How to make a class JSON serializable

Question

How to make a Python class serializable     A simple class   class FileItem      def   init   self  fname           self fname   fname   What should I do to be able to get output of    gt  gt  gt  import json   gt  gt  gt  my file   FileItem   foo bar    gt  gt  gt  json dumps my file  TypeError  Object of type  FileItem  is not JSON serializable   Without the error

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I see no mention here of serial versioning or backcompat, so I will post my solution which I've been using for a bit. I probably have a lot more to learn from, specifically Java and Javascript are probably more mature than me here but here goes

https://gist.github.com/andy-d/b7878d0044a4242c0498ed6d67fd50fe

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jsonweb seems to be the best solution for me  See http   www jsonweb info en latest   from jsonweb encode import to object  dumper   to object   class DataModel object     def   init   self  id  value      self id   id    self value   value   gt  gt  gt  data   DataModel 5   foo    gt  gt  gt  dumper data       type      DataModel    id   5   value    foo

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jaraco gave a pretty neat answer  I needed to fix some minor things  but this works   Code    Your custom class class MyCustom object       def   json   self           return                a   self a               b   self b                 python      mymodule submodule MyCustom from json                  to json     json      supported by simplejson       classmethod     def from json cls  json           obj   cls           obj a   json  a           obj b   json  b           return obj    Dumping and loading import simplejson  obj   MyCustom   obj a   3 obj b   4  json   simplejson dumps obj  for json True     Two-step loading obj2 dict   simplejson loads json  obj2   MyCustom from json obj2 dict     Make sure we have the correct thing assert isinstance obj2  MyCustom  assert obj2   dict      obj   dict     Note that we need two steps for loading  For now  the   python   property is not used   How common is this   Using the method of AlJohri  I check popularity of approaches   Serialization  Python -  JSON     to json  266 595 on 2018-06-27 toJSON  96 307 on 2018-06-27   json    8 504 on 2018-06-27 for json  6 937 on 2018-06-27   Deserialization  JSON -  Python     from json  226 101 on 2018-06-27

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This has worked well for me    class JsonSerializable object        def serialize self           return json dumps self   dict         def   repr   self           return self serialize         staticmethod     def dumper obj           if  serialize  in dir obj               return obj serialize            return obj   dict     and then  class FileItem JsonSerializable             and  log debug json dumps  lt my object gt   default JsonSerializable dumper  indent 2

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Here is my 3 cents     This demonstrates explicit json serialization for a tree-like python object  Note  If you actually wanted some code like this you could use the twisted  FilePath class   import json  sys  os  class File      def   init   self  path           self path   path      def isdir self           return os path isdir self path       def isfile self           return os path isfile self path       def children self                   return  File os path join self path  f                    for f in os listdir self path        def getsize self                   return os path getsize self path       def getModificationTime self           return os path getmtime self path   def  default o       d          d  path     o path     d  isFile     o isfile       d  isDir     o isdir       d  mtime     int o getModificationTime        d  size     o getsize   if o isfile   else 0     if o isdir    d  children     o children       return d  folder   os path abspath      json dump File folder   sys stdout  default  default

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For more complex classes you could consider the tool jsonpickle   jsonpickle is a Python library for serialization and deserialization of complex Python objects to and from JSON  The standard Python libraries for encoding Python into JSON  such as the stdlib   s json  simplejson  and demjson  can only handle Python primitives that have a direct JSON equivalent  e g  dicts  lists  strings  ints  etc    jsonpickle builds on top of these libraries and allows more complex data structures to be serialized to JSON  jsonpickle is highly configurable and extendable   allowing the user to choose the JSON backend and add additional backends    link to jsonpickle on PyPi

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As mentioned in many other answers you can pass a function to json dumps to convert objects that are not one of the types supported by default to a supported type  Surprisingly none of them mentions the simplest case  which is to use the built-in function vars to convert objects into a dict containing all their attributes  json dumps obj  default vars   Note that this covers only basic cases  if you need more specific serialization for certain types  e g  exluding certain attributes or objects that don t have a   dict   attribute  you need to use a custom function or a JSONEncoder as desribed in the other answers

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If you don t mind installing a package for it  you can use json-tricks   pip install json-tricks   After that you just need to import dump s  from json tricks instead of json  and it ll usually work   from json tricks import dumps json str   dumps cls instance  indent 4    which ll give               instance type                        module name test class                    MyTestCls                      attributes                      attr    val                    dct attr                              hello   42                                 And that s basically it     This will work great in general  There are some exceptions  e g  if special things happen in   new    or more metaclass magic is going on   Obviously loading also works  otherwise what s the point    from json tricks import loads json str   loads json str    This does assume that module name test class MyTestCls can be imported and hasn t changed in non-compatible ways  You ll get back an instance  not some dictionary or something  and it should be an identical copy to the one you dumped   If you want to customize how something gets  de serialized  you can add special methods to your class  like so   class CustomEncodeCls          def   init   self                   self relevant   42                 self irrelevant   37          def   json encode   self                     should return primitive  serializable types like dict  list  int  string  float                    return   relevant   self relevant           def   json decode   self    attrs                     should initialize all properties  note that   init   is not called implicitly                 self relevant   attrs  relevant                   self irrelevant   12   which serializes only part of the attributes parameters  as an example   And as a free bonus  you get  de serialization of numpy arrays  date  amp  times  ordered maps  as well as the ability to include comments in json   Disclaimer  I created json tricks  because I had the same problem as you

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This class can do the trick  it converts object to standard json    import json   class Serializer object        staticmethod     def serialize object           return json dumps object  default lambda o  o   dict   values   0     usage   Serializer serialize my object    working in python2 7 and python3

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First we need to make our object JSON-compliant  so we can dump it using the standard JSON module  I did it this way   def serialize o       if isinstance o  dict           return  k serialize v  for k v in o items        if isinstance o  list           return  serialize e  for e in o      if isinstance o  bytes           return o decode  utf-8       return o

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I ran into this problem when I tried to store Peewee s model into PostgreSQL JSONField   After struggling for a while  here s the general solution   The key to my solution is going through Python s source code and realizing that the code documentation  described here  already explains how to extend the existing json dumps to support other data types   Suppose you current have a model that contains some fields that are not serializable to JSON and the model that contains the JSON field originally looks like this   class SomeClass Model       json field   JSONField     Just define a custom JSONEncoder like this   class CustomJsonEncoder json JSONEncoder       def default self  obj           if isinstance obj  SomeTypeUnsupportedByJsonDumps               return  lt  whatever value you want  gt          return json JSONEncoder default self  obj        staticmethod     def json dumper obj           return json dumps obj  cls CustomJsonEncoder    And then just use it in your JSONField like below   class SomeClass Model       json field   JSONField dumps CustomJsonEncoder json dumper    The key is the default self  obj  method above  For every single     is not JSON serializable complaint you receive from Python  just add code to handle the unserializable-to-JSON type  such as Enum or datetime   For example  here s how I support a class inheriting from Enum   class TransactionType Enum      CURRENT   1    STACKED   2     def default self  obj          if isinstance obj  TransactionType              return obj value        return json JSONEncoder default self  obj    Finally  with the code implemented like above  you can just convert any Peewee models to be a JSON-seriazable object like below   peewee model   WhateverPeeweeModel   new model   SomeClass   new model json field   model to dict peewee model    Though the code above was  somewhat  specific to Peewee  but I think    It s applicable to other ORMs  Django  etc  in general Also  if you understood how json dumps works  this solution also works with Python  sans ORM  in general too   Any questions  please post in the comments section  Thanks

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There are many approaches to this problem    ObjDict    pip install objdict  is another   There is an emphasis on providing javascript like objects which can also act like dictionaries to best handle data loaded from JSON  but there are other features which can be useful as well   This provides another alternative solution to the original problem

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Do you have an idea about the expected output  For example  will this do    gt  gt  gt  f    FileItem   foo bar    gt  gt  gt  magic f     fname     foo bar      In that case you can merely call json dumps f   dict       If you want more customized output then you will have to subclass JSONEncoder and implement your own custom serialization    For a trivial example  see below    gt  gt  gt  from json import JSONEncoder  gt  gt  gt  class MyEncoder JSONEncoder           def default self  o               return o   dict         gt  gt  gt  MyEncoder   encode f     fname     foo bar      Then you pass this class into the json dumps   method as cls kwarg   json dumps cls MyEncoder    If you also want to decode then you ll have to supply a custom object hook to the JSONDecoder class  For example    gt  gt  gt  def from json json object           if  fname  in json object              return FileItem json object  fname     gt  gt  gt  f   JSONDecoder object hook   from json  decode    fname     foo bar      gt  gt  gt  f  lt   main   FileItem object at 0x9337fac gt   gt  gt  gt

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Kyle Delaney s comment is correct so i tried to use the answer https   stackoverflow com a 15538391 1497139 as well as an improved version of https   stackoverflow com a 10254820 1497139 to create a  quot JSONAble quot  mixin  So to make a class JSON serializeable use  quot JSONAble quot  as a super class and either call   instance toJSON    or  instance asJSON    for the two offered methods  You could also extend the JSONAble class with other approaches offered here  The test example for the Unit Test with Family and Person sample results in  toJSOn           quot members quot              quot Flintstone Fred quot                  quot firstName quot    quot Fred quot                quot lastName quot    quot Flintstone quot                      quot Flintstone Wilma quot                  quot firstName quot    quot Wilma quot                quot lastName quot    quot Flintstone quot                        quot name quot    quot The Flintstones quot     asJSOn      name    The Flintstones    members     Flintstone Fred     firstName    Fred    lastName    Flintstone     Flintstone Wilma     firstName    Wilma    lastName    Flintstone      Unit Test with Family and Person sample def testJsonAble self           family Family  quot The Flintstones quot           family add Person  quot Fred quot   quot Flintstone quot             family add Person  quot Wilma quot   quot Flintstone quot            json1 family toJSON           json2 family asJSON           print json1          print json2   class Family JSONAble       def   init   self name           self name name         self members             def add self person           self members person lastName  quot   quot  person firstName  person  class Person JSONAble       def   init   self firstName lastName           self firstName firstName          self lastName lastName   jsonable py defining JSONAble mixin      Created on 2020-09-03   author  wf     import json  class JSONAble object               mixin to allow classes to be JSON serializable see     https   stackoverflow com questions 3768895 how-to-make-a-class-json-serializable              def   init   self                       Constructor                      def toJSON self           return json dumps self  default lambda o  o   dict                 sort keys True  indent 4               def getValue self v           if  hasattr v   quot asJSON quot                 return v asJSON           elif type v  is dict              return self reprDict v          elif type v  is list              vlist                for vitem in v                  vlist append self getValue vitem               return vlist         else                 return v          def reprDict self srcDict                       get my dict elements                     d   dict           for a  v in srcDict items                d a  self getValue v          return d          def asJSON self                       recursively return my dict elements                     return self reprDict self   dict        You ll find these approaches now integrated in the https   github com WolfgangFahl pyLoDStorage project which is available at https   pypi org project pylodstorage

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In addition to the Onur s answer  You possibly want to deal with datetime type like below   in order to handle   datetime datetime  object has no attribute  dict  exception    def datetime option value       if isinstance value  datetime date           return value timestamp       else          return value   dict     Usage   def toJSON self       return json dumps self  default datetime option  sort keys True  indent 4

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Most of the answers involve changing the call to json dumps    which is not always possible or desirable  it may happen inside a framework component for example    If you want to be able to call  json dumps obj  as is  then a simple solution is inheriting from dict   class FileItem dict       def   init   self  fname           dict   init   self  fname fname   f   FileItem  tasks txt   json dumps f    No need to change anything here   This works if your class is just basic data representation  for trickier things you can always set keys explicitly

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json is limited in terms of objects it can print  and jsonpickle  you may need a pip install jsonpickle  is limited in terms it can t indent text  If you would like to inspect the contents of an object whose class you can t change  I still couldn t find a straighter way than    import json  import jsonpickle       print  json dumps json loads jsonpickle encode object    indent 2    Note  that still they can t print the object methods

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If you re using Python3 5   you could use jsons  It will convert your object  and all its attributes recursively  to a dict   import jsons  a dict   jsons dump your object    Or if you wanted a string   a str   jsons dumps your object    Or if your class implemented jsons JsonSerializable   a dict   your object json

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Another option is to wrap JSON dumping in its own class   import json  class FileItem      def   init   self  fname           self fname   fname      def   repr   self           return json dumps self   dict      Or  even better  subclassing FileItem class from a JsonSerializable class   import json  class JsonSerializable object       def toJson self           return json dumps self   dict         def   repr   self           return self toJson     class FileItem JsonSerializable       def   init   self  fname           self fname   fname   Testing    gt  gt  gt  f   FileItem   foo bar    gt  gt  gt  f toJson      fname     foo bar     gt  gt  gt  f    fname     foo bar     gt  gt  gt  str f    string coercion    fname     foo bar

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class DObject json JSONEncoder       def delete not related keys self   dict           for key in   quot skipkeys quot    quot ensure ascii quot    quot check circular quot    quot allow nan quot    quot sort keys quot    quot indent quot                try                  del  dict key              except                  continue      def default self  o           if hasattr o     dict                  my dict   o   dict   copy               self delete not related keys my dict              return my dict         else              return o  a   DObject   a name    abdul wahid  b   DObject   b name   a  print json dumps b  cls DObject

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Building on Quinten Cabo s answer  def sterilize obj        quot  quot  quot Make an object more ameniable to dumping as json      quot  quot  quot      if type obj  in  str  float  int  bool  type None            return obj     elif isinstance obj  dict           return  k  sterilize v  for k  v in obj items        list ret          dict ret          for a in dir obj           if a       iter    and callable obj   iter                 list ret extend  sterilize v  for v in obj           elif a       dict                 dict ret update  k  sterilize v  for k  v in obj   dict   items   if k not in     module        dict        weakref        doc               elif a not in     doc        module                  aval   getattr obj  a              if type aval  in  str  float  int  bool  type None                    dict ret a    aval             elif a       class    and a       objclass    and isinstance aval  type                   dict ret a    sterilize aval      if len list ret     0          if len dict ret     0              return repr obj          return dict ret     else          if len dict ret     0              return list ret     return  list ret  dict ret   The differences are  Works for any iterable instead of just list and tuple  it works for NumPy arrays  etc   Works for dynamic types  ones that contain a   dict     Includes native types float and None so they don t get converted to string  Classes that have   dict   and members will mostly work  if the   dict   and member names collide  you will only get one - likely the member  Classes that are lists and have members will look like a tuple of the list and a dictionary Python3  that isinstance   call may be the only thing that needs changing

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import json  class Foo object       def   init   self           self bar    baz          self  qux    flub       def somemethod self           pass  def default instance       return  k  v             for k  v in vars instance  items               if not str k  startswith        json foo   json dumps Foo    default default  assert    bar    baz       json foo  print json foo

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To add another option  You can use the attrs package and the asdict method   class ObjectEncoder JSONEncoder       def default self  o           return attr asdict o   json dumps objects  cls ObjectEncoder    and to convert back  def from json o       if   obj name  in o          type    o   obj name           del o   obj name           return globals   type     o      else          return o  data   JSONDecoder object hook from json  decode data    class looks like this   attr s class Foo object       x   attr ib        obj name   attr ib init False  default  Foo

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I like Onur s answer but would expand to include an optional toJSON   method for objects to serialize themselves   def dumper obj       try          return obj toJSON       except          return obj   dict   print json dumps some big object  default dumper  indent 2

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Just add to json method to your class like this   def to json self     return self message   or how you want it to be serialized   And add this code  from this answer   to somewhere at the top of everything   from json import JSONEncoder  def  default self  obj       return getattr obj   class     to json    default default  obj    default default   JSONEncoder   default JSONEncoder default    default   This will monkey-patch json module when it s imported so JSONEncoder default   automatically checks for a special  to json    method and uses it to encode the object if found   Just like Onur said  but this time you don t have to update every json dumps   in your project

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This function uses recursion to iterate over every part of the dictionary and then calls the repr   methods of classes that are not build-in types  def sterilize obj       object type   type obj      if isinstance obj  dict           return  k  sterilize v  for k  v in obj items        elif object type in  list  tuple           return  sterilize v  for v in obj      elif object type in  str  int  bool  float           return obj     else          return obj   repr

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I liked Lost Koder s method the most  I ran into issues when trying to serialize more complex objects whos members methods aren t serializable  Here s my implementation that works on more objects   class Serializer object        staticmethod     def serialize obj           def check o               for k  v in o   dict   items                    try                          json dumps v                      o   dict   k    v                 except TypeError                      o   dict   k    str v              return o         return json dumps check obj    dict    indent 2

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Here is a simple solution for a simple feature   toJSON   Method Instead of a JSON serializable class  implement a serializer method  import json  class Object      def toJSON self           return json dumps self  default lambda o  o   dict                 sort keys True  indent 4   So you just call it to serialize  me   Object   me name    quot Onur quot  me age   35 me dog   Object   me dog name    quot Apollo quot   print me toJSON     will output         quot age quot   35       quot dog quot              quot name quot    quot Apollo quot              quot name quot    quot Onur quot

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I chose to use decorators to solve the datetime object serialization problem  Here is my code    myjson py  Author  jmooremcc 7 16 2017  import json from datetime import datetime  date  time  timedelta     This module uses decorators to serialize date objects using json The filename is myjson py In another module you simply add the following import statement      from myjson import json  json dumps and json dump will then correctly serialize datetime and date  objects      def json serial obj          JSON serializer for objects not serializable by default json code         if isinstance obj   datetime  date            serial   str obj          return serial     raise TypeError   Type  s not serializable    type obj     def FixDumps fn       def hook obj           return fn obj  default json serial       return hook  def FixDump fn       def hook obj  fp           return fn obj fp  default json serial       return hook   json dumps FixDumps json dumps  json dump FixDump json dump    if   name       main         today datetime now       data   atime  today   greet   Hello       str json dumps data      print str   By importing the above module  my other modules use json in a normal way  without specifying the default keyword  to serialize data that contains date time objects  The datetime serializer code is automatically called for json dumps and json dump

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import simplejson  class User object       def   init   self  name  mail           self name   name         self mail   mail      def  asdict self           return self   dict    print simplejson dumps User  alice    alice mail com       if use standard json  u need to define a default function  import json def default o       return o  asdict    print json dumps User  alice    alice mail com    default default

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This is a small library that serializes an object with all its children to JSON and also parses it back  https   github com tobiasholler PyJSONSerialization

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I came across this problem the other day and implemented a more general version of an Encoder for Python objects that can handle nested objects and inherited fields   import json import inspect  class ObjectEncoder json JSONEncoder       def default self  obj           if hasattr obj   to json                return self default obj to json            elif hasattr obj     dict                  d   dict                   key  value                  for key  value in inspect getmembers obj                  if not key startswith                       and not inspect isabstract value                  and not inspect isbuiltin value                  and not inspect isfunction value                  and not inspect isgenerator value                  and not inspect isgeneratorfunction value                  and not inspect ismethod value                  and not inspect ismethoddescriptor value                  and not inspect isroutine value                            return self default d          return obj   Example   class C object       c    NO      def to json self           return   c    YES    class B object       b    B      i    I      def   init   self  y           self y   y      def f self           print  f   class A B       a    A      def   init   self           self b      ab   B  y             self c   C    print json dumps A    cls ObjectEncoder  indent 2  sort keys True    Result        a    A       b                  ab              b    B             i    I             y    y                         c          c    YES           i    I

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If you are able to install a package  I d recommend trying dill  which worked just fine for my project  A nice thing about this package is that it has the same interface as pickle  so if you have already been using pickle in your project you can simply substitute in dill and see if the script runs  without changing any code  So it is a very cheap solution to try    Full anti-disclosure  I am in no way affiliated with and have never contributed to the dill project    Install the package   pip install dill   Then edit your code to import dill instead of pickle     import pickle import dill as pickle   Run your script and see if it works   If it does you may want to clean up your code so that you are no longer shadowing the pickle module name    Some specifics on datatypes that dill can and cannot serialize  from the project page      dill can pickle the following standard types       none  type  bool  int  long  float  complex  str  unicode  tuple    list  dict  file  buffer  builtin  both old and new style classes    instances of old and new style classes  set  frozenset  array    functions  exceptions       dill can also pickle more    exotic    standard types       functions with yields  nested functions  lambdas  cell  method    unboundmethod  module  code  methodwrapper  dictproxy    methoddescriptor  getsetdescriptor  memberdescriptor    wrapperdescriptor  xrange  slice  notimplemented  ellipsis  quit       dill cannot yet pickle these standard types       frame  generator  traceback

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I came up with my own solution  Use this method  pass any document  dict list  ObjectId etc  to serialize   def getSerializable doc         check if it s a list     if isinstance doc  list           for i  val in enumerate doc               doc i    getSerializable doc i           return doc        check if it s a dict     if isinstance doc  dict           for key in doc keys                doc key    getSerializable doc key           return doc        Process ObjectId     if isinstance doc  ObjectId           doc   str doc          return doc        Use any other custom serializting stuff here           For the rest of stuff     return doc

[python] How to make a class JSON serializable

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