Python Underscores Part 2

Trailing underscores

var_

Well, trailing underscores are used only for giving Python's keyword names to variables.

Example:

print_ 
#instead of print 

while_ 
#instead of while

Double leading (dunders) underscores

__var

Avoid naming conflicts in subclasses by rewriting the name of a class attribute in a class context — name mangling. The attribute would be protected from being overridden.

Example:

class Parent: 
     def __init__(self): 
        self.foo = 11 
        self.__baz = 23 

t = Parent() 
print(dir(t))

As an output we get:

['_Parent__baz', '__class__',
'__delattr__', '__dict__',
'__dir__', '__doc__', '__eq__',
'__format__', '__ge__',
'__getattribute__', '__gt__',
'__hash__', '__init__', '__le__',
'__lt__', '__module__', '__ne__',
'__new__', '__reduce__',
'__reduce_ex__', '__repr__',
'__setattr__', '__sizeof__',
'__str__', '__subclasshook__',
'__weakref__', 'foo']

Example:

class Child(Parent): 
    def __init__(self): 
       super().__init__() 
       self.foo = 'overridden' 
       self.__baz = 'overridden' 
       
t2 = Child() 

t2.foo 
# overriden
 
t2.__baz
# AttributeError: 
#"'Child' object has no attribute '__baz'"

Let's continue exploring the chunk of code from the example:

print(dir(t2)) 
#a long list of attributes 

t2._Child__baz 
# ovverriden 

t2._Parent__baz 
# result is 42

We have noticed the variables that are reserved by using dir().

The name mangling is transparent to a programmer. That my seem confusing, right?

Example:

class ManglingTest: 
    def __init__(self): 
       self.__mangled = 'hello' 
       
    def get_mangled(self): 
       return self.__mangled 
       
ManglingTest().get_mangled() 
# 'hello' 

ManglingTest().__mangled 
# AttributeError: 
#"'ManglingTest' object has no attribute '__mangled'"

We are getting access via the class method that uses the original name.

That's a lot to consume.

Spend a little time and play with the example to get it more clearly. I know that you can get it.

Good luck in your exploration.👍🏼