Can I get JSON to load into an OrderedDict

Question

Ok so I can use an OrderedDict in json dump  That is  an OrderedDict can be used as an input to JSON   But can it be used as an output  If so how  In my case I d like to load into an OrderedDict so I can keep the order of the keys in the file   If not  is there some kind of workaround

User · Answer

The normally used load command will work if you specify the object pairs hook parameter   import json from  collections import OrderedDict with open  foo json    r   as fp      metrics types   json load fp  object pairs hook OrderedDict

User · Answer

Yes  you can   By specifying the object pairs hook argument to JSONDecoder   In fact  this is the exact example given in the documentation    gt  gt  gt  json JSONDecoder object pairs hook collections OrderedDict  decode    foo  1   bar   2    OrderedDict    foo   1     bar   2     gt  gt  gt     You can pass this parameter to json loads  if you don t need a Decoder instance for other purposes  like so    gt  gt  gt  import json  gt  gt  gt  from collections import OrderedDict  gt  gt  gt  data   json loads    foo  1   bar   2    object pairs hook OrderedDict   gt  gt  gt  print json dumps data  indent 4         foo   1       bar   2    gt  gt  gt     Using json load is done in the same way    gt  gt  gt  data   json load open  config json    object pairs hook OrderedDict

User · Answer

In addition to dumping the ordered list of keys alongside the dictionary  another low-tech solution  which has the advantage of being explicit  is to dump the  ordered  list of key-value pairs ordered dict items    loading is a simple OrderedDict  lt list of key-value pairs gt    This handles an ordered dictionary despite the fact that JSON does not have this concept  JSON dictionaries have no order    It is indeed nice to take advantage of the fact that json dumps the OrderedDict in the correct order  However  it is in general unnecessarily heavy and not necessarily meaningful to have to read all JSON dictionaries as an OrderedDict  through the object pairs hook argument   so an explicit conversion of only the dictionaries that must be ordered makes sense too

User · Answer

Some great news  Since version 3 6 the cPython implementation has preserved the insertion order of dictionaries  https   mail python org pipermail python-dev 2016-September 146327 html   This means that the json library is now order preserving by default  Observe the difference in behaviour between python 3 5 and 3 6  The code   import json data   json loads    foo  1   bar  2   fiddle    bar  2   foo  1     print json dumps data  indent 4     In py3 5 the resulting order is undefined          fiddle              bar   2           foo   1             bar   2       foo   1     In the cPython implementation of python 3 6          foo   1       bar   2       fiddle              bar   2           foo   1           The really great news is that this has become a language specification as of python 3 7  as opposed to an implementation detail of cPython 3 6    https   mail python org pipermail python-dev 2017-December 151283 html  So the answer to your question now becomes  upgrade to python 3 6

User · Answer

Simple version for Python 2 7   my ordered dict   json loads json str  object pairs hook collections OrderedDict    Or for Python 2 4 to 2 6  import simplejson as json import ordereddict  my ordered dict   json loads json str  object pairs hook ordereddict OrderedDict

User · Answer

You could always write out the list of keys in addition to dumping the dict  and then reconstruct the OrderedDict by iterating through the list

[python] Can I get JSON to load into an OrderedDict?

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