• json.dumps(object) -> str - Python object to JSON string

  • json.dump(object) -> file - Python object to JSON file

  • file extension .json

15.2.1. SetUp

15.2.2. Sequence

>>> DATA = ('Alice', 'Apricot', 30)
>>>
>>> result = json.dumps(DATA)
>>>
>>> print(result)
["Alice", "Apricot", 30]

15.2.3. List of Sequences

>>> DATA = [
...     ('firstname', 'lastname', 'age'),
...     ('Alice', 'Apricot', 30),
...     ('Bob', 'Blackthorn', 31),
...     ('Carol', 'Corn', 32),
...     ('Dave', 'Durian', 33),
...     ('Eve', 'Elderberry', 34),
...     ('Mallory', 'Melon', 15),
... ]
>>>
>>> result = json.dumps(DATA)
>>>
>>> print(result)
[["firstname", "lastname", "age"],
 ["Alice", "Apricot", 30],
 ["Bob", "Blackthorn", 31],
 ["Carol", "Corn", 32],
 ["Dave", "Durian", 33],
 ["Eve", "Elderberry", 34],
 ["Mallory", "Melon", 15]]

15.2.4. Mapping

>>> DATA = {'firstname': 'Alice', 'lastname': 'Apricot', 'age': 30}
>>>
>>> result = json.dumps(DATA)
>>>
>>> print(result)
{"firstname": "Alice", "lastname": "Apricot", "age": 30}

15.2.5. List of Mappings

>>> DATA = [
...     {'firstname': 'Alice', 'lastname': 'Apricot', 'age': 30},
...     {'firstname': 'Bob', 'lastname': 'Blackthorn', 'age': 31},
...     {'firstname': 'Carol', 'lastname': 'Corn', 'age': 32},
...     {'firstname': 'Dave', 'lastname': 'Durian', 'age': 33},
...     {'firstname': 'Eve', 'lastname': 'Elderberry', 'age': 34},
...     {'firstname': 'Mallory', 'lastname': 'Melon', 'age': 15},
... ]
>>>
>>> result = json.dumps(DATA)
>>>
>>> print(result)
[{"firstname": "Alice", "lastname": "Apricot", "age": 30},
 {"firstname": "Bob", "lastname": "Blackthorn", "age": 31},
 {"firstname": "Carol", "lastname": "Corn", "age": 32},
 {"firstname": "Dave", "lastname": "Durian", "age": 33},
 {"firstname": "Eve", "lastname": "Elderberry", "age": 34},
 {"firstname": "Mallory", "lastname": "Melon", "age": 15}]

15.2.6. To File

  • json.dump(data, file) -> None

  • file extension .json

def dump(obj: Any,
         fp: IO[str],
         *,
         skipkeys: bool = ...,
         ensure_ascii: bool = ...,
         check_circular: bool = ...,
         allow_nan: bool = ...,
         cls: type[JSONEncoder] | None = ...,
         indent: None | int | str = ...,
         separators: tuple[str, str] | None = ...,
         default: (Any) -> Any | None = ...,
         sort_keys: bool = ...,
         **kwds: Any) -> None

SetUp:

>>> DATA = {'firstname': 'Alice', 'lastname': 'Apricot', 'age': 30}

Usage:

>>> with open('/tmp/myfile.json', mode='wt') as file:
...     json.dump(DATA, file)

Result:

>>> result = open('/tmp/myfile.json').read()
>>> print(result)
{"firstname": "Alice", "lastname": "Apricot", "age": 30}

15.2.7. Assignments

# %% About
# - Name: JSON Dump Sequence
# - Difficulty: easy
# - Lines: 1
# - Minutes: 1

# %% 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. Use `json` module
# 3. Result write to variable `result`
# 4. Run doctests - all must succeed

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

# %% Expected
# >>> result
# ["Alice", "Apricot", 30]

# %% Hints
# - `json.dumps()`

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

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

>>> assert 'result' in globals(), \
'Variable `result` is not defined; assign result of your program to it.'

>>> assert result is not Ellipsis, \
'Variable `result` has an invalid value; assign result of your program to it.'

>>> assert type(result) is str, \
'Variable `result` has an invalid type; expected: `str`.'

>>> assert len(result) > 0, \
'Variable `result` has an invalid length; expected more than zero elements.'

>>> print(result)
["Alice", "Apricot", 30]
"""

# %% 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
result: str

# %% Data
DATA = ('Alice', 'Apricot', 30)

# %% Result
result = ...


# %% About
# - Name: JSON Dump ListSequence
# - Difficulty: easy
# - Lines: 1
# - Minutes: 1

# %% 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. Use `json` module
# 3. Result write to variable `result`
# 4. Run doctests - all must succeed

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

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

# %% Hints
# - `json.dumps()`

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

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

>>> assert 'result' in globals(), \
'Variable `result` is not defined; assign result of your program to it.'

>>> assert result is not Ellipsis, \
'Variable `result` has an invalid value; assign result of your program to it.'

>>> assert type(result) is str, \
'Variable `result` has an invalid type; expected: `str`.'

>>> assert len(result) > 0, \
'Variable `result` has an invalid length; expected more than zero elements.'

>>> print(result)  # doctest: +NORMALIZE_WHITESPACE
[["firstname", "lastname", "age"],
 ["Alice", "Apricot", 30],
 ["Bob", "Blackthorn", 31],
 ["Carol", "Corn", 32],
 ["Dave", "Durian", 33],
 ["Eve", "Elderberry", 34],
 ["Mallory", "Melon", 15]]
"""

# %% 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
result: str

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

# %% Result
result = ...


# %% About
# - Name: JSON Dump Mapping
# - Difficulty: easy
# - Lines: 1
# - Minutes: 1

# %% 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. Use `json` module
# 3. Result write to variable `result`
# 4. Run doctests - all must succeed

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

# %% Expected
# >>> result
# {"firstname": "Alice", "lastname": "Apricot", "age": 30}

# %% Hints
# - `json.dumps()`

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

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

>>> assert 'result' in globals(), \
'Variable `result` is not defined; assign result of your program to it.'

>>> assert result is not Ellipsis, \
'Variable `result` has an invalid value; assign result of your program to it.'

>>> assert type(result) is str, \
'Variable `result` has an invalid type; expected: `str`.'

>>> assert len(result) > 0, \
'Variable `result` has an invalid length; expected more than zero elements.'

>>> print(result)
{"firstname": "Alice", "lastname": "Apricot", "age": 30}
"""

# %% 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
result: str

# %% Data
DATA = {'firstname': 'Alice', 'lastname': 'Apricot', 'age': 30}

# %% Result
result = ...


# %% About
# - Name: JSON Dump ListMapping
# - Difficulty: easy
# - Lines: 1
# - Minutes: 1

# %% 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. Use `json` module
# 3. Result write to variable `result`
# 4. Run doctests - all must succeed

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

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

# %% Hints
# - `json.dumps()`

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

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

>>> assert 'result' in globals(), \
'Variable `result` is not defined; assign result of your program to it.'

>>> assert result is not Ellipsis, \
'Variable `result` has an invalid value; assign result of your program to it.'

>>> assert type(result) is str, \
'Variable `result` has an invalid type; expected: `str`.'

>>> assert len(result) > 0, \
'Variable `result` has an invalid length; expected more than zero elements.'

>>> print(result)  # doctest: +NORMALIZE_WHITESPACE
[{"firstname": "Alice", "lastname": "Apricot", "age": 30},
 {"firstname": "Bob", "lastname": "Blackthorn", "age": 31},
 {"firstname": "Carol", "lastname": "Corn", "age": 32},
 {"firstname": "Dave", "lastname": "Durian", "age": 33},
 {"firstname": "Eve", "lastname": "Elderberry", "age": 34},
 {"firstname": "Mallory", "lastname": "Melon", "age": 15}]
"""

# %% 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
result: str

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

# %% Result
result = ...


# %% About
# - Name: JSON Dump ToFile
# - Difficulty: easy
# - Lines: 2
# - Minutes: 2

# %% 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. Use `json` module
# 3. Result write to file `FILE`
# 4. Run doctests - all must succeed

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

# %% Hints
# - `with open(mode='wt') as file:`
# - `json.dump()`

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

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

>>> from os import remove
>>> result = open(FILE).read()
>>> remove(FILE)

>>> assert 'result' in globals(), \
'Variable `result` is not defined; assign result of your program to it.'

>>> assert result is not Ellipsis, \
'Variable `result` has an invalid value; assign result of your program to it.'

>>> assert type(result) is str, \
'Variable `result` has an invalid type; expected: `str`.'

>>> assert len(result) > 0, \
'Variable `result` has an invalid length; expected more than zero elements.'

>>> print(result)  # doctest: +NORMALIZE_WHITESPACE
[{"firstname": "Alice", "lastname": "Apricot", "age": 30},
 {"firstname": "Bob", "lastname": "Blackthorn", "age": 31},
 {"firstname": "Carol", "lastname": "Corn", "age": 32},
 {"firstname": "Dave", "lastname": "Durian", "age": 33},
 {"firstname": "Eve", "lastname": "Elderberry", "age": 34},
 {"firstname": "Mallory", "lastname": "Melon", "age": 15}]
"""

# %% 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

# %% Data
FILE = '_temporary.json'

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

# %% Result