Python abstract attribute and inheritance

Question

Say I have the following code:

class Archive(object):
 """ Archiv-File wrapper """
 READ_MODE = 0
 WRITE_MODE = 1
 def __init__(self, file_):
 self.file_ = file_
 self._mode = None
 @property
 def mode(self):
 return self._mode
 @mode.setter
 def mode(self, value):
 self._mode = value
 def open(self, mode="r", pwd=None):
 raise NotImplemented("Subclasses should implement this method!")
 def close(self):
 raise NotImplemented("Subclasses should implement this method!")
################################################
class GzipGPGArchive(Archive):
 READ_MODE = 'r:gz' # Open for reading with gzip compression.
 WRITE_MODE = 'w:gz' # Open for gzip compressed writing.
 SUFFIX = "tar.gz.gpg"
 def __init__(self, *args, **kwargs):
 super(GzipGPGArchive, self).__init__(*args, **kwargs)
 @mode.setter # This causes unresolved reference
 def mode(self, value):
 # do internal changes
 self._mode = value
 def open(self):
 pass
 def close(self):
 pass

so know what is the best pythonic way to override the setter and getter method of the Abstract class attribute mode.

Overriding @mode.setter in the sub-class GzipGPGArchive causes unresolved reference!

• CristiFati: You might want to initialize self._mode in the initializer (__init__), otherwise after creating an instance you try to read the property (before setting it) you'll get an AttributeError.
• arash javanmard: @CristiFati corrected it, thanks

Answer 1

First of all, there is no such thing as abstract attributes in Python. You can achieve abstraction, however, by using abc module. Perhaps it is not really "pythonic", but it works.

This is the minimal example with inheritance and abstraction. Use it as as template:

from abc import ABCMeta, abstractmethod
class Mother(metaclass=ABCMeta):
 @abstractmethod
 def method_(self):
 pass
 @property
 @abstractmethod
 def property_(self):
 return -1
 @property_.setter
 @abstractmethod
 def property_(self, value):
 pass
class Daughter(Mother):
 def __init__(self):
 self.value_ = 0
 def method_(self):
 print(self.value_)
 @property
 def property_(self):
 return = self.value_
 @property_.setter
 def property_(self, value):
 self.value_ = value

• arash javanmard: this worked for me, BUT what is really the right pythonic to doing such a things???