Prerequisite : Object Oriented Programming in Python | Set 1 (Class, Object and Members)
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 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__.
classTest:def__init__(self, a, b):self.a=aself.b=bdef__repr__(self):return"Test a:%s b:%s"%(self.a,self.b)# Driver Codet=Test(1234,5678)print(t)chevron_rightfilter_noneOutput :
Test a:1234 b:5678
-
If no __repr__ method is defined then the default is used.
classTest:def__init__(self, a, b):self.a=aself.b=b# Driver Codet=Test(1234,5678)print(t)chevron_rightfilter_noneOutput :
<__main__.Test instance at 0x7fa079da6710>
This article is contributed by Shwetanshu Rohatgi. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
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