Is this a bug in Python inheritance?

Question

I'm not sure if the output of this code is correct or a bug:

class F:
  """An abstract class"""
  list_of_secrets = []
  def __init__(self):
    pass

  def getSecret(self):
    return self.list_of_secrets

class F_None(F):
  pass

class F_Some(F):
  def __init__(self):
    self.list_of_secrets.append("secret value!")

x = F_Some()
print "x:",x.getSecret()

y = F_None()
print "y:",y.getSecret()

The output using python 2.7.3:

x: ['secret value!']

y: ['secret value!']

I think it should output:

x: ['secret value!']

y: []

Any thoughts?

I'm not sure if it is the same, since there is no inheritance involved. — user1234299, Feb 25 '13 at 12:51
It is the same. It is still a class attribute, not an instance attribute. A parent class in this case, but still the exact same situation. — Martijn Pieters, Feb 25 '13 at 12:52

score 2 · Answer 1 · answered Feb 25 '13 at 12:50

2

list_of_secrets is scoped to the class here. You want to instead attach it to self in __init__

  def __init__(self):
      self.list_of_secrets = []

answered Feb 25 '13 at 12:50

Doug T.

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score 1 · Answer 2 · answered Feb 25 '13 at 12:50

You never define self.list_of_secrets. You only define F.list_of_secrets, which is entirely different. Do this instead:

class F:
  """An abstract class"""
  def __init__(self):
    self.list_of_secrets = []

  def getSecret(self):
    return self.list_of_secrets

Is this a bug in Python inheritance?

2 Answers2