15.3. Function Parameters

• Parameter - What you specify while defining a function

• Required parameter - necessary to call that function

• Required parameter - specified at leftmost side

• Default parameter - optional to call that function

• Default parameter - Has default value

• Default parameter - Could be overridden

• Default parameter - Specified at rightmost side

parameter

Receiving variable used within the function/block

required parameter

Parameter which is necessary to call function

default parameter

Parameter which is optional and has default value (if not specified at call time)

signature

Function name and its parameters

Syntax:

def myfunction(<parameters>):
    pass

Example:

>>> def login(username, password):
...     pass

15.3.1. Required Parameters

• Parameters without default values are required

>>> def login(username, password):
...     pass

15.3.2. Default Parameters

• Default parameters has default value

• Function will use default value if not overwritten by user

• Parameters with default values can be omitted while executing

>>> def login(username=None, password=None):
...     pass

15.3.3. Required and Default Parameters

• Required parameters must be at the left side

• Default parameters must be at the right side

• There cannot be required parameter after optional

>>> def login(username, password=None):
...     pass

15.3.4. Errors

>>> def login(username=None, password):
...     pass
Traceback (most recent call last):
SyntaxError: parameter without a default follows parameter with a default

15.3.5. Help

• Signature - Name and parameters of a function

>>> def login(username, password=None):
...     pass
>>>
>>> help(login)
Help on function login in module __main__:

login(username, password=None)

15.3.6. Recap

• Parameter - What you specify while defining a function

• Required parameter - necessary to call that function

• Required parameter - specified at leftmost side

• Default parameter - optional to call that function

• Default parameter - Has default value

• Default parameter - Could be overridden

• Default parameter - Specified at rightmost side

>>> def login(username, password=None):
...     pass

• Function is called login.

• It has two parameters - username and password.

• username is a required parameter.

• password is a default parameter with default value of None.

15.3.7. Use Case - 1

>>> def echo(text):
...     return text

15.3.8. Use Case - 2

>>> def age_category(age):
...     if age < 18:
...         return 'junior'
...     else:
...         return 'senior'

>>> age_category(10)
'junior'

>>> age_category(41)
'senior'

15.3.9. Use Case - 3

>>> def connect(username, password, host='127.0.0.1', port=22,
...             ssl=True, keep_alive=1, persistent=False): ...

15.3.10. Use Case - 4

• Source: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.read_csv.html

Definition of pandas.read_csv() function:

>>> def read_csv(filepath_or_buffer, sep=', ', delimiter=None, header='infer',
...              names=None, index_col=None, usecols=None, squeeze=False,
...              prefix=None, mangle_dupe_cols=True, dtype=None, engine=None,
...              converters=None, true_values=None, false_values=None,
...              skipinitialspace=False, skiprows=None, nrows=None,
...              na_values=None, keep_default_na=True, na_filter=True,
...              verbose=False, skip_blank_lines=True, parse_dates=False,
...              infer_datetime_format=False, keep_date_col=False,
...              date_parser=None, dayfirst=False, iterator=False,
...              chunksize=None, compression='infer', thousands=None,
...              decimal=b'.', lineterminator=None, quotechar='"',
...              quoting=0, escapechar=None, comment=None, encoding=None,
...              dialect=None, tupleize_cols=None, error_bad_lines=True,
...              warn_bad_lines=True, skipfooter=0, doublequote=True,
...              delim_whitespace=False, low_memory=True, memory_map=False,
...              float_precision=None): ...

15.3.11. Assignments

# %% About
# - Name: Function Parameters Square
# - 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 function `square`:
#    - takes `x`
#    - returns `x` squared
# 2. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj funkcję `square`:
#    - przyjmuje `x`
#    - zwraca `x` do kwadratu
# 2. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> square(8)
# 64

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> from inspect import isfunction

>>> assert square is not Ellipsis, \
'Variable `square` has an invalid value; assign result of your program to it.'

>>> assert isfunction(square), \
'Object `square` must be a function'

>>> square(2)
4

>>> square(8)
64

>>> square(32)
1024
"""

# %% 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

# %% Types
from typing import Callable
square: Callable[[int], int]

# %% Data

# %% Result

# %% About
# - Name: Function Parameters IsEven
# - 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 function `is_even`:
#    - takes `x`
#    - returns True/False if `x` is even
# 2. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj funkcję `is_even`:
#    - przyjmuje `x`
#    - zwraca True/False czy `x` jest parzysty
# 2. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> is_even(1)
# False
#
# >>> is_even(2)
# True

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> from inspect import isfunction

>>> assert is_even is not Ellipsis, \
'Variable `is_even` has an invalid value; assign result of your program to it.'

>>> assert isfunction(is_even), \
'Object `is_even` must be a function'

>>> is_even(2)
True

>>> is_even(3)
False

>>> is_even(4)
True

>>> is_even(5)
False

>>> is_even(6)
True

>>> is_even(7)
False
"""

# %% 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

# %% Types
from typing import Callable
is_even: Callable[[int], bool]

# %% Data

# %% Result

# %% About
# - Name: Function Parameters Sum
# - 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 function `mysum`:
#    - takes `data`
#    - returns sum of all values in a list
# 2. Do not use built-in `sum()` function
# 3. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj funkcję `mysum`:
#    - przyjmuje `data`
#    - zwraca sumę wszystkich wartości z listy
# 2. Nie używaj wbudowanej funkcji `sum`
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> mysum([1, 2, 3])
# 6

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> from inspect import isfunction

>>> assert mysum is not Ellipsis, \
'Variable `mysum` has an invalid value; assign result of your program to it.'

>>> assert isfunction(mysum), \
'Object `mysum` must be a function'

>>> mysum([1, 2, 3])
6

>>> mysum([1, 2, 3, 4, 5, 6])
21
"""

# %% 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

# %% Types
from typing import Callable
mysum: Callable[[tuple|list|set], int|float]

# %% Data

# %% Result

# %% About
# - Name: Function Parameters mylocals
# - 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 function `mylocals` with two parameters
# 2. Parameter `firstname` is required
# 3. Parameter `lastname` is required
# 4. Return `firstname` and `lastname` as a `dict`,
#    example: {'firstname': 'Alice', 'lastname': 'Apricot'}
# 5. Do not use built-in function `locals()`
# 6. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj funkcję `mylocals` z dwoma parametrami
# 2. Parametr `firstname` jest wymagany
# 3. Parametr `lastname` jest wymagany
# 4. Zwróć `firstname` i `lastname` jako `dict`,
#    przykład: {'firstname': 'Alice', 'lastname': 'Apricot'}
# 5. Nie używaj wbudowanej funkcji `locals()`
# 6. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> mylocals('Alice', 'Apricot')
# {'firstname': 'Alice', 'lastname': 'Apricot'}

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> from inspect import isfunction

>>> assert mylocals is not Ellipsis, \
'Variable `mylocals` has an invalid value; assign result of your program to it.'

>>> assert isfunction(mylocals), \
'Object `mylocals` must be a function'

>>> mylocals('Alice', 'Apricot')
{'firstname': 'Alice', 'lastname': 'Apricot'}

>>> mylocals('Bob', 'Blackthorn')
{'firstname': 'Bob', 'lastname': 'Blackthorn'}
"""

# %% 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

# %% Types
from typing import Callable
mylocals: Callable[[int, int], dict[str, int]]

# %% Data

# %% Result

# %% About
# - Name: Function Parameters Default
# - Difficulty: easy
# - Lines: 4
# - 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 function `mypow` with two parameters
# 2. Parameter `base` is required
# 3. Parameter `exp` is optional and has default value `2`
# 4. Return `base` raised to the power of `exp`
# 5. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj funkcję `mypow` z dwoma parametrami
# 2. Parametr `base` jest wymagany
# 3. Parametr `exp` jest opcjonalny i ma domyślną wartością `2`
# 4. Zwróć `base` podniesione do potęgi `exp`
# 5. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> mypow(2)
# 4
#
# >>> mypow(base=2)
# 4
#
# >>> mypow(2, 10)
# 1024
#
# >>> mypow(base=2, exp=10)
# 1024

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> from inspect import isfunction

>>> assert mypow is not Ellipsis, \
'Variable `mypow` has an invalid value; assign result of your program to it.'

>>> assert isfunction(mypow), \
'Object `mypow` must be a function'

>>> mypow(2)
4

>>> mypow(base=2)
4

>>> mypow(2, 10)
1024

>>> mypow(base=2, exp=10)
1024
"""

# %% 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

# %% Types
from typing import Callable
mypow: Callable[[int, int|None], int]

# %% Data

# %% Result