Python - Membership: __contains__, __iter__, and __getitem__

Description

Membership: __contains__, __iter__, and __getitem__

Demo

from __future__ import print_function         # 2.X/3.X compatibility 
# w w  w  .j a  va 2  s.co m
class Iters: 
   def __init__(self, value): 
       self.data = value 
    
   def __getitem__(self, i):                 # Fallback for iteration 
       print('get[%s]:' % i, end='')         # Also for index, slice 
       return self.data[i] 
    
   def __iter__(self):                       # Preferred for iteration 
       print('iter=> ', end='')              # Allows only one active iterator 
       self.ix = 0 
       return self 
    
   def __next__(self): 
       print('next:', end='') 
       if self.ix == len(self.data): raise StopIteration 
       item = self.data[self.ix] 
       self.ix += 1 
       return item 
    
   def __contains__(self, x):                # Preferred for 'in' 
       print('contains: ', end='') 
       return x in self.data 
   next = __next__                           # 2.X/3.X compatibility 

if __name__ == '__main__': 
   X = Iters([1, 2, 3, 4, 5])        # Make instance 
   print(3 in X)                     # Membership 
   for i in X:                       # for loops 
       print(i, end=' | ') 

   print() 
   print([i ** 2 for i in X])        # Other iteration contexts 
   print( list(map(bin, X)) ) 

   I = iter(X)                       # Manual iteration (what other contexts do) 
   while True: 
       try: 
           print(next(I), end=' @ ') 
       except StopIteration: 
           break

Result

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