8.3. Function Parameters¶

8.3.1. Rationale¶

parameter: Receiving variable used within the function/block
default parameter: Parameter which is optional and has default value (if not specified at call time)
required parameter: Parameter which is necessary to call function

8.3.2. Syntax¶

Listing 8.7. Function definition with parameters¶

def my_function(<parameters>):
    <do something>

def add(a, b):
    print(a + b)

8.3.3. Required Parameters¶

Parameters without default values are required

def add(a, b):
    print(a + b)


add()
# TypeError: add() missing 2 required positional arguments: 'a' and 'b'

add(1)
# TypeError: add() missing 1 required positional argument: 'b'

add(1, 2)
# 3

add(1, 2, 3)
# TypeError: add() takes 2 positional arguments but 3 were given

8.3.4. 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 add(a=10, b=20):
    print(a + b)


add()
# 30

add(1)
# 21

add(1, 2)
# 3

add(1, 2, 3)
# TypeError: add() takes from 0 to 2 positional arguments but 3 were given

8.3.5. 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 add(a, b=20):
    print(a + b)


add()
# TypeError: add() missing 1 required positional argument: 'a'

add(1)
# 21

add(1, 2)
# 3

add(1, 2, 3)
# TypeError: add() takes from 1 to 2 positional arguments but 3 were given

def add(a=1, b):
    print(a + b)

# SyntaxError: non-default argument follows default argument

def add(a, b=1, c):
    print(a + b + c)

# SyntaxError: non-default argument follows default argument

8.3.6. Examples¶

Listing 8.8. Example 1¶

def add(a, b):
    print(a + b)


add(1, 2)
# 3

add(1.5, 2.5)
# 4.0

add('a', 'b')
# 'ab'

Listing 8.9. Example 2¶

def echo(text):
    print(text)


echo('hello')
# hello

Listing 8.10. Example 3¶

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

    print('Connecting...')

Listing 8.11. Example 4. Definition of pandas.read_csv() function. Source: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.read_csv.html¶

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):

    print('Reading CSV...')

8.3.7. Assignments¶

8.3.7.1. Function Parameters Sequence¶

Complexity level: easy
Lines of code to write: 2 lines
Estimated time of completion: 3 min
Solution: solution/function_parameters_sequence.py

English

Define function add
Function parameter is sequence of integers
Print sum of all sequence values

Polish

Zdefiniuj funkcję add
Parametrem do funkcji ma być sekwencja liczb całkowitych
Wypisz sumę wszystkich wartości sekwencji

8.3.7.2. Function Parameters Echo¶

Complexity level: easy
Lines of code to write: 2 lines
Estimated time of completion: 3 min
Solution: solution/function_parameters_echo.py

English

Define function echo with two parameters
Parameter a is required
Parameter b is required
Wypisz a i b
Compare result with "Output" section (see below)

Polish

Zdefiniuj funkcję echo z dwoma parametrami
Parametr a jest wymagany
Parametr b jest wymagany
Wypisz a i b
Porównaj wyniki z sekcją "Output" (patrz poniżej)

Output

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

>>> echo(3, 4)
a=3 b=4

8.3.7.3. Function Parameters Default¶

Complexity level: easy
Lines of code to write: 6 lines
Estimated time of completion: 3 min
Solution: solution/function_parameters_default.py

English

Define function default with two parameters
Parameter a is required
Parameter b is optional and has default value None
If only one argument was passed, consider second equal to the first one
Print a i b
Compare result with "Output" section (see below)

Polish

Zdefiniuj funkcję default z dwoma parametrami
Parametr a jest wymagany
Parametr b jest opcjonalny i ma domyślną wartość None
Jeżeli tylko jeden argument był podany, przyjmij drugi równy pierwszemu
Wypisz a i b
Porównaj wyniki z sekcją "Output" (patrz poniżej)

Output

>>> default(1)
a=1 b=1

>>> default(2, 3)
a=2 b=3