Generator
Iterable Objects
  1. #!/usr/bin/python
  2.  
  3. #list
  4. l = range(10);
  5. for i in l:
  6.     print i;
  7.  
  8. #tuple
  9. t = (1, 2, 3, 4);
  10. for i in t:
  11.     print i;
  12.  
  13. #dict
  14. d = {'x':1, 'y':2};
  15. for k in d:
  16.     print k;
  17.  
  18. #string
  19. s = 'Hello World!';
  20. for i in s:
  21.     print i;
  22.
Iterator
  1. #!/usr/bin/python
  2.  
  3. l = iter(range(10)); #iterator
  4.  
  5. try:
  6.     while True:
  7.         print l.next(); #if no more element, raise StopIteration
  8. except StopIteration:
  9.     pass
  10.
Implement Iterator as Classes
  1. #!/usr/bin/python
  2.  
  3. class yrange:
  4.     def __init__(self, n):
  5.         self.i = 0
  6.         self.n = n
  7.  
  8.     def __iter__(self): # make an object iterable
  9.         return self # return an iterator
  10.  
  11.     def next(self):
  12.         if self.i < self.n:
  13. 	              i = self.i
  14. 	              self.i += 1
  15. 	              return i
  16. 	          else:
  17. 	              raise StopIteration()
  18.  
  19. y = yrange(10);
  20.  
  21. l = list(y); # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  22. print l;
  23. l = list(y); # []
  24. print l;
  25. 		
  1. #!/usr/bin/python
  2.  
  3.  
  4. class zrange:
  5.     def __init__(self, n):
  6.         self.n = n
  7.  
  8.     def __iter__(self):
  9.         return zrange_iter(self.n)
  10.  
  11. class zrange_iter:
  12.     def __init__(self, n):
  13. 	          self.i = 0
  14. 	          self.n = n
  15.  
  16. 	      def __iter__(self):
  17. 	          # Iterators are iterables too.
  18. 	          # Adding this functions to make them so.
  19. 	          return self
  20.  
  21. 	      def next(self):
  22. 	          if self.i < self.n:
  23. 	              i = self.i
  24. 	              self.i += 1
  25. 	              return i
  26. 	          else:
  27. 	              raise StopIteration()
  28.  
  29. l = zrange(10);
  30.  
  31. print list(l); # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  32. print list(l); # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  33.
Generator
  1. #!/usr/bin/python
  2.  
  3. def yrange(n):
  4.     i = 0;
  5.     while i < n:
  6.     	yield i;
  7. 	i += 1;
  8.  
  9. l = yrange(10);
  10. for i in l:
  11. 	print i;
  12.  
  13. for i in l: # do not print anything, l has been consumed
  14. 	print i;
  15.
Generator Expression
  1. #!/usr/bin/python
  2.  
  3. # list
  4. l = [x*x for x in range(4)]; # [0, 1, 4, 9]
  5. print l;
  6.  
  7. # generator
  8. g = (x*x for x in range(4));
  9. for i in g:
  10. 	print i;
  11.
Reference