodict.py      
>> 2016-05-18 11:18:44.000000000 +0200
>> +++ py2_xmltodict/local/lib/python2.7/site-packages/xmltodict.py       
>> 2016-05-18 11:11:13.417665697 +0200 @@ -35,6 +35,13 @@
>>  __version__ = '0.10.1'
>>  __license__ = 'MIT'
>>
>> +_OrderedDict = OrderedDict
>> +class OrderedDict(_OrderedDict):
>> +    def __getitem__(self, key):
>> +        if key == 0:
>> +            [result] = self.values()
>> +            return result
>> +        return _OrderedDict.__getitem__(self, key)
>>
>>  class ParsingInterrupted(Exception):
>>      pass
> 
> Easier than patching might be monkeypatching.
> 
> class OrderedDict(OrderedDict):
>     ... getitem code as above ...
> xmltodict.OrderedDict = OrderedDict
> 
> Try it, see if it works.

It turns out I was wrong on (at least) two accounts: 

- xmltodict does offer a way to specify the dict type
- the proposed dict implementation will not solve the OP's problem

Here is an improved fix which should work:


$ cat sample.xml 
<?xml version="1.0" encoding="utf-8" ?>
<profiles>
  <profile id='visio02' revision='2015051501' >
  <package package-id='0964-gpg4win' />
  </profile>
</profiles>
$ cat sample2.xml 
<?xml version="1.0" encoding="utf-8" ?>
<profiles>
  <profile id='visio02' revision='2015051501' >
  <package package-id='0964-gpg4win' />
  <package package-id='0965-gpg4win' />
  </profile>
</profiles>
$ cat demo.py
import collections
import sys
import xmltodict


class MyOrderedDict(collections.OrderedDict):
    def __getitem__(self, key):
        if key == 0 and len(self) == 1:
            return self
        return super(MyOrderedDict, self).__getitem__(key)


def main():
    filename = sys.argv[1]
    with open(filename) as f:
        doc = xmltodict.parse(f.read(), dict_constructor=MyOrderedDict)

    print "doc:\n{}\n".format(doc)
    print "package-id: {}".format(
        doc['profiles']['profile']['package'][0]['@package-id'])


if __name__ == "__main__":
    main()
$ python demo.py sample.xml 
doc:
MyOrderedDict([(u'profiles', MyOrderedDict([(u'profile', 
MyOrderedDict([(u'@id', u'visio02'), (u'@revision', u'2015051501'), 
(u'package', MyOrderedDict([(u'@package-id', u'0964-gpg4win')]))]))]))])

package-id: 0964-gpg4win
$ python demo.py sample2.xml 
doc:
MyOrderedDict([(u'profiles', MyOrderedDict([(u'profile', 
MyOrderedDict([(u'@id', u'visio02'), (u'@revision', u'2015051501'), 
(u'package', [MyOrderedDict([(u'@package-id', u'0964-gpg4win')]), 
MyOrderedDict([(u'@package-id', u'0965-gpg4win')])])]))]))])

package-id: 0964-gpg4win