12.3. Function Parameters¶
12.3.1. Rationale¶
Parameter - Receiving variable used within the function
Required parameter:
Necessary to call that function
Specified at leftmost side
Default parameter:
Optional to call that function
Has default value
Default value will be overridden if specified at a call time
Specified at rightmost side
12.3.2. Syntax¶
Function definition with parameters:
def myfunction(<parameters>):
<do something>
>>> def add(a, b):
... print(a + b)
12.3.3. Required Parameters¶
Parameters without default values are required
>>> def add(a, b):
... print(a + b)
>>>
>>>
>>> add()
Traceback (most recent call last):
TypeError: add() missing 2 required positional arguments: 'a' and 'b'
>>> add(1)
Traceback (most recent call last):
TypeError: add() missing 1 required positional argument: 'b'
>>> add(1, 2)
3
>>> add(1, 2, 3)
Traceback (most recent call last):
TypeError: add() takes 2 positional arguments but 3 were given
12.3.4. 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)
Traceback (most recent call last):
TypeError: add() takes from 0 to 2 positional arguments but 3 were given
12.3.5. 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()
Traceback (most recent call last):
TypeError: add() missing 1 required positional argument: 'a'
>>> add(1)
21
>>> add(1, 2)
3
>>> add(1, 2, 3)
Traceback (most recent call last):
TypeError: add() takes from 1 to 2 positional arguments but 3 were given
>>> def add(a=1, b):
... print(a + b)
Traceback (most recent call last):
SyntaxError: non-default argument follows default argument
>>> def add(a, b=1, c):
... print(a + b + c)
Traceback (most recent call last):
SyntaxError: non-default argument follows default argument
12.3.6. Examples¶
Example 1:
>>> def add(a, b):
... print(a + b)
>>>
>>>
>>> add(1, 2)
3
>>> add(1.5, 2.5)
4.0
>>> add('a', 'b')
ab
Example 2:
>>> def echo(text):
... print(text)
>>>
>>>
>>> echo('hello')
hello
Example 3:
>>> def connect(username, password, host='127.0.0.1', port=22,
... ssl=True, keep_alive=1, persistent=False):
...
... print('Connecting...')
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...')
12.3.7. Assignments¶
"""
* Assignment: Function Parameters Sequence
* Required: yes
* Complexity: easy
* Lines of code: 2 lines
* Time: 3 min
English:
1. Define function `total`
2. Function parameter is `data` sequence of integers
3. Function returns sum of all values in sequence
4. Run doctests - all must succeed
Polish:
1. Zdefiniuj funkcję `total`
2. Parametrem do funkcji jest `data` sekwencja liczb
3. Funkcja zwraca sumę wszystkich wartości z sekwencji
4. Uruchom doctesty - wszystkie muszą się powieść
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> from inspect import isfunction
>>> isfunction(total)
True
>>> type(total([0, 1])) is int
True
>>> type(total([0.0, 1.1])) is float
True
>>> total([1,2,3])
6
>>> total([1,2,3,4,5,6])
21
>>> total(range(0,101))
5050
"""
"""
* Assignment: Function Parameters Echo
* Required: yes
* Complexity: easy
* Lines of code: 2 lines
* Time: 3 min
English:
1. Define function `echo` with two parameters
2. Parameter `a` is required
3. Parameter `b` is required
4. Return `a` and `b` as a `tuple`
5. Run doctests - all must succeed
Polish:
1. Zdefiniuj funkcję `echo` z dwoma parametrami
2. Parametr `a` jest wymagany
3. Parametr `b` jest wymagany
4. zwróć `a` i `b` jako `tuple`
5. Uruchom doctesty - wszystkie muszą się powieść
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> from inspect import isfunction
>>> isfunction(echo)
True
>>> type(echo(0,0)) is tuple
True
>>> echo(1, 2)
(1, 2)
>>> echo(3, 4)
(3, 4)
"""
"""
* Assignment: Function Parameters Default
* Required: yes
* Complexity: easy
* Lines of code: 4 lines
* Time: 3 min
English:
1. Define function `default` with two parameters
2. Parameter `a` is required
3. Parameter `b` is optional and has default value `None`
4. If only one argument was passed, consider second equal to the first one
5. Return `a` and `b` as a `dict`
6. Run doctests - all must succeed
Polish:
1. Zdefiniuj funkcję `default` z dwoma parametrami
2. Parametr `a` jest wymagany
3. Parametr `b` jest opcjonalny i ma domyślną wartość `None`
4. Jeżeli tylko jeden argument był podany, przyjmij drugi równy pierwszemu
5. Zwróć `a` i `b` jako `dict`
6. Uruchom doctesty - wszystkie muszą się powieść
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> from inspect import isfunction
>>> isfunction(default)
True
>>> type(default(0,0)) is dict
True
>>> default(1)
{'a': 1, 'b': 1}
>>> default(2, 3)
{'a': 2, 'b': 3}
"""