3.12. FuncProg Callable¶
>>> def hello():
... return 'Hello World'
>>>
>>>
>>> callable(hello)
True
>>>
>>> type(hello)
<class 'function'>
>>>
>>> hello
<function hello at 0x...>
>>>
>>> hello()
'Hello World'
3.12.1. Calling Call Method¶
__call__()
method makes object callable
>>> def hello():
... return 'Hello World'
>>>
>>>
>>> hello()
'Hello World'
>>>
>>> hello.__call__()
'Hello World'
3.12.2. 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
3.12.3. Callbacks¶
Callback Design Pattern:
>>> def request(url, on_success, on_error):
... try:
... result = f'Downloading from {url}'
... except Exception as error:
... on_error(error)
... else:
... on_success(result)
>>>
>>>
>>> request(
... url='https://python.astrotech.io',
... on_success=lambda result: print(result),
... on_error=lambda error: print(error))
Downloading from https://python.astrotech.io
>>> from http import HTTPStatus
>>> import requests
>>>
>>>
>>> def http_request(url, on_success=lambda: ..., on_error=lambda: ...):
... result = requests.get(url)
... if result.status_code == HTTPStatus.OK:
... return on_success(result)
... else:
... return on_error(result)
>>>
>>>
>>> http_request(
... url='http://python.astrotech.io/',
... on_success=lambda result: print(result),
... on_error=lambda error: print(error))
<Response [200]>
3.12.4. Type Annotation¶
>>> 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 http_request(url: str,
... on_success: Callable = lambda: ...,
... on_error: Callable = lambda: ...) -> None:
... ...
>>> from typing import Callable
>>>
>>>
>>> def request(url: str,
... on_success: Callable[[int,int], int],
... on_error: Callable) -> callable:
... ...
>>>
>>> def handle_success(x: int, y: int) -> int:
... ...
>>>
>>> request('https://...',
... on_success=handle_success,
... on_error=lambda: ...)
>>> from typing import Callable, Iterator, Iterable
>>>
>>>
>>> def map(func: Callable, data: Iterable) -> Iterator:
... ...
>>>
>>> def filter(func: Callable, data: Iterable) -> Iterator:
... ...
3.12.5. Assignments¶
"""
* Assignment: FuncProg Callable Define
* Complexity: easy
* Lines of code: 4 lines
* Time: 5 min
English:
1. Define function `wrapper`
2. Function `wrapper` takes arbitrary number of positional
and keyword arguments
3. Function `wrapper` returns 'hello from wrapper'
4. Define function `check` with `func: Callable` as a parameter
5. Function `check` must return `wrapper: Callable`
6. Run doctests - all must succeed
Polish:
1. Zdefiniuj funkcję `wrapper`
2. Funkcja `wrapper` przyjmuje dowolną ilość argumentów pozycyjnych
i nazwanych
3. Funkcja `wrapper` zwraca 'hello from wrapper'
4. Zdefiniuj funkcję `check` z `func: Callable` jako parametr
5. Funkcja `check` ma zwracać `wrapper: Callable`
6. 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(lambda: ...))
>>> check(lambda: ...)()
'hello from wrapper'
"""
# Takes arbitrary number of positional and keyword arguments
# Returns 'hello from wrapper'
# type: Callable[[], str]
def wrapper():
...
# Takes `func` as an argument, returns wrapper function
# type: Callable[[Callable], Callable]
def check():
...