16.3. OOP Instance

• Definition: instance - object created from class

• Instances are objects

• Convention: snake_case names

• Convention: Two newlines between class and instances

instance

object

Computer software entity created from a class.

Figure 16.1. Class. Source: [1]

Figure 16.2. Instances. Source: [2]

16.3.1. One Class, One Instance

One class and one instance:

>>> class User:
...     pass
>>>
>>>
>>> mark = User()

16.3.2. One Class, Many Instances

One class and three instances:

>>> class User:
...     pass
>>>
>>>
>>> mark = User()
>>> melissa = User()
>>> rick = User()

16.3.3. Many Classes, Many Instances

Two classes and six instances. One instance of an Admin class, and five instances of User class:

>>> class User:
...     pass
...
>>> class Admin:
...     pass
>>>
>>>
>>> melissa = Admin()
>>> mark = User()
>>> rick = User()
>>> alex = User()
>>> beth = User()
>>> chris = User()

16.3.4. Naming

>>> class User:
...     pass
>>>
>>>
>>> mark = User()
>>> markwatney = User()
>>> mark_watney = User()

16.3.5. Type

• Builtin type() returns type (class) of an object

• type(obj)

• type(obj) is cls

>>> class User:
...     pass
>>>
>>> class Admin:
...     pass
>>>
>>>
>>> mark = User()
>>>
>>> type(mark)
<class '__main__.User'>
>>>
>>> type(mark) is User
True
>>>
>>> type(mark) is Admin
False

16.3.6. Isinstance

• isinstance() - returns if object is instance of class

• isinstance(mark, User)

• isinstance(mark, Admin)

• isinstance(mark, User|Admin)

>>> class User:
...     pass
>>>
>>> class Admin:
...     pass
>>>
>>>
>>> mark = User()
>>>
>>> isinstance(mark, User)
True
>>>
>>> isinstance(mark, Admin)
False
>>>
>>> isinstance(mark, User|Admin)
True

16.3.7. Instances of Builtin Classes

>>> a = int()
>>> b = float()
>>> c = bool()
>>> d = str()
>>> e = list()
>>> f = tuple()
>>> g = set()
>>> h = dict()

16.3.8. Use Case - 1

>>> x = list()
>>> y = list()

The above works because someone created class list():

>>> class List:
...     pass
>>>
>>>
>>> x = List()
>>> y = List()

16.3.9. Use Case - 2

>>> x = list()
>>> y = tuple()

The above works because someone created classes list() and tuple():

>>> class List:
...     pass
>>>
>>>
>>> class Tuple:
...     pass
>>>
>>>
>>> x = List()
>>> y = Tuple()

16.3.10. Use Case - 4

>>> class Astronaut:
...     pass
>>>
>>>
>>> mark = Astronaut()
>>> melissa = Astronaut()
>>> rick = Astronaut()
>>> alex = Astronaut()
>>> beth = Astronaut()
>>> chris = Astronaut()

16.3.11. Use Case - 5

>>> class AstronautPilot:
...     pass
...
>>> class AstronautScientist:
...     pass
...
>>> class AstronautEngineer:
...     pass
...
>>> class AstronautPhysician:
...     pass
>>>
>>>
>>> mark_watney = AstronautScientist()
>>> melissa_lewis = AstronautEngineer()
>>> rick_martinez = AstronautPilot()
>>> alex_vogel = AstronautScientist()
>>> beth_johanssen = AstronautEngineer()
>>> chris_beck = AstronautPhysician()

16.3.12. References

[1]

http://makieta.pl/12344-thickbox_default/faller-130803-blok-z-wielkiej-plyty-skala-h0.jpg

[2]

https://upload.wikimedia.org/wikipedia/commons/thumb/8/85/Os_Rusa_Poznań_RB1.jpg/1200px-Os_Rusa_Poznań_RB1.jpg

16.3.13. Assignments

# %% 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

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

# %% About
# - Name: OOP Instance One
# - Difficulty: easy
# - Lines: 1
# - Minutes: 2

# %% English
# 1. Create instance `mark` of a class `User`
# 1. Run doctests - all must succeed

# %% Polish
# 1. Stwórz instancję `mark` klasy `User`
# 1. Uruchom doctesty - wszystkie muszą się powieść

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

>>> from inspect import isclass

>>> assert isclass(User)
>>> assert isinstance(mark, User)
"""

class User:
    pass


# Create instance `mark` of a class `User`
# type: User
...

# %% 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

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

# %% About
# - Name: OOP Instance Many
# - Difficulty: easy
# - Lines: 3
# - Minutes: 2

# %% English
# 1. Create instance `mark` of a class `User`
# 2. Create instance `melissa` of a class `Admin`
# 3. Run doctests - all must succeed

# %% Polish
# 1. Stwórz instancję `mark` klasy `User`
# 2. Stwórz instancję `melissa` klasy `Admin`
# 3. Uruchom doctesty - wszystkie muszą się powieść

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

>>> from inspect import isclass

>>> assert isclass(User)
>>> assert isclass(Admin)

>>> assert isinstance(mark, User)
>>> assert isinstance(melissa, Admin)
"""

class User:
    pass

class Admin:
    pass


# Create instance `mark` of a class `User`
# type: User
...

# Create instance `melissa` of a class `Admin`
# type: Admin
...

# %% 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

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

# %% About
# - Name: OOP Instance IsInstance
# - Difficulty: easy
# - Lines: 3
# - Minutes: 2

# %% English
# 1. Define `result: type` with a result of checking a type of `mark`
# 2. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result: type` z wynikiem sprawdzania typu `marka`
# 2. Uruchom doctesty - wszystkie muszą się powieść

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

>>> from inspect import isclass
>>> assert isclass(User)

>>> assert result is not Ellipsis, \
'Assign your result to variable `result`'
>>> assert type(result) is type, \
'Variable `result` has invalid type, should be type'

>>> print(result)  # doctest: +ELLIPSIS
<class '....User'>
"""

class User:
    pass


mark = User()

# Define `result: type` with a result of checking a type of `mark`
# type: type[User]
result = ...

# %% 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

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

# %% About
# - Name: OOP Instance IsInstance
# - Difficulty: easy
# - Lines: 3
# - Minutes: 2

# %% English
# 1. Define `result: bool` with a result of checking
#    if `mark` is and instance of a class `User`
# 2. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result: bool` z wynikiem sprawdzania,
#    czy `mark` jest instancją klasy `User`
# 2. Uruchom doctesty - wszystkie muszą się powieść

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

>>> from inspect import isclass
>>> assert isclass(User)

>>> assert result is not Ellipsis, \
'Assign your result to variable `result`'
>>> assert type(result) is bool, \
'Variable `result` has invalid type, should be bool'

>>> print(result)
True
"""

class User:
    pass


mark = User()

# Define `result: bool` with a result of checking
# if `mark` is and instance of a class `User`
# type: bool
result = ...

# %% 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

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

# %% About
# - Name: OOP Instance IsInstance
# - Difficulty: easy
# - Lines: 3
# - Minutes: 2

# %% English
# 1. Define `result: bool` with a result of checking
#    if `mark` is and instance of a class `User` or `Admin`
# 2. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result: bool` z wynikiem sprawdzania,
#    czy `mark` jest instancją klasy `User` lub `Admin`
# 2. Uruchom doctesty - wszystkie muszą się powieść

# %% Tests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 10), \
'Python 3.10+ required'

>>> from inspect import isclass
>>> assert isclass(User)
>>> assert isclass(Admin)

>>> assert result is not Ellipsis, \
'Assign your result to variable `result`'
>>> assert type(result) is bool, \
'Variable `result` has invalid type, should be bool'

>>> print(result)
True
"""

class User:
    pass

class Admin:
    pass


mark = User()

# Define `result: bool` with a result of checking
# if `mark` is and instance of a class `User` or `Admin`
# type: bool
result = ...