10.5. Pickle File

• File extension pkl

• rb reading in binary mode

• wb writing in binary mode

10.5.1. SetUp

>>> import pickle

10.5.2. Serialize to File

>>> DATA = [1, 2, 3]
>>>
>>> with open('/tmp/myfile.pkl', mode='wb') as file:
...     pickle.dump(DATA, file)

10.5.3. Deserialize from File

Load from file:

>>> with open('/tmp/myfile.pkl', mode='rb') as file:
...     result = pickle.load(file)
>>>
>>> print(result)
[1, 2, 3]

10.5.4. Assignments

Code 10.8. Solution

"""
* Assignment: Pickle File Serialize
* Complexity: easy
* Lines of code: 2 lines
* Time: 3 min

English:
    1. Save `DATA` to `FILE`
    2. Use `pickle` module
    3. Run doctests - all must succeed

Polish:
    1. Zapisz `DATA` do `FILE`
    2. Użyj modułu `pickle`
    3. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from os import remove

    >>> with open(FILE, mode='rb') as file:
    ...     result = pickle.load(file)

    >>> result  # doctest: +NORMALIZE_WHITESPACE
    [User(firstname='Mark', lastname='Watney', groups=[Group(gid=1, name='users')]),
     User(firstname='Melissa', lastname='Lewis', groups=[Group(gid=1, name='users'), Group(gid=2, name='admins')]),
     User(firstname='Rick', lastname='Martinez', groups=[])]

    >>> remove(FILE)
"""

import pickle
from dataclasses import dataclass, field

FILE = r'_temporary.pkl'

@dataclass
class Group:
    gid: int
    name: str


@dataclass
class User:
    firstname: str
    lastname: str
    groups: list[Group] | None


DATA = [
    User('Mark', 'Watney', groups=[
        Group(gid=1, name='users')]),
    User('Melissa', 'Lewis', groups=[
        Group(gid=1, name='users'),
        Group(gid=2, name='admins')]),
    User('Rick', 'Martinez', groups=[]),
]

Code 10.9. Solution

"""
* Assignment: Pickle File Deserialize
* Complexity: easy
* Lines of code: 2 lines
* Time: 3 min

English:
    1. Define `result: list[User]` with data from `FILE`
    2. Use `pickle` module
    3. Run doctests - all must succeed

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

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from os import remove

    >>> result  # doctest: +NORMALIZE_WHITESPACE
    [User(firstname='Mark', lastname='Watney', groups=[Group(gid=1, name='users')]),
     User(firstname='Melissa', lastname='Lewis', groups=[Group(gid=1, name='users'), Group(gid=2, name='admins')]),
     User(firstname='Rick', lastname='Martinez', groups=[])]

    >>> remove(FILE)
"""

import pickle
from dataclasses import dataclass, field

FILE = r'_temporary.pkl'
DATA = (
    b'\x80\x04\x95\xf9\x00\x00\x00\x00\x00\x00\x00]\x94(\x8c\rpickle_file_a'
    b'\x94\x8c\x04User\x94\x93\x94)\x81\x94}\x94(\x8c\tfirstname\x94\x8c\x04'
    b'Mark\x94\x8c\x08lastname\x94\x8c\x06Watney\x94\x8c\x06groups\x94]\x94h'
    b'\x01\x8c\x05Group\x94\x93\x94)\x81\x94}\x94(\x8c\x03gid\x94K\x01\x8c'
    b'\x04name\x94\x8c\x05users\x94ubaubh\x03)\x81\x94}\x94(h\x06\x8c\x07'
    b'Melissa\x94h\x08\x8c\x05Lewis\x94h\n]\x94(h\r)\x81\x94}\x94(h\x10K'
    b'\x01h\x11h\x12ubh\r)\x81\x94}\x94(h\x10K\x02h\x11\x8c\x06admins\x94'
    b'ubeubh\x03)\x81\x94}\x94(h\x06\x8c\x04Rick\x94h\x08\x8c\x08Martinez'
    b'\x94h\n]\x94ube.'
)

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


@dataclass
class Group:
    gid: int
    name: str


@dataclass
class User:
    firstname: str
    lastname: str
    groups: list[Group] | None