Python has a "really hidden encapsulation"?

dmytro starosud d.starosud at gmail.com
Thu Oct 21 18:49:14 CEST 2010


Hello,
I'm Python beginner (from Ukraine).
I may have found the way to really hide attributes in Python class.
The whole control on this attribute is implemented inside of the
class.
*(code is below, Python 3)
You see that we can't get the reference to instance of class
"en_property" outside the class "segment", but in the inside we can.

*It seems like there is no way to get the reference to field
“en_property.v_min” or “en_property.v_max”.
And object “s” has “two” attributes “v_min”: “s.__dict__['v_min']” and
“s.v_min”.

Help me find the answer, Can I change this hidden attribute outside
the class?
Or is it just an interesting feature?
...and Python has a "really hidden encapsulation"?

code:
class en_property(property):
   ptr_pget = None
   ptr_pset = None

   def pset(self, _class, value):
       self.ptr_pset(self, _class, value)

   def pget(self, _class):
       return self.ptr_pget(self, _class)

   def __init__(self, pget, pset):
       property.__init__(self, self.pget, self.pset)
       self.ptr_pget = pget
       self.ptr_pset = pset

class segment():
   def min_set(prop, self, p_min):
       if (self.v_max is not None) and (p_min > self.v_max):
           raise AttributeError('It must be: "min < max"')
       else:
           prop.v_min = p_min

   def min_get(prop, self):
       if 'v_min' in dir(prop):
           return prop.v_min

   def max_set(prop, self, p_max):
       if (self.v_min is not None) and (p_max < self.v_min):
           raise AttributeError('It must be: "min < max"')
       else:
           prop.v_max = p_max

   def max_get(prop, self):
       if 'v_max' in dir(prop):
           return prop.v_max

   v_min = en_property(min_get, min_set)
   del min_set, min_get
   v_max = en_property(max_get, max_set)
   del max_set, max_get

............................................................................
>>> s = segment()
>>> s.v_min = -1
>>> s.v_max = 1
>>> s.v_min = 2
Traceback (most recent call last):
 File "<interactive input>", line 1, in <module>
 File "D:\_dimka\I_Master\Programs_PyPg\enca.py", line 6, in pset
   self.ptr_pset(self, _class, value)
 File "D:\_dimka\I_Master\Programs_PyPg\enca.py", line 19, in min_set
   raise AttributeError('It must be: "min < max"')
AttributeError: It must be: "min < max"
>>> s.__dict__['v_min'] = 2
>>> s.__dict__['v_min']
2
>>> s.v_min
-1
>>>



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