In [37]:

    

# How do the dot operator work in Python

from holding import Holding


h = Holding('AA', '201608-09', 100, 67.9)


    

In [38]:

    

h.name


    

    
Out[38]:





'AA'

In [39]:

    

h.shares


    

    
Out[39]:





100






    
Out[39]:





100

In [40]:

    

# What is happening under the hood when dot operator is used
"""
-- Every instance has a __dict__ attributes that keeps a record of the instance attributes.
"""
h.__dict__


    

    
Out[40]:





{'date': '201608-09', 'name': 'AA', 'price': 67.9, 'shares': 100}






    
Out[40]:





{'date': '201608-09', 'name': 'AA', 'price': 67.9, 'shares': 100}

In [41]:

    

# Any operation on the instance attribute uses the __dict__ attribute to access the attribute
h.__dict__['name']


    

    
Out[41]:





'AA'






    
Out[41]:





'AA'

In [42]:

    

h.__dict__['shares']


    

In [43]:

    

# Add a new attribute
h.__dict__['yow'] = 'dummy'


    

In [44]:

    

h.yow


    

    
Out[44]:





'dummy'

In [45]:

    

h.__dict__


    

    
Out[45]:





{'date': '201608-09',
 'name': 'AA',
 'price': 67.9,
 'shares': 100,
 'yow': 'dummy'}

In [46]:

    

del h.__dict__['yow']


    

In [46]:

    

h.__dict__


    

    
Out[46]:





{'date': '201608-09', 'name': 'AA', 'price': 67.9, 'shares': 100}

In [48]:

    

# The functions in the class are not part of the __dict__ of the instance
# It is part of the __dict__ attribute of the class
h.__class__.__dict__


    

In [49]:

    

Holding.__dict__


    

In [50]:

    

# Here also when the function is accessed, the __dict__ attribute is used under the hood.
h.cost()


    

In [51]:

    

# The above is equivalent to 
Holding.__dict__['cost'](h)


    

    
Out[51]:





6790.000000000001

In [52]:

    

# Python does not impose restriction on adding, setting attributes
# There is no notion of private, protected attributes
# So how to ensure this in Python. This is what we are going to learn next.


    

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