13.5. Pickle Objects

13.5.1. Assignments

# %% About
# - Name: Pickle Recap ListObjects
# - 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. Define `result: list[object]` with deserialized data from `FILE`
# 2. Use `pickle` module
# 3. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result: list[object]` z zdeserializowanymi danymi z `FILE`
# 2. Użyj modułu `pickle`
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Example
# >>> result
# [User(firstname='Alice', lastname='Apricot', age=30, email=None, groups=[users, staff]),
#  User(firstname='Bob', lastname='Blackthorn', age=31, email=None, groups=[users, staff]),
#  User(firstname='Carol', lastname='Corn', age=32, email=None, groups=[users]),
#  User(firstname='Dave', lastname='Durian', age=33, email=None, groups=[users]),
#  User(firstname='Eve', lastname='Elderberry', age=34, email=None, groups=[users, staff, admins]),
#  User(firstname='Mallory', lastname='Melon', age=15, email=None, groups=[])]

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> from os import remove
>>> remove(FILE)

>>> assert type(result) is list, \
'Variable `result` has invalid type, should be list'

>>> assert all(type(row) is User for row in result), \
'Variable `result` has invalid type, should be User'

>>> from pprint import pprint
>>> pprint(result, width=79, sort_dicts=False)
[User(firstname='Alice', lastname='Apricot', age=30, email=None, groups=[users, staff]),
 User(firstname='Bob', lastname='Blackthorn', age=31, email=None, groups=[users, staff]),
 User(firstname='Carol', lastname='Corn', age=32, email=None, groups=[users]),
 User(firstname='Dave', lastname='Durian', age=33, email=None, groups=[users]),
 User(firstname='Eve', lastname='Elderberry', age=34, email=None, groups=[users, staff, admins]),
 User(firstname='Mallory', lastname='Melon', age=15, email=None, 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 pickle

# %% Types
result: list[object]

# %% Data
FILE = r'_temporary.pkl'

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

with open(FILE, mode='wb') as file:
    pickle.dump(DATA, file)

# %% Result