Data Hiding in Python

An object's attributes may or may not be visible outside the class definition. You need to name attributes with a double underscore prefix, and those attributes then are not be directly visible to outsiders.

Example

#!/usr/bin/python
class JustCounter:
   __secretCount = 0
   def count(self):
      self.__secretCount += 1
      print self.__secretCount
counter = JustCounter()
counter.count()
counter.count()
print counter.__secretCount

Output

When the above code is executed, it produces the following result −

1
2
Traceback (most recent call last):
   File "test.py", line 12, in <module>
      print counter.__secretCount
AttributeError: JustCounter instance has no attribute '__secretCount'

Python protects those members by internally changing the name to include the class name. You can access such attributes as object._className__attrName. If you would replace your last line as following, then it works for you −

.........................
print counter._JustCounter__secretCount

When the above code is executed, it produces the following result −

1
2
2