Prerequisite: | class MyClass: # Hidden member MyClass __ hiddenVariable = 0 # Member method that changes # __hiddenVariable def add ( self , increment): self .__ hiddenVariable + = increment print ( self .__ hiddenVariable)
# Driver code myObject = MyClass () myObject.add ( 2 ) myObject.add ( 5 ) # This line raises an error print (myObject .__ hiddenVariable) |
Output:
2 7 Traceback (most recent call last): File "filename.py", line 13, in print (myObject .__ hiddenVariable) AttributeError: MyClass instance has no attribute ’__hiddenVariable’
In the above program, we tried access a hidden variable outside the class using an object and it threw an exception.
We can access the value of a hidden attribute using a tricky syntax:
| # Python program to demonstrate what’s hidden
# members can be accessed outside the class class MyClass: # Hidden member MyClass __ hiddenVariable = 10
# Driver code myObject = MyClass () print (myObject._MyClass__hiddenVariable) |
Output:
10
Private methods are available outside of their class, but not as easily accessible. Nothing in Python is truly private; internally, the private method and attribute names are mapped and unmangled on the fly to make them appear inaccessible by their given names [see this for the source].
Printing objects Printing objects gives us information about the objects with which we work. In C++, we can do this by adding a friend ostream & amp; operator
| class Test: def __ init __ ( self , a, b): self . a = a self . b = b def __ repr __ ( self ): retu rn "Test a:% sb:% s" % ( self . a, self .b) def __ str __ ( self ): return "From str method of Test : a is% s, " "b is% s" % ( self . a, self . b)
Driver code t = Test ( 1234 , 5678 ) print (t) # This calls __str __ () print ([t]) # This calls __repr __ () |
Exit:
From str method of Test: a is 1234, b is 5678 [Test a: 1234 b: 5678]
Important points about printing:
- If no __str__ method is defined, print t (or print str (t)) uses __repr__.
| class Test: def __ init __ ( self , a, b): self . a = a self . b = b def __ repr __ ( self ): return " Test a:% sb:% s " % ( self . a, self . b)
Driver code t = Test ( 1234 , 5678 ) print (t) |
Output:
Test a: 1234 b: 5678
- If no __repr__ method is defined, the default is used.
| class Test: def __ init __ ( self , a, b): self . a = a self . b = b
Driver code t = Test ( 1234 , 5678 ) print (t) |
Output:
This article courtesy of Shwetanshu Rohatgi . Please post comments if you find something wrong or if you would like to share more information on the topic discussed above.
