14.4. Function Arguments

  • Argument - value/variable/reference being passed to the function

  • Positional argument - value passed to function - order is important

  • Keyword argument - value passed to function resolved by name - order is not important

Function definition with parameters:

myfunction(<arguments>)
>>> add(1, 2)  
>>> add(a=1, b=2)  
>>> add(1, b=2)  
argument

Value/variable/reference being passed to the function

positional argument

Value passed to function - order is important

keyword argument

Value passed to function resolved by name - order is not important

14.4.1. Positional Arguments

  • Order of positional arguments has significance

Let's define a function:

>>> def echo(a, b):
...     return f'{a=}, {b=}'

Positional arguments are resolved by order. This mean, that the first argument will be assigned to the first parameter, and the second argument to the second parameter and so on:

>>> echo(1, 2)
'a=1, b=2'

The order of positional parameters is important:

>>> echo(2, 1)
'a=2, b=1'

14.4.2. Keyword Arguments

  • Order of keyword arguments has no significance

Let's define a function:

>>> def echo(a, b):
...     return f'{a=}, {b=}'

Keyword arguments are resolved by name instead of the position. This mean, that the argument with particular name will be assigned to the corresponding parameter with the same name in function signature.

>>> echo(a=1, b=2)
'a=1, b=2'

The order of keyword parameters is not important, because values are assigned by name, not a position:

>>> echo(b=2, a=1)
'a=1, b=2'

14.4.3. Positional and Keyword Arguments

  • Positional arguments must be at the left side

  • Keyword arguments must be at the right side

>>> def echo(a, b):
...     return f'{a=}, {b=}'

All positional arguments must be on the left side, and all the required arguments must be on the right side:

>>> echo(1, b=2)
'a=1, b=2'

Passing positional argument which follows keyword argument will yield a SyntaxError:

>>> echo(a=1, 2)
Traceback (most recent call last):
SyntaxError: positional argument follows keyword argument

Positional argument are resolved first. Defining keyword argument which follows positional argument with the same name will yield a TypeError:

>>> echo(1, a=2)
Traceback (most recent call last):
TypeError: echo() got multiple values for argument 'a'

14.4.4. Errors

>>> def echo(a, b, c, d, e):
...     return f'{a=}, {b=}, {c=}, {d=}, {e=}'
>>>
>>>
>>> echo(1, 2, 3)
Traceback (most recent call last):
TypeError: echo() missing 2 required positional arguments: 'd' and 'e'
>>>
>>> echo(1, 2, 3, d=4)
Traceback (most recent call last):
TypeError: echo() missing 1 required positional argument: 'e'
>>>
>>> echo(1, 2, 3, d=4, 5)
Traceback (most recent call last):
SyntaxError: positional argument follows keyword argument
>>>
>>> echo(1, 2, 4, 5, c=3)
Traceback (most recent call last):
TypeError: echo() got multiple values for argument 'c'
>>>
>>> echo(1, 2, 3, d=4, e=5)
'a=1, b=2, c=3, d=4, e=5'

14.4.5. Use Case - 0x01

>>> def say_hello(text='say what?'):
...      return text
>>>
>>>
>>> say_hello('hello')
'hello'
>>>
>>> say_hello(text='hello world')
'hello world'
>>>
>>> say_hello()
'say what?'

14.4.6. Use Case - 0x02

>>> def connect(*args, **kwargs):
...     pass
>>> connect('myusername', 'mypassword')
>>> connect('myusername', 'mypassword', 'example.com', 443, False, 1, True)
>>> connect(host='example.com', username='myusername', password='mypassword')
>>> connect(
...     host='example.com',
...     username='myusername',
...     password='mypassword',
...     port=443,
...     ssl=True,
...     persistent=True)

14.4.7. Use Case - 0x03

>>> def read_csv(*args, **kwargs):
...     pass

Calling function with positional only arguments is insane. In Python we don't do that, because we have keyword arguments.

>>> read_csv('myfile.csv', ';', None, 'infer', None, None, None, False, None,
...          True, None, None, None, None, None, False, None, None, None,
...          True, True, False, True, False, False, False, None, False,
...          False, None, 'infer', None, b',', None, '"', 0, None, None,
...          None, None, None, True, True, 0, True, False, True, False, None)

Keyword arguments with sensible defaults are your best friends. The number of function parameters suddenly is not a problem:

>>> read_csv('myfile1.csv', delimiter=';', decimal=b',')
>>> read_csv('myfile2.csv', delimiter=';', decimal=b',')
>>> read_csv('myfile3.csv', delimiter=';', decimal=b',')
>>> read_csv('myfile4.csv', delimiter=';', decimal=b',')
>>> read_csv('myfile5.csv', delimiter=';', decimal=b',')
>>> read_csv('iris.csv')
>>> read_csv('iris.csv', encoding='utf-8')
>>> read_csv('iris.csv', encoding='utf-8', parse_dates=['birthdate'])
>>> read_csv('iris.csv', skiprows=3, delimiter=';')
>>> read_csv('iris.csv',
...     encoding='utf-8',
...     skiprows=3,
...     delimiter=';',
...     usecols=['sepal_length', 'species'],
...     parse_dates=['birthdate'])

14.4.8. Assignments

Code 14.14. Solution
# TODO: to zadanie bardziej pasuje do function_parameters
"""
* Assignment: Function Arguments Sequence
* Type: class assignment
* Complexity: easy
* Lines of code: 2 lines
* Time: 3 min

English:
    1. Define function `total`:
        a. parameter: list of integers (required)
        b. return: sum only even numbers
    2. Use `even()` to check if number is even
    3. Run doctests - all must succeed

Polish:
    1. Zdefiniuj funkcję `total`:
        a. parametr: lists liczb całkowitych (wymagany)
        b. zwraca: sumę tylko parzystych liczb
    2. Użyj `even()` do sprawdzenia czy liczba jest parzysta
    3. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isfunction

    >>> assert total is not Ellipsis, \
    'Write solution inside `total` function'
    >>> assert isfunction(total), \
    'Object `total` must be a function'

    >>> data = [1, 2, 3, 4]
    >>> total(data)
    6

    >>> data = [2, -1, 0, 2]
    >>> total(data)
    4

    >>> data = list(range(0,101))
    >>> total(data)
    2550
"""

def even(x):
    return x % 2 == 0


# Define function `total()`:
# - parameter: sequence of integers
# - return: sum only even numbers
# Use `even()` to check if number is even
# type: Callable[[list[int]], int]
def total():
    ...

Code 14.15. Solution
# TODO: to zadanie bardziej pasuje do function_parameters
"""
* Assignment: Function Arguments Divide
* Type: class assignment
* Complexity: easy
* Lines of code: 4 lines
* Time: 3 min

English:
    1. Define function `divide`:
        a. parameter `a: int` - first number (required)
        b. parameter `b: int` - second number (required)
        c. return result of division of both arguments
    2. If division cannot be made raise `ValueError`
       with message "Argument `b` cannot be zero"
    3. Run doctests - all must succeed

Polish:
    1. Zdefiniuj funkcję `divide`:
        a. parametr `a: int` - pierwsza liczba (wymagany)
        b. parametr `b: int` - druga liczba (wymagany)
        c. zwróć wynik dzielenia obu argumentów
    2. Jeżeli dzielenie nie może być wykonane podnieś `ValueError`
       z komunikatem "Argument `b` cannot be zero"
    3. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isfunction

    >>> assert divide is not Ellipsis, \
    'Write solution inside `divide` function'
    >>> assert isfunction(divide), \
    'Object `divide` must be a function'

    >>> divide(4, 0)
    Traceback (most recent call last):
    ValueError: Argument `b` cannot be zero

    >>> divide(4, 2)
    2.0
"""

# Define function `divide`:
# - parameter `a: int` - first number
# - parameter `b: int` - second number
# - return result of division of both arguments
# If division cannot be made raise `ValueError` with message "Argument `b` cannot be zero"
# type: Callable[[int, int], float]
def divide(a, b):
    ...


Code 14.16. Solution
# TODO: to zadanie bardziej pasuje do function_parameters
"""
* Assignment: Function Arguments Power
* Type: class assignment
* Complexity: easy
* Lines of code: 4 lines
* Time: 3 min

English:
    1. Define function `power`:
        a. parameter `a: int` - first number (required)
        b. parameter `b: int` - second number (optional)
        c. returns: power of the first argument to the second
    2. If only one argument was passed,
       consider second equal to the first one
    3. Run doctests - all must succeed

Polish:
    1. Zdefiniuj funkcję `power`:
        a. parametr `a: int` - pierwsza liczba (wymagany)
        b. parametr `b: int` - druga liczba (opcjonalny)
        c. zwraca: wynik pierwszego argumentu do potęgi drugiego
    2. Jeżeli tylko jeden argument był podany,
       przyjmij drugi równy pierwszemu
    6. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isfunction

    >>> assert power is not Ellipsis, \
    'Write solution inside `power` function'
    >>> assert isfunction(power), \
    'Object `power` must be a function'

    >>> power(4, 3)
    64
    >>> power(3)
    27
"""

# Define function `power`:
# - parameter `a: int` - first number (required)
# - parameter `b: int` - second number (optional)
# - returns: power of the first argument to the second
# If only one argument was passed, consider second equal to the first one
# type: Callable[[int, int], int]
def power():
    ...


Code 14.17. Solution
# TODO: to zadanie bardziej pasuje do function_parameters
"""
* Assignment: Function Arguments Translate
* Type: class assignment
* Complexity: easy
* Lines of code: 2 lines
* Time: 5 min

English:
    1. Define function `translate`:
        a. parameter `text: str` (required)
        b. return `str` with translated text
    2. If letter is in `PL` then substitute letter,
       otherwise take original letter
    3. Run doctests - all must succeed

Polish:
    1. Zdefiniuj funkcję `translate`:
        a. parametr `text: str` (wymagany)
        b. zwróć `str` z przetłumaczonym tekstem
    2. Jeżeli litera jest w `PL` to podmień literę,
        w przeciwnym przypadku to weź oryginalną literę
    3. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isfunction

    >>> assert translate is not Ellipsis, \
    'Write solution inside `translate` function'
    >>> assert isfunction(translate), \
    'Object `translate` must be a function'

    >>> translate('zażółć')
    'zazolc'
    >>> translate('gęślą')
    'gesla'
    >>> translate('jaźń')
    'jazn'
    >>> translate('zażółć gęślą jaźń')
    'zazolc gesla jazn'
"""

PL = {
    'ą': 'a',
    'ć': 'c',
    'ę': 'e',
    'ł': 'l',
    'ń': 'n',
    'ó': 'o',
    'ś': 's',
    'ż': 'z',
    'ź': 'z',
}

# Define function `translate`:
# - parameter `text: str` (required)
# - return `str` with translated text
# If letter is in `PL` then substitute letter, otherwise take original letter
# type: Callable[[str], str]
def translate():
    ...


Code 14.18. Solution
# TODO: to zadanie bardziej pasuje do function_parameters
# TODO: Translate input data to English
# TODO: zamieniać wiele spacji na jedną, a nie na pusty znak
"""
* Assignment: Function Arguments Clean
* Type: homework
* Complexity: medium
* Lines of code: 15 lines
* Time: 13 min

English:
    1. Define function `clean`:
        a. parameter `text: str` (required)
        b. returns `str` with cleaned text
    2. To clean text:
        a. Remove unwanted whitespaces
        b. Remove unwanted special characters
        c. Remove unwanted fragments
        d. Format text
    3. Run doctests - all must succeed

Polish:
    1. Zdefiniuj funkcję `clean`:
        a. parametr `text: str` (wymagany)
        b. zwraca `str` z oczyszczonym tekstem
    2. Aby oczyścić tekst:
        a. Usuń niechciane białe znaki
        b. Usuń niechciane znaki specjalne
        c. Usuń niechciane fragmenty
        d. Sformatuj tekst
    3. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isfunction

    >>> assert clean is not Ellipsis, \
    'Write solution inside `clean` function'
    >>> assert isfunction(clean), \
    'Object `clean` must be a function'

    >>> clean('ul.Mieszka II')
    'Mieszka II'
    >>> clean('UL. Zygmunta III WaZY')
    'Zygmunta III Wazy'
    >>> clean('  bolesława chrobrego ')
    'Bolesława Chrobrego'
    >>> clean('ul Jana III SobIESkiego')
    'Jana III Sobieskiego'
    >>> clean('\tul. Jana trzeciego Sobieskiego')
    'Jana III Sobieskiego'
    >>> clean('ulicaJana III Sobieskiego')
    'Jana III Sobieskiego'
    >>> clean('UL. JA    NA 3 SOBIES  KIEGO')
    'Jana III Sobieskiego'
    >>> clean('ULICA JANA III SOBIESKIEGO  ')
    'Jana III Sobieskiego'
    >>> clean('ULICA. JANA III SOBIeskieGO')
    'Jana III Sobieskiego'
    >>> clean(' Jana 3 Sobieskiego  ')
    'Jana III Sobieskiego'
    >>> clean('Jana III Sobi  eskiego ')
    'Jana III Sobieskiego'
"""


Code 14.19. Solution
"""
* Assignment: Function Arguments Num2Str
* Type: homework
* Complexity: medium
* Lines of code: 5 lines
* Time: 8 min

English:
    1. Given is pilot's alphabet for numbers
    2. Convert `DATA: dict[int, str]` to `data: dict[str, str]` (keys as `str`)
    3. Define function `pilot_say` converting `int` or `float`
       to text form in Pilot's Speak
    4. You cannot change `DATA`, but you can modify `data`
    5. Run doctests - all must succeed

Polish:
    1. Dany jest alfabet pilotów dla numerów
    2. Przekonwertuj `DATA: dict[int, str]` na `data: dict[str, str]`
       (klucze jako `str`)
    3. Zdefiniuj funkcję `pilot_say` konwertującą `int` lub `float`
       na formę tekstową w mowie pilotów
    4. Nie możesz zmieniać `DATA`, ale możesz modyfikować `data`
    5. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isfunction

    >>> assert pilot_say is not Ellipsis, \
    'Write solution inside `pilot_say` function'
    >>> assert isfunction(pilot_say), \
    'Object `pilot_say` must be a function'

    >>> pilot_say(1)
    'one'
    >>> pilot_say(+1)
    'one'
    >>> pilot_say(-1)
    'minus one'
    >>> pilot_say(1+1)
    'two'
    >>> pilot_say(1-1)
    'zero'
    >>> pilot_say(1969)
    'one niner six niner'
    >>> pilot_say(31337)
    'tree one tree tree seven'
    >>> pilot_say(13.37)
    'one tree and tree seven'
    >>> pilot_say(31.337)
    'tree one and tree tree seven'
    >>> pilot_say(-1969)
    'minus one niner six niner'
    >>> pilot_say(-31.337)
    'minus tree one and tree tree seven'
    >>> pilot_say(-49.35)
    'minus fower niner and tree fife'
    >>> pilot_say(1.0)
    'one and zero'
    >>> pilot_say(1.)
    'one and zero'
    >>> pilot_say(123.)
    'one two tree and zero'
    >>> pilot_say(123.0)
    'one two tree and zero'
    >>> pilot_say(.44)
    'zero and fower fower'
    >>> pilot_say(1-)
    Traceback (most recent call last):
    SyntaxError: invalid syntax
"""

DATA = {
    0: 'zero',
    1: 'one',
    2: 'two',
    3: 'tree',
    4: 'fower',
    5: 'fife',
    6: 'six',
    7: 'seven',
    8: 'ait',
    9: 'niner',
}

Code 14.20. Solution
"""
* Assignment: Function Arguments Range
* Type: homework
* Complexity: medium
* Lines of code: 7 lines
* Time: 13 min

English:
    1. Define function `myrange` with parameters: `start`, `stop`, `step`
    2. Write own implementation of a built-in function
       `myrange(start, stop, step)`
    3. Do not use built-in `range()` function
    4. Run doctests - all must succeed

Polish:
    1. Zdefiniuj funkcję `myrange` z parametrami: `start`, `stop`, `step`
    2. Zaimplementuj własne rozwiązanie wbudowanej funkcji
       `myrange(start, stop, step)`
    3. Nie używaj wbudowanej funkcji `range()`
    4. Uruchom doctesty - wszystkie muszą się powieść

Hints:
    * `while`

Tests:
    >>> import sys; sys.tracebacklimit = 0
    >>> from inspect import isfunction

    >>> assert myrange is not Ellipsis, \
    'Write solution inside `myrange` function'
    >>> assert isfunction(myrange), \
    'Object `myrange` must be a function'

    >>> myrange(0, 10, 2)
    [0, 2, 4, 6, 8]

    >>> myrange(0, 5)
    [0, 1, 2, 3, 4]
"""