16.6. JSON Object

16.6.1. SetUp

>>> from pprint import pprint
>>> from dataclasses import dataclass
>>> import json

16.6.2. Encoder

>>> class User:
...     def __init__(self, firstname, lastname, age=None):
...         self.firstname = firstname
...         self.lastname = lastname
...         self.age = age
...
...     def __repr__(self):
...         clsname = self.__class__.__qualname__
...         arguments = ', '.join(f'{k}={v!r}' for k,v in vars(self).items())
...         return f'{clsname}({arguments})'
>>>
>>> DATA = [
...     User('Alice', 'Apricot', age=30),
...     User('Bob', 'Blackthorn', age=31),
...     User('Carol', 'Corn', age=32),
...     User('Dave', 'Durian', age=33),
...     User('Eve', 'Elderberry', age=34),
...     User('Mallory', 'Melon', age=15),
... ]
>>>
>>> def encoder(obj):
...     cls = obj.__class__
...     clsname = cls.__name__
...     return {'_clsname': clsname} | vars(obj)
>>>
>>>
>>> result = json.dumps(DATA, default=encoder, indent=2)
>>> print(result)
[
  {
    "_clsname": "User",
    "firstname": "Alice",
    "lastname": "Apricot",
    "age": 30
  },
  {
    "_clsname": "User",
    "firstname": "Bob",
    "lastname": "Blackthorn",
    "age": 31
  },
  {
    "_clsname": "User",
    "firstname": "Carol",
    "lastname": "Corn",
    "age": 32
  },
  {
    "_clsname": "User",
    "firstname": "Dave",
    "lastname": "Durian",
    "age": 33
  },
  {
    "_clsname": "User",
    "firstname": "Eve",
    "lastname": "Elderberry",
    "age": 34
  },
  {
    "_clsname": "User",
    "firstname": "Mallory",
    "lastname": "Melon",
    "age": 15
  }
]

16.6.3. Decoder

>>> DATA = """
... [
...   {
...     "_clsname": "User",
...     "firstname": "Alice",
...     "lastname": "Apricot",
...     "age": 30
...   },
...   {
...     "_clsname": "User",
...     "firstname": "Bob",
...     "lastname": "Blackthorn",
...     "age": 31
...   },
...   {
...     "_clsname": "User",
...     "firstname": "Carol",
...     "lastname": "Corn",
...     "age": 32
...   },
...   {
...     "_clsname": "User",
...     "firstname": "Dave",
...     "lastname": "Durian",
...     "age": 33
...   },
...   {
...     "_clsname": "User",
...     "firstname": "Eve",
...     "lastname": "Elderberry",
...     "age": 34
...   },
...   {
...     "_clsname": "User",
...     "firstname": "Mallory",
...     "lastname": "Melon",
...     "age": 15
...   }
... ]
... """

>>> class User:
...     def __init__(self, firstname, lastname, age=None):
...         self.firstname = firstname
...         self.lastname = lastname
...         self.age = age
...
...     def __repr__(self):
...         clsname = self.__class__.__qualname__
...         arguments = ', '.join(f'{k}={v!r}' for k,v in vars(self).items())
...         return f'{clsname}({arguments})'
>>>
>>>
>>> def decoder(obj):
...     clsname = obj.pop('_clsname')
...     cls = globals()[clsname]
...     return cls(**obj)
>>>
>>> json.loads(DATA, object_hook=decoder)
[User(firstname='Alice', lastname='Apricot', age=30),
 User(firstname='Bob', lastname='Blackthorn', age=31),
 User(firstname='Carol', lastname='Corn', age=32),
 User(firstname='Dave', lastname='Durian', age=33),
 User(firstname='Eve', lastname='Elderberry', age=34),
 User(firstname='Mallory', lastname='Melon', age=15)]

16.6.4. Objects with Relations

>>> class User:
...     def __init__(self, firstname, lastname, age=None, groups=None):
...         self.firstname = firstname
...         self.lastname = lastname
...         self.age = age
...         self.groups = groups if groups else []
...
...     def __repr__(self):
...         clsname = self.__class__.__qualname__
...         arguments = ', '.join(f'{k}={v!r}' for k,v in vars(self).items())
...         return f'{clsname}({arguments})'
>>>
>>> class Group:
...     def __init__(self, name):
...         self.name = name
...
...     def __repr__(self):
...         return f'{self.name}'
>>>
>>>
>>> DATA = [
...     User(firstname='Alice', lastname='Apricot', age=30, groups=[
...         Group('users'),
...         Group('staff'),
...     ]),
...
...     User(firstname='Bob', lastname='Blackthorn', age=31, groups=[
...         Group('users'),
...         Group('staff'),
...     ]),
...
...     User(firstname='Carol', lastname='Corn', age=32, groups=[
...         Group('users'),
...     ]),
...
...     User(firstname='Dave', lastname='Durian', age=33, groups=[
...         Group('users'),
...     ]),
...
...     User(firstname='Eve', lastname='Elderberry', age=34, groups=[
...         Group('users'),
...         Group('staff'),
...         Group('admins'),
...     ]),
...
...     User(firstname='Mallory', lastname='Melon', age=15, groups=[]),
... ]

Encoder:

>>> def encoder(obj):
...     cls = obj.__class__
...     clsname = cls.__name__
...     return {'_clsname': clsname} | vars(obj)
>>>
>>>
>>> encoded = json.dumps(DATA, default=encoder, indent=2)
>>> print(encoded)
[
  {
    "_clsname": "User",
    "firstname": "Alice",
    "lastname": "Apricot",
    "age": 30,
    "groups": [
      {
        "_clsname": "Group",
        "name": "users"
      },
      {
        "_clsname": "Group",
        "name": "staff"
      }
    ]
  },
  {
    "_clsname": "User",
    "firstname": "Bob",
    "lastname": "Blackthorn",
    "age": 31,
    "groups": [
      {
        "_clsname": "Group",
        "name": "users"
      },
      {
        "_clsname": "Group",
        "name": "staff"
      }
    ]
  },
  {
    "_clsname": "User",
    "firstname": "Carol",
    "lastname": "Corn",
    "age": 32,
    "groups": [
      {
        "_clsname": "Group",
        "name": "users"
      }
    ]
  },
  {
    "_clsname": "User",
    "firstname": "Dave",
    "lastname": "Durian",
    "age": 33,
    "groups": [
      {
        "_clsname": "Group",
        "name": "users"
      }
    ]
  },
  {
    "_clsname": "User",
    "firstname": "Eve",
    "lastname": "Elderberry",
    "age": 34,
    "groups": [
      {
        "_clsname": "Group",
        "name": "users"
      },
      {
        "_clsname": "Group",
        "name": "staff"
      },
      {
        "_clsname": "Group",
        "name": "admins"
      }
    ]
  },
  {
    "_clsname": "User",
    "firstname": "Mallory",
    "lastname": "Melon",
    "age": 15,
    "groups": []
  }
]

Decoder:

>>> def decoder(obj):
...     clsname = obj.pop('_clsname')
...     cls = globals()[clsname]
...     return cls(**obj)
>>>
>>> json.loads(encoded, object_hook=decoder)
[User(firstname='Alice', lastname='Apricot', age=30, groups=[users, staff]),
 User(firstname='Bob', lastname='Blackthorn', age=31, groups=[users, staff]),
 User(firstname='Carol', lastname='Corn', age=32, groups=[users]),
 User(firstname='Dave', lastname='Durian', age=33, groups=[users]),
 User(firstname='Eve', lastname='Elderberry', age=34, groups=[users, staff, admins]),
 User(firstname='Mallory', lastname='Melon', age=15, groups=[])]

16.6.5. Assignments

# %% About
# - Name: JSON Object Dumps
# - Difficulty: medium
# - Lines: 5
# - Minutes: 5

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% English
# 1. Serialize data from variable `DATA`
# 2. To each row add `_clsname` with an object type name
# 3. Use `json` module
# 4. Result write to variable `result`
# 5. Run doctests - all must succeed

# %% Polish
# 1. Zserializuj dane ze zmiennej `DATA`
# 2. To each row add `_clsname` with an object type name
# 3. Użyj modułu `json`
# 4. Wynik zapisz do zmiennej `result`
# 5. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# ('[{"_clsname": "User", "firstname": "Alice", "lastname": "Apricot", "age": 30, "groups": []}, '
#  '{"_clsname": "User", "firstname": "Bob", "lastname": "Blackthorn", "age": 31, "groups": []}, '
#  '{"_clsname": "User", "firstname": "Carol", "lastname": "Corn", "age": 32, "groups": []}, '
#  '{"_clsname": "User", "firstname": "Dave", "lastname": "Durian", "age": 33, "groups": []}, '
#  '{"_clsname": "User", "firstname": "Eve", "lastname": "Elderberry", "age": 34, "groups": []}, '
#  '{"_clsname": "User", "firstname": "Mallory", "lastname": "Melon", "age": 15, "groups": []}]')

# %% Hints
# - `dict()`
# - `dict.update()`
# - `object.__class__.__name__`

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> assert type(result)

>>> from pprint import pprint
>>> pprint(result, width=100)
('[{"_clsname": "User", "firstname": "Alice", "lastname": "Apricot", "age": 30, "groups": []}, '
 '{"_clsname": "User", "firstname": "Bob", "lastname": "Blackthorn", "age": 31, "groups": []}, '
 '{"_clsname": "User", "firstname": "Carol", "lastname": "Corn", "age": 32, "groups": []}, '
 '{"_clsname": "User", "firstname": "Dave", "lastname": "Durian", "age": 33, "groups": []}, '
 '{"_clsname": "User", "firstname": "Eve", "lastname": "Elderberry", "age": 34, "groups": []}, '
 '{"_clsname": "User", "firstname": "Mallory", "lastname": "Melon", "age": 15, "groups": []}]')
"""

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`

# %% Imports
import json

# %% Types
from typing import Callable
encoder: Callable[[object], dict]
result: str

# %% Data
class User:
    def __init__(self, firstname, lastname, age=None, groups=None):
        self.firstname = firstname
        self.lastname = lastname
        self.age = age
        self.groups = groups if groups else []

    def __repr__(self):
        clsname = self.__class__.__qualname__
        arguments = ', '.join(f'{k}={v!r}' for k,v in vars(self).items())
        return f'{clsname}({arguments})'


DATA = [
    User('Alice', 'Apricot', age=30),
    User('Bob', 'Blackthorn', age=31),
    User('Carol', 'Corn', age=32),
    User('Dave', 'Durian', age=33),
    User('Eve', 'Elderberry', age=34),
    User('Mallory', 'Melon', age=15),
]

# %% Result
result = ...

# %% About
# - Name: JSON Object Dataclass
# - Difficulty: easy
# - Lines: 5
# - Minutes: 5

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% English
# 1. Deserialize data from variable `DATA`
# 2. Use `json` module
# 3. Result write to variable `result`
# 4. Run doctests - all must succeed

# %% Polish
# 1. Zdeserializuj dane ze zmiennej `DATA`
# 2. Użyj modułu `json`
# 3. Wynik zapisz do zmiennej `result`
# 4. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# [User(firstname='Alice', lastname='Apricot', age=30, groups=[]),
#  User(firstname='Bob', lastname='Blackthorn', age=31, groups=[]),
#  User(firstname='Carol', lastname='Corn', age=32, groups=[]),
#  User(firstname='Dave', lastname='Durian', age=33, groups=[]),
#  User(firstname='Eve', lastname='Elderberry', age=34, groups=[]),
#  User(firstname='Mallory', lastname='Melon', age=15, groups=[])]

# %% Hints
# - `dict.pop()`
# - `globals()`
# - `cls(**obj)`

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> type(result)
<class 'list'>

>>> len(result) > 0
True

>>> all(type(row) is User
...     for row in result)
True

>>> from pprint import pprint
>>> pprint(result)
[User(firstname='Alice', lastname='Apricot', age=30, groups=[]),
 User(firstname='Bob', lastname='Blackthorn', age=31, groups=[]),
 User(firstname='Carol', lastname='Corn', age=32, groups=[]),
 User(firstname='Dave', lastname='Durian', age=33, groups=[]),
 User(firstname='Eve', lastname='Elderberry', age=34, groups=[]),
 User(firstname='Mallory', lastname='Melon', age=15, groups=[])]
"""

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`

# %% Imports
import json

# %% Types
from typing import Callable
decoder: Callable[[dict], object]
result: list[object]

# %% Data
DATA = (
    '[{"_clsname": "User", "firstname": "Alice", "lastname": "Apricot", "age": 30, "groups": []}, '
    '{"_clsname": "User", "firstname": "Bob", "lastname": "Blackthorn", "age": 31, "groups": []}, '
    '{"_clsname": "User", "firstname": "Carol", "lastname": "Corn", "age": 32, "groups": []}, '
    '{"_clsname": "User", "firstname": "Dave", "lastname": "Durian", "age": 33, "groups": []}, '
    '{"_clsname": "User", "firstname": "Eve", "lastname": "Elderberry", "age": 34, "groups": []}, '
    '{"_clsname": "User", "firstname": "Mallory", "lastname": "Melon", "age": 15, "groups": []}]'
)


class User:
    def __init__(self, firstname, lastname, age=None, groups=None):
        self.firstname = firstname
        self.lastname = lastname
        self.age = age
        self.groups = groups if groups else []

    def __repr__(self):
        clsname = self.__class__.__qualname__
        arguments = ', '.join(f'{k}={v!r}' for k,v in vars(self).items())
        return f'{clsname}({arguments})'


# %% Result
result = ...