据我了解，Python 模块 abc 应该防止实例化未实现基类的所有标记方法@abstractmethod类（前提是基类已设置__metaclass__ = ABCMeta）
但是，这似乎不适用于以下代码：
抽象基类：
""" Contains payment processors for executing payments """
from abc import ABCMeta, abstractmethod
class AbstractPaymentProcessor:
""" Abstract class for executing faucet Payments
Implement this at your own. Possible implementations include
online wallets and RPC calls to running dogecoin wallets """
__metaclass__ = ABCMeta
@abstractmethod
def execute_payment(self, destination_address, amount):
""" Execute a payment to one receiving single address
return the transaction id or None """
pass
@abstractmethod
def execute_multi_payment(self, destination_addresses, amounts):
""" Execute a payment to multiple receiving addresses
return the transaction id or None """
pass
@abstractmethod
def get_transaction_status(self):
""" Get the status of the transaction
Indicate if transaction is already confirmed. Return
- True if confirmed
- False if unconfirmed
- None if transaction doesn't exist (or raise exception?)"""
pass
@abstractmethod
def get_available_balance(self):
""" Get the available balance
i.e. how much "cash" is in the faucet """
pass
子类缺少方法：
""" Contains a logging payment processor """
import logging
import random
from AbstractPaymentProcessor import AbstractPaymentProcessor
class DummyLoggingPaymentProcessor (AbstractPaymentProcessor):
""" Payment processor that does nothing, just logs """
def __new__(self):
self._logger = logging.getLogger(__name__)
self._logger.setLevel(logging.INFO)
def execute_payment(self, destination_address, amount):
""" Execute a payment to one receiving single address
return the transaction id or None """
raise NotImplementedError("Not implemented yet")
def execute_multi_payment(self, destination_addresses, amounts):
""" Execute a payment to multiple receiving addresses
return the transaction id or None """
raise NotImplementedError("Not implemented yet")
def get_transaction_status(self):
""" Get the status of the transaction
Indicate if transaction is already confirmed. Return
- True if confirmed
- False if unconfirmed
- None if transaction doesn't exist """
raise NotImplementedError("Not implemented yet")
if __name__ == '__main__':
# can instanciate, although get_available_balance is not defined. Why? abc should prevent this!?
c = DummyLoggingPaymentProcessor()
c.get_available_balance()
子类可以在（相当粗糙的）测试代码中实例化。为什么会这样？
我正在使用Python 2.7。
你正在覆盖__new__;正是这个方法（在object.__new__上）阻止了实例化。
您没有在此处创建不可变类型，否则正在更改新对象的创建，因此请改用__init__：
def __init__(self):
self._logger = logging.getLogger(__name__)
self._logger.setLevel(logging.INFO)
无论如何，你都用错__new__;传入的第一个参数是类，而不是实例，因为当时没有创建实例。通过覆盖__new__而不调用原始实例，您 a） 不会创建实例，并且 b） 不会触发阻止首先创建实例的代码。
使用 __init__ 而不是__new__实例化会按预期引发异常：
>>> class DummyLoggingPaymentProcessor (AbstractPaymentProcessor):
... """ Payment processor that does nothing, just logs """
... def __init__(self):
... self._logger = logging.getLogger(__name__)
... self._logger.setLevel(logging.INFO)
... def execute_payment(self, destination_address, amount):
... """ Execute a payment to one receiving single address
...
... return the transaction id or None """
... raise NotImplementedError("Not implemented yet")
... def execute_multi_payment(self, destination_addresses, amounts):
... """ Execute a payment to multiple receiving addresses
...
... return the transaction id or None """
... raise NotImplementedError("Not implemented yet")
... def get_transaction_status(self):
... """ Get the status of the transaction
...
... Indicate if transaction is already confirmed. Return
... - True if confirmed
... - False if unconfirmed
... - None if transaction doesn't exist """
... raise NotImplementedError("Not implemented yet")
...
>>> c = DummyLoggingPaymentProcessor()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Can't instantiate abstract class DummyLoggingPaymentProcessor with abstract methods get_available_balance