8.15. Functional Callable

>>> def hello():
...     return 'Hello World'
>>>
>>>
>>> callable(hello)
True
>>>
>>> type(hello)
<class 'function'>
>>>
>>> hello  
<function hello at 0x...>
>>>
>>> hello()
'Hello World'

8.15.1. Calling Call Method

• __call__() method makes object callable

>>> def hello():
...     return 'Hello World'
>>>
>>>
>>> hello()
'Hello World'
>>>
>>> hello.__call__()
'Hello World'

8.15.2. Overloading Call Method

>>> data = str('Mark Watney')
>>>
>>> data()
Traceback (most recent call last):
TypeError: 'str' object is not callable
>>>
>>> callable(data)
False

>>> class str(str):
...     def __call__(self):
...         print('Calling str')
>>>
>>>
>>> data = str('Mark Watney')
>>>
>>> data()
Calling str
>>>
>>> callable(data)
True

8.15.3. Typing

>>> from typing import Callable
>>>
>>>
>>> def add(a: int, b: int) -> int:
...     return a + b
>>>
>>>
>>> total: Callable = add
>>> total: Callable[[int, int], int] = add

>>> from typing import Callable
>>>
>>>
>>> def lower() -> str:
...     return 'hello'
>>>
>>>
>>> def higher() -> Callable:
...     return lower

>>> from typing import Callable
>>>
>>>
>>> def fetch(url: str,
...           on_success: Callable = lambda: ...,
...           on_error: Callable = lambda: ...) -> None:
...     ...

>>> from typing import Callable
>>>
>>>
>>> def fetch(url: str,
...           on_success: Callable[[int,int], int],
...           on_error: Callable) -> callable:
...     ...
>>>
>>> def ok(x: int, y: int) -> int:
...     ...
>>>
>>> fetch('https://...',
...         on_success=ok,
...         on_error=lambda: ...)

>>> from typing import Callable, Iterator, Iterable
>>>
>>>
>>> def map(func: Callable, data: Iterable) -> Iterator:
...     ...
>>>
>>> def filter(func: Callable, data: Iterable) -> Iterator:
...     ...

8.15.4. Assignments

Code 8.27. Solution

"""
* Assignment: Functional Callable Define
* Complexity: easy
* Lines of code: 1 lines
* Time: 3 min

English:
    1. Define function `check` without any parameter
    2. Function `check` must return `wrapper: Callable`
    3. Run doctests - all must succeed

Polish:
    1. Zdefiniuj funkcję `check` bez żadnego parametru
    2. Funkcja `check` ma zwracać `wrapper: Callable`
    3. Uruchom doctesty - wszystkie muszą się powieść

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

    >>> assert isfunction(check)
    >>> assert isfunction(wrapper)
    >>> assert isfunction(check())

    >>> wrapper()
    'hello from wrapper'

    >>> check()()
    'hello from wrapper'
"""


def wrapper():
    return 'hello from wrapper'


# Without any parameter
# Returns wrapper function
# type: Callable[[Callable], Callable]
def check():
    ...