Data hiding

In Python, we use double underscore (Or __) before the attributes name and those attributes will not be directly visible outside.

class MyClass:

# Hidden member of MyClass
__hiddenVariable = 0

# A 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 causes 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 to access hidden variable outside the class using object and it threw an exception.

We can access the value of hidden attribute by a tricky syntax:

# A Python program to demonstrate that hidden
# members can be accessed outside a class
class MyClass:

# Hidden member of MyClass
__hiddenVariable = 10

# Driver code
myObject = MyClass()
print(myObject._MyClass__hiddenVariable)
Output :

10
Private methods are accessible outside their class, just not easily accessible. Nothing in Python is truly private; internally, the names of private methods and attributes are mangled and unmangled on the fly to make them seem inaccessible by their given names [See this for source ].

Printing Objects

Printing objects gives us information about objects we are working with. In C++, we can do this by adding a friend ostream& operator << (ostream&, const Foobar&) method for the class. In Java, we use toString() method. In python this can be achieved by using __repr__ or __str__ methods.

class Test:
def __init__(self, a, b):
self.a = a
self.b = b

def __repr__(self):
return "Test a:%s b:%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__()
Output :

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:%s b:%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 then 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 :

<__main__.Test instance at 0x7fa079da6710>