在Python2.7中,此代码可以很好地运行,__getattr__
MetaTable
会跑。但是在Python 3.5中它不起作用。
class MetaTable(type):
def __getattr__(cls, key):
temp = key.split("__")
name = temp[0]
alias = None
if len(temp) > 1:
alias = temp[1]
return cls(name, alias)
class Table(object):
__metaclass__ = MetaTable
def __init__(self, name, alias=None):
self._name = name
self._alias = alias
d = Table
d.student__s
但是在Python 3.5中,我得到了一个属性错误:
Traceback (most recent call last):
File "/Users/wyx/project/python3/sql/dd.py", line 31, in <module>
d.student__s
AttributeError: type object 'Table' has no attribute 'student__s'
答案 0 :(得分:29)
不再检查Python 3 changed how you specify a metaclass,__metaclass__
。
在班级签名中使用metaclass=...
:
class Table(object, metaclass=MetaTable):
演示:
>>> class MetaTable(type):
... def __getattr__(cls, key):
... temp = key.split("__")
... name = temp[0]
... alias = None
... if len(temp) > 1:
... alias = temp[1]
... return cls(name, alias)
...
>>> class Table(object, metaclass=MetaTable):
... def __init__(self, name, alias=None):
... self._name = name
... self._alias = alias
...
>>> d = Table
>>> d.student__s
<__main__.Table object at 0x10d7b56a0>
如果您需要在代码库中为Python 2和3提供支持,则可以使用six.with_metaclass()
baseclass generator或@six.add_metaclass()
class decorator来指定元类。