Deserialize a json string to an object in python

Question

I have the following string     action   print   method   onData   data   Madan Mohan     I Want to deserialize to a object of class   class payload     string action     string method     string data   I am using python 2 6 and 2 7

User · Answer

There are different methods to deserialize json string to an object. All above methods are acceptable but I suggest using a library to prevent duplicate key issues or serializing/deserializing of nested objects.

Pykson, is a JSON Serializer and Deserializer for Python which can help you achieve. Simply define Payload class model as JsonObject then use Pykson to convert json string to object.

from pykson import Pykson, JsonObject, StringField

class Payload(pykson.JsonObject):
    action = StringField()
    method = StringField()
    data = StringField()

json_text = '{"action":"print","method":"onData","data":"Madan Mohan"}'
payload = Pykson.from_json(json_text, Payload)

User · Answer

If you want to save lines of code and leave the most flexible solution  we can deserialize the json string to a dynamic object   p   lambda None p   dict     json loads    action    print    method    onData    data    Madan Mohan             p action   output  u print         p method output  u onData

User · Answer

Another way is to simply pass the json string as a dict to the constructor of your object  For example your object is   class Payload object       def   init   self  action  method  data   args    kwargs           self action   action         self method   method         self data   data   And the following two lines of python code will construct it   j   json loads yourJsonString  payload   Payload   j    Basically  we first create a generic json object from the json string  Then  we pass the generic json object as a dict to the constructor of the Payload class  The constructor of Payload class interprets the dict as keyword arguments and sets all the appropriate fields

User · Answer

gt  gt  gt  j      action    print    method    onData    data    Madan Mohan     gt  gt  gt  import json  gt  gt  gt    gt  gt  gt  class Payload object           def   init   self  j               self   dict     json loads j        gt  gt  gt  p   Payload j   gt  gt  gt   gt  gt  gt  p action  print   gt  gt  gt  p method  onData   gt  gt  gt  p data  Madan Mohan

User · Answer

While Alex s answer points us to a good technique  the implementation that he gave runs into a problem when we have nested objects   class more info     string status  class payload     string action     string method     string data     class more info   with the below code   def as more info dct       return MoreInfo dct  status     def as payload dct       return Payload dct  action    dct  method    dct  data    as more info dct  more info      payload   json loads message  object hook   as payload    payload more info will also be treated as an instance of payload which will lead to parsing errors   From the official docs      object hook is an optional function that will be called with the result of any object literal decoded  a dict   The return value of object hook will be used instead of the dict    Hence  I would prefer to propose the following solution instead   class MoreInfo object       def   init   self  status           self status   status       staticmethod     def fromJson mapping           if mapping is None              return None          return MoreInfo              mapping get  status              class Payload object       def   init   self  action  method  data  more info           self action   action         self method   method         self data   data         self more info   more info       staticmethod     def fromJson mapping           if mapping is None              return None          return Payload              mapping get  action                mapping get  method                mapping get  data                MoreInfo fromJson mapping get  more info               import json def toJson obj    kwargs       return json dumps obj  default lambda j  j   dict      kwargs   def fromJson msg  cls    kwargs       return cls fromJson json loads msg    kwargs    info   MoreInfo  ok   payload   Payload  print    onData    better solution   info  pl json   toJson payload  l1   fromJson pl json  Payload

User · Answer

You can specialize an encoder for object creation  http   docs python org 2 library json html  import json class ComplexEncoder json JSONEncoder       def default self  obj           if isinstance obj  complex               return   real   obj real               imag   obj imag                 class      complex           return json JSONEncoder default self  obj   print json dumps 2   1j  cls ComplexEncoder

User · Answer

To elaborate on Sami s answer   From the docs   class Payload object       def   init   self  action  method  data           self action   action         self method   method         self data   data  import json  def as payload dct       return Payload dct  action    dct  method    dct  data     payload   json loads message  object hook   as payload    My objection to the      dict      solution is that while it does the job and is concise  the Payload class becomes totally generic - it doesn t document its fields    For example  if the Payload message had an unexpected format  instead of throwing a key not found error when the Payload was created  no error would be generated until the payload was used

User · Answer

If you are embracing the type hints in Python 3 6  you can do it like this   def from json data  cls       annotations  dict   cls   annotations   if hasattr cls     annotations     else None     if issubclass cls  List           list type   cls   args   0          instance  list   list           for value in data              instance append from json value  list type           return instance     elif issubclass cls  Dict               key type   cls   args   0              val type   cls   args   1              instance  dict   dict               for key  value in data items                    instance update from json key  key type   from json value  val type               return instance     else          instance   cls   cls           for name  value in data items                field type   annotations get name              if inspect isclass field type  and isinstance value   dict  tuple  list  set  frozenset                    setattr instance  name  from json value  field type               else                  setattr instance  name  value          return instance   Which then allows you do instantiate typed objects like this   class Bar      value   int  class Foo      x   int     bar   List Bar    obj   Foo   from json json loads    x   123   bar     value   3     value   2     value   1       Foo  print obj x  print obj bar 2  value    This syntax requires Python 3 6 though and does not cover all cases - for example  support for typing Any    But at least it does not pollute the classes that need to be deserialized with extra init tojson methods

User · Answer

In recent versions of python  you can use marshmallow-dataclass   from marshmallow dataclass import dataclass   dataclass class Payload     action str     method str     data str  Payload Schema   load   action   print   method   onData   data   Madan Mohan

User · Answer

I thought I lose all my hairs for solving this  challenge   I faced following problems    How to deserialize nested objects  lists etc  I like constructors with specified fields I don t like dynamic fields I don t like hacky solutions   I found a library called jsonpickle which is has proven to be really useful    Installation   pip install jsonpickle   Here is a code example with writing nested objects to file   import jsonpickle   class SubObject      def   init   self  sub name  sub age           self sub name   sub name         self sub age   sub age   class TestClass       def   init   self  name  age  sub object           self name   name         self age   age         self sub object   sub object   john junior   SubObject  John jr    2   john   TestClass  John   21  john junior   file name    JohnWithSon      json   john string   jsonpickle encode john   with open file name   w   as fp      fp write john string   john from file   open file name  read    test class 2   jsonpickle decode john from file   print test class 2 name  print test class 2 age  print test class 2 sub object sub name    Output   John 21 John jr    Website  http   jsonpickle github io   Hope it will save your time  and hairs

User · Answer

pydantic is an increasingly popular library for python 3 6  projects  It mainly does data validation and settings management using type hints  A basic example using different types  from pydantic import BaseModel  class ClassicBar BaseModel       count drinks  int     is open  bool   data     count drinks    226    is open    False   cb   ClassicBar   data   gt  gt  gt  cb ClassicBar count drinks 226  is open False   What I love about the lib is that you get a lot of goodies for free  like  gt  gt  gt  cb json      quot count drinks quot   226   quot is open quot   false    gt  gt  gt  cb dict     count drinks   226   is open   False

User · Answer

I prefer to add some checking of the fields  e g  so you can catch errors like when you get invalid json  or not the json you were expecting  so I used namedtuples   from collections import namedtuple payload   namedtuple  payload     action    method    data    def deserialize payload json       kwargs    dict   field  json field   for field in payload  fields        return payload   kwargs    this will let give you nice errors when the json you are parsing does not match the thing you want it to parse   gt  gt  gt  json     action   print   method   onData   data   Madan Mohan    gt  gt  gt  deserialize payload json  payload action  print   method  onData   data  Madan Mohan    gt  gt  gt  badjson     error   404   info   page not found    gt  gt  gt  deserialize payload badjson  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 2  in deserialize payload KeyError   action    if you want to parse nested relations  e g     parent    child    name   henry      you can still use the namedtuples  and even a more reusable function  Person   namedtuple  Person     parent    Parent   namedtuple  Parent     child    Child   namedtuple  Child     name    def deserialize json to namedtuple json  namedtuple       return namedtuple   dict   field  json field   for field in namedtuple  fields     def deserialize person json        json  parent    child      deserialize json to namedtuple json  parent    child    Child       json  parent      deserialize json to namedtuple json  parent    Parent        person   deserialize json to namedtuple json  Person       return person   giving  you   gt  gt  gt  deserialize person   parent    child    name   henry      Person parent Parent child Child name  henry      gt  gt  gt  deserialize person   error   404   info   page not found    Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 2  in deserialize person KeyError   parent

[python] Deserialize a json string to an object in python

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