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我有一个对象，它封装了具有某些特征的网络配置文件。例如，我的个人资料有一个Connection并且取决于它，它可能有也可能没有IP选项（static或dhcp）。

因此，我的第一次尝试是使用从dict扩展的普通类并添加一些辅助函数：

class Profile(dict):
    IP_CONNECTIONS = ('ethernet', 'wireless', 'pppoe')
    def is_ethernet(self): return self['Connection'] == 'ethernet'
    def is_wireless(self): return self['Connection'] == 'wireless'
    def is_wireless_adhoc(self): return self.is_wireless() and 'AdHoc' in self
    def has_ip(self)
        return self['Connection'] in self.IP_CONNECTIONS
    def has_ip_static(self)
        if not self.has_ip():
            return False
        if self.is_ipv4():
            return self['IP'] == 'static'
        if self.is_ipv6():
            return self['IP6'] == 'static'
        return False
    def has_ip_dhcp(self):
        if not self.has_ip():
            return False
        if self.is_ipv4():
            return self['IP'] == 'dhcp'
        if self.is_ipv6():
            return self['IP6'] == 'dhcp' or self['IP6'] == 'dhcp-noaddr'
        return False
    def is_ipv4(self): return self.has_ip() and 'IP' in self
    def is_ipv6(self): return self.has_ip() and 'IP6' in self
    def get_client(self):
        if self.has_ip_dhcp() and 'DHCPClient' in self:
            return self['DHCPClient']
        return None

is_*这行得通，但我有一个庞大的班级，有很多has_*特色功能。它们中的大多数只会用于非常特定的配置文件，并且False大部分时间都会返回。

然后我想到我可以用继承来描述特征。

__new__在尝试并未能实现元类后，因为调用该方法时数据尚不可用。我想出了这样的事情：

def load_profile(filename):
    data = _read_profile(filename)
    bases = _classify_profile(data)
    baseclass = type('Profile', bases, {})
    return baseclass(data)

class IP:
    CONNECTIONS = ('ethernet', 'wireless')
class IPv4(IP):
    def is_static(self):
        return self['IP'] == 'static'
class IPv6(IP):
    def is_static(self):
        return self['IP6'] == 'static'
class DHCP:
    def get_client(self):
        return self['DHCPClient'] if 'DHCPClient' in self else None

class Wireless:
    def is_adhoc(self):
        return 'AdHoc' in self

def _classify_profile(data):
    classes = [dict]

    if data['Connection'] == 'wireless':
        classes.append(Wireless)
    if data['Connection'] in IP.CONNECTIONS:
        if 'IP' in data:
            classes.append(IPv4)
            if data['IP'] == 'dhcp':
                classes.append(DHCP)
        if 'IP6' in data:
            classes.append(IPv6)
            if data['IP6'] == 'dhcp' or data['IP6'] == 'dhcp-noaddr':
                classes.append(DHCP)

    return tuple(classes)

以前我在做的时候profile.has_ip()，现在我只是用isinstance(profile, IP). 在我看来，通过良好的责任分离，这一点更加清晰。

问题：这是实现动态继承的好方法吗？这样做的pythonic方式是什么？

提前致谢！

4

1 回答 1

0

我真的不知道动态继承是什么意思，但我会这样写：

base_classes = []

class IP(dict):
    CONNECTIONS = ('ethernet', 'wireless')
    def is_static(self):
        raise NotImplementedError('To be implemented in subclasses.') 
    @classmethod
    def wants_the_meaningful_named_data(cls, data):
        return False
base_classes.append(IP)

class IPv4(IP):
    def is_static(self):
        return self['IP'] == 'static'
    @classmethod
    def wants_the_meaningful_named_data(cls, data):
        return data['Connection'] in cls.CONNECTIONS and 'IP' in data
base_classes.append(IPv4)

class IPv6(IP):
    def is_static(self):
        return self['IP6'] == 'static'
    @classmethod
    def wants_the_meaningful_named_data(cls, data):
        return data['Connection'] in cls.CONNECTIONS and 'IP6' in data
base_classes.append(IPv6)

def load_profile(filename):
    data = _read_profile(filename)
    for base_class in base_classes:
        if base_class.wants_the_meaningful_named_data(data):
            return base_class(data)
    return dict(data)

我喜欢这样的东西。我认为没有必要进入元类。

于 2013-10-08T19:04:13.310 回答