Python error while initializing a class derived from and abstract
I have this simple code and I am getting a strange error:
from abc import ABCMeta, abstractmethod
class CVIterator(ABCMeta):
def __init__(self):
self.n = None # the value of n is obtained in the fit method
return
class KFold_new_version(CVIterator): # new version of KFold
def __init__(self, k):
assert k > 0, ValueError('cannot have k below 1')
self.k = k
return
cv = KFold_new_version(10)
In [4]: ---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-4-ec56652b1fdc> in <module>()
----> 1 __pyfile = open('''/tmp/py13196IBS''');exec(compile(__pyfile.read(), '''/home/donbeo/Desktop/prova.py''', 'exec'));__pyfile.close()
/home/donbeo/Desktop/prova.py in <module>()
19
20
---> 21 cv = KFold_new_version(10)
TypeError: __new__() missing 2 required positional arguments: 'bases' and 'namespace'
What am I doing wrong? A theoretical explanation would be appreciated.
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1 answer
You have used the meta tag incorrectly ABCMeta
. This is a meta class, not a base class. Use it as such.
For Python 2, this means assigning an attribute __metaclass__
to it for the class:
class CVIterator(object):
__metaclass__ = ABCMeta
def __init__(self):
self.n = None # the value of n is obtained in the fit method
In Python 3, you must use the syntax metaclass=...
when defining a class:
class CVIterator(metaclass=ABCMeta):
def __init__(self):
self.n = None # the value of n is obtained in the fit method
As with Python 3.4, you can use a abc.ABC
helper class as your base class:
from abc import ABC
class CVIterator(ABC):
def __init__(self):
self.n = None # the value of n is obtained in the fit method
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