Интерфейсы в Python
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This document discusses various Python interfaces and design patterns including duck typing, abstract base classes (ABC), collections.abc, inheritance, and the Zope interface system. Duck typing allows objects to be used if they have the required attributes and methods without needing to inherit from a base class. ABCs allow defining abstract methods that must be implemented in subclasses. Collections provide common interfaces for types like mappings, sequences, sets, etc. The Zope interface system uses explicit interfaces that classes can declare they implement.
![Iterable
● __iter__ class A:
def __getitem__(self, i):
● __getitem__ if i < 3:
пока не IndexError return i
raise IndexError("out
of range")
>>> a = A()
>>> i = iter(a)
>>> list(i)
[0, 1, 2]](https://image.slidesharecdn.com/abc-120917031141-phpapp02/85/Python-5-320.jpg)
![Самодельное множество
from collections import Set >>> s1 = S({1, 2})
class S(Set): >>> 2 in s1
def __init__(self, s): True
super().__init__()
>>> s2 = S({2, 3})
self.s = frozenset(s)
>>> s3 = s1|s2
def __contains__(self, i):
>>> list(s3)
return i in self.s
[1, 2, 3]
def __iter__(self):
return iter(self.s) >>> s4 = s1 - s2
def __len__(self): >>> list(s4)
return len(self.s) [1]](https://image.slidesharecdn.com/abc-120917031141-phpapp02/85/Python-10-320.jpg)
Интерфейсы в Python
- 1. Интерфейсы Andrew Svetlov andrew.svetlov@gmail.com asvetlov.blogspot.com
- 2. Интерфейсы ● Duck Typing ● ABC ● Zope Interface
- 3. Duck Typing class A: >>> a = A() def f(self): >>> b = B(); print('A.f') >>> a.f() class B: A.f def f(self): >>> b.f() print('B.f') b.f
- 4. Pro/Contra ● Естественная ● Неявность запись интерфейса ● Ничего лишнего ● Сложность само- ● hasattr vs isinstance документирования ● a.x => Point ???
- 5. Iterable ● __iter__ class A: def __getitem__(self, i): ● __getitem__ if i < 3: пока не IndexError return i raise IndexError("out of range") >>> a = A() >>> i = iter(a) >>> list(i) [0, 1, 2]
- 6. Конструктор dict ● Аргумент может быть: ● dict ● Sequence of 2-elem sequences ● Mapping??? .keys!!! ● Iterable
- 7. Наследование class Base: def f(self): raise NotImplementedError() class A(Base): def f(self): return 1 >>> a = A() >>> isinstance(a, Base) True >>> b = Base() # ???
- 8. ABC (Abstract Base Classes) class Base(abc.Meta): @abc.abstractmethod def f(self): return 0 class A(Base): def f(self): return super().f() + 1 >>> a = A() >>> isinstance(a, Base) True >>> b = Base() # ??? Can't instantiate abstract class Base with abstract methods f >>> a.f() 1
- 9. collections.abc ● Hashable ● Mapping ● Iterable ● MutableMapping ● Iterator ● MappingView ● Sized ● KeysView ● Container ● ItemsView ● Callable ● Set ● ValuesView ● MutableSet ● Sequence ● ByteString ● MutableSequence
- 10. Самодельное множество from collections import Set >>> s1 = S({1, 2}) class S(Set): >>> 2 in s1 def __init__(self, s): True super().__init__() >>> s2 = S({2, 3}) self.s = frozenset(s) >>> s3 = s1|s2 def __contains__(self, i): >>> list(s3) return i in self.s [1, 2, 3] def __iter__(self): return iter(self.s) >>> s4 = s1 - s2 def __len__(self): >>> list(s4) return len(self.s) [1]
- 11. Необязательные методы ● Наличие метода ● Проверка на None ● Исключение NotImplementedError ● Значение NotImplemented
- 12. Наличие метода и None class A: class B(A): post = None def pre(self): def do(self): print('B.pre') if hasattr(self, def post(self): 'pre'): print('B.post') self.pre() print('A.do') if self.post is not None: >>> b = B() self.post() >>> b.do() >>> a = A() B.pre >>> a.do() A.do A.do B.post
- 13. NotImplementedError class A: class B(A): def pre(self): def pre(self): raise NotImplementedError( print('B.pre') 'implement pre method') def do(self): >>> a = A() try: >>> a.do() self.pre() A.do except NotImplementedError: >>> b = B() pass print('A.do') >>> b.do() B.pre a.do
- 14. NotImplemented class A: class B: def override(self): def override(self): return NotImplemented return 'overriden' def do(self): >>> a = A() val = self.override() >>> a.do() if (val is not NotImplemented): 'default' return val >>> b = B() else: >>> b.do() return 'default' 'overriden'
- 15. Zope Interface class IFile(Interface): body = Attribute('Contents of the file.') class ISize(Interface): def getSize(): 'Return the size of an object.' class File(object): implements(IFile) body = 'foo bar' class FileSize(object): implements(ISize) __used_for__ = IFile def __init__(self, context): self.context = context def getSize(self): return len(self.context.body)
- 16. Адаптеры registry = AdapterRegistry() def hook(provided, obj): adapter = registry.lookup1(providedBy(obj), provided, '') return adapter(object) adapter_hooks.append(hook) >>> file = File() >>> size = ISize(file) >>> size.getSize()
- 17. Вопросы? Andrew Svetlov andrew.svetlov@gmail.com asvetlov.blogspot.com