16.11. OOP Method Parameters

  • Methods are functions in the class

  • Prevents copy-paste code

  • Improves readability

  • Improves refactoring

  • Decomposes bigger problem into smaller chunks

  • At definition - self should always be a first parameter

  • At call - self is not passed as an argument (Python will do that)

  • Later you will learn more advanced things like static methods etc.

Required parameter:

  • Necessary to call that function

  • Specified at leftmost side

Optional parameter:

  • Has default value

  • Optional to call that function

  • Default value will be overridden if specified at a call time

  • Specified at rightmost side

method

Functions in the class which takes instance as first argument (self)

16.11.1. Without Parameters

>>> class User:
...     def login(self):
...         print(f'User logged-in')

16.11.2. Required Parameters

  • At definition - self should always be a first parameter

  • Later you will learn more advanced things like static methods etc.

  • Parameter - Receiving variable used within the function

  • Parameters could be required or optional (with default value)

>>> class User:
...     def login(self, username, password):
...         print(f'User logged-in')

16.11.3. Optional Parameters

>>> class User:
...     def login(self, username=None, password=None):
...         print(f'User logged-in')

16.11.4. Required and Optional Parameters

>>> class User:
...     def login(self, username, password=None):
...         print(f'User logged-in')

16.11.5. Use Case - 0x01

>>> class User:
...     def login(self, username, password):
...         if username == 'mwatney' and password == 'nasa':
...             print('ok')
...         else:
...             raise PermissionError
...
>>>
>>>
>>> mark = User()
>>>
>>> mark.login()
Traceback (most recent call last):
TypeError: User.login() missing 2 required positional arguments: 'username' and 'password'
>>>
>>> mark.login('invalid', 'invalid')
Traceback (most recent call last):
PermissionError
>>>
>>> mark.login('mwatney', 'invalid')
Traceback (most recent call last):
PermissionError
>>>
>>> mark.login('invalid', 'nasa')
Traceback (most recent call last):
PermissionError
>>>
>>> mark.login('mwatney', 'nasa')
ok
>>>
>>> mark.login(username='mwatney', password='nasa')
ok

16.11.6. Assignments

Code 16.14. Solution
"""
* Assignment: OOP Method Syntax
* Type: class assignment
* Complexity: easy
* Lines of code: 3 lines
* Time: 3 min

English:
    1. Define class `Calculator`
    2. Define method `add` in class `Calculator`
    3. Method `add` take `a` and `b` as arguments
    4. Method returns sum of `a` and `b`
    5. Run doctests - all must succeed

Polish:
    1. Zdefiniuj klasę `Calculator`
    2. Zdefiniuj metodę `add` w klasie `Calculator`
    3. Metoda `add` przyjmuje `a` i `b` jako argumenty
    4. Metoda zwraca sumę `a` i `b`
    5. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isclass, ismethod

    >>> assert isclass(Calculator)
    >>> calc = Calculator()
    >>> assert ismethod(calc.add)
    >>> calc.add(1, 2)
    3
"""
Code 16.15. Solution
"""
* Assignment: OOP Method Mean
* Type: class assignment
* Complexity: easy
* Lines of code: 4 lines
* Time: 5 min

English:
    1. Define class `Stats`
    2. Define method `mean()` in `Stats` class
    3. Method takes `data: list[float]` as an argument
    4. Method returns arithmetic mean of the `data`
    5. Returned value must be rounded to one decimal places
    6. Run doctests - all must succeed

Polish:
    1. Zdefiniuj klasę `Stats`
    2. Zdefiniuj metodę `mean()` w klasie `Stats`
    3. Metoda przyjmuje `data: list[float]` jako argument
    4. Metoda zwraca średnią arytmetyczną z `data`
    5. Zwracana wartość ma być zaokrąglona do jednego miejsca po przecinku
    6. Uruchom doctesty - wszystkie muszą się powieść

Hints:
    * `round()`

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isclass, ismethod

    >>> assert isclass(Stats)
    >>> stats = Stats()
    >>> assert ismethod(stats.mean)

    >>> stats.mean([1, 2])
    1.5
    >>> stats.mean([5.8, 2.7, 5.1, 1.9])
    3.9
"""
Code 16.16. Solution
"""
* Assignment: OOP Method Call
* Type: class assignment
* Complexity: easy
* Lines of code: 1 lines
* Time: 3 min

English:
    1. Iterate over `DATA` skipping header and separating features from labels
    2. Call `mean()` method of `Stats` class instance passing list of features
    3. Define `result: list[float]` with list of means from each row
    4. Run doctests - all must succeed

Polish:
    1. Iteruj po `DATA` pomijając nagłówek i rodzielając cechy od etykiet
    2. Wywołuj metodę `mean()` instancji klasy `Stats` przekazując listę cech
    3. Zdefiniuj `result: list[float]` z listą średnich każdego z wierszy
    4. Uruchom doctesty - wszystkie muszą się powieść

Hints:
    * `round()`

Tests:
    >>> import sys; sys.tracebacklimit = 0

    >>> assert type(result) is list
    >>> assert all(type(x) is float for x in result)

    >>> result
    [3.9, 2.5, 3.5, 4.1, 3.9, 2.4]
"""

DATA = [
    ('sepal_length', 'sepal_width', 'petal_length', 'petal_width', 'species'),
    (5.8, 2.7, 5.1, 1.9, 'virginica'),
    (5.1, 3.5, 1.4, 0.2, 'setosa'),
    (5.7, 2.8, 4.1, 1.3, 'versicolor'),
    (6.3, 2.9, 5.6, 1.8, 'virginica'),
    (6.4, 3.2, 4.5, 1.5, 'versicolor'),
    (4.7, 3.2, 1.3, 0.2, 'setosa'),
]


class Stats:
    def mean(self, data):
        avg = sum(data) / len(data)
        return round(avg, 1)


stats = Stats()

# Apply `mean()` to each feature
# type: list[float]
result = ...