In [1]:

    

from IPython.display import display
from IPython.display import HTML
import IPython.core.display as di # Example: di.display_html('<h3>%s:</h3>' % str, raw=True)

# This line will hide code by default when the notebook is exported as HTML
di.display_html('<script>jQuery(function() {if (jQuery("body.notebook_app").length == 0) { jQuery(".input_area").toggle(); jQuery(".prompt").toggle();}});</script>', raw=True)

# This line will add a button to toggle visibility of code blocks, for use with the HTML export version
di.display_html('''<button onclick="jQuery('.input_area').toggle(); jQuery('.prompt').toggle();">Toggle code</button>''', raw=True)


    

    












    





Toggle code

In [1]:

    

def count(f):
    def counted(n):
        counted.call_count += 1
        return f(n)
    counted.call_count = 0
    return counted


    

In [3]:

    

class Link:
    
    # __getitem__ is the built in Element selection []
    # __len__ Built-in len function
    
    empty = ()
    
    def __init__(self, first, rest=empty):
        self.first = first
        self.rest = rest
        
    def __getitem__(self, i): # This is recursive
        if i == 0:
            return self.first
        else:
            return self.rest[i-1]
        
    @count
    def __len__(self):
        return 1 + len(self.rest)
    
    # Right now if you call a Link class it gives you this built-in repr
    # string <__main__.Link instance at 0x104a693f8>
    # Let's improve on that
    def __repr__(self):
        if self.rest:
            rest_repr = ',' + repr(self.rest)
        else:
            rest_repr = ''
            
        return 'Link({0}{1})'.format(self.first, rest_repr)


    

In [4]:

    

s = Link(3, Link(4, Link(5)))


    

In [5]:

    

len(s)


    

    
Out[5]:





3

In [6]:

    

s[0]


    

    
Out[6]:





3

In [7]:

    

s.__len__.call_count # To see that len function for our linked list is indeed recursive.


    

    
Out[7]:





3

In [14]:

    

s


    

    
Out[14]:





Link(3,Link(4,Link(5)))

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