Python中descriptor的详细介绍

class RevealAccess(object):

  """A data descriptor that sets and returns values

    normally and prints a message logging their access.

  """

  def __init__(self, initval=None, name='var'):

    self.val = initval

    self.name = name

  def __get__(self, obj, objtype):

    print('Retrieving', self.name)

    return self.val

  def __set__(self, obj, val):

    print('Updating', self.name)

    self.val = val

>>> class MyClass(object):

...   x = RevealAccess(10, 'var "x"')

...   y = 5

...

>>> m = MyClass()

>>> m.x

Retrieving var "x"

10

>>> m.x = 20

Updating var "x"

>>> m.x

Retrieving var "x"

20

>>> m.y

5