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Iterator

Inside each iterable class, the _ _ iter__ () method is implemented, which returns an iterative class object, which defines how the iterable class iterates.

The for loop invokes list essentially by calling list's iterator for iteration.

# the for loop on list is essentially a call to the iterator list of list = [1 for 2, 3, 4] # for loop calls for elem in list: print (elem) # iterator calls list_iter = list.__iter__ () while True: try: print (next (list_iter)) except StopIteration: break

Implement a self-defined iteration class that specifies a "countdown" mode to iterate over an iterable data structure.

# iterative object class class CountDown (object): def _ _ init__ (self,num): self.num = num def _ iter__ (self): return MyIterator (self.num) # iterative class class MyIterator (object): def _ init__ (self) Num): self.NUM= num self.FINAL = 0 self.now = num def _ _ iter__ (self): return self def _ _ next__ (self): step = 1 if self.NUM

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