Python: The Iterator Pattern

Python: The Iterator Pattern

• 1.
  Iterator Pattern Damian Gordon
• 2.
  Iterator Pattern • Theiterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.
• 3.
  Iterator Pattern • Theiterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.
• 4.
  Iterator Pattern • Theiterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.
• 5.
  Iterator Pattern • Theiterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.
• 6.
  Iterator Pattern • Theiterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.
• 7.
  Iterator Pattern • Theiterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.
• 8.
  Iterator Pattern • Theiterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.
• 9.
  Iterator Pattern • Theiterator pattern is a design pattern in which an iterator is used to traverse a container and access the container's elements.
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  Iterator Pattern • Ina programming language without patterns, an iterator would have a next() method and a done() method, and the iterator loops across all the containers using these methods.
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  Iterator Pattern • Ina programming language without patterns, an iterator would have a next() method and a done() method, and the iterator loops across all the containers using these methods. WHILE NOT(iterator.done()) DO item = iterator.next() # do more stuff ENDWHILE;
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  Iterator Pattern • Theiterator pattern in Python has the following features: Name Description _ _next_ _() The next method returns the next element from the container. StopIteration() The StopIteration is an exception that is raised when the last element is reached. _ _iter_ _() The iter method makes the object iterable, and returns an iterator.
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  Iterator Pattern • Theiterator pattern has two parts: –An iterable class (to create the iterator object) –An iterator class (to traverse a container)
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  def __init__(self, VALUE): self.VALUE= VALUE # END Init def __iter__(self): return ITERATOR(self.VALUE) # END Iter class ITERABLE: # END ITERABLE.
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  def __init__(self, VALUE): self.VALUE= VALUE self.index = 0 # END Init def __iter__(self): return self # END Iter def __next__(self): if CONDITION: VALUE = SELF.VALUE self.index = self.index + 1 return VALUE else: raise StopIteration() # ENDIF; # END Next class ITERATOR: # END ITERATOR.
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  Iterator Pattern • Let’slook at a simple example that counts numbers, there’ll be three parts: – The Iterable part – The Iteration part – The program execution part
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  Iterator Pattern class MyCountIterable: def__init__(self, Value): self.Value = Value # END Init def __iter__(self): return MyCountIteration(self.Value) # END Iter # END MyCountIterable.
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  Iterator Pattern class MyCountIteration: def__init__(self, Value): self.Index = 0 self.Value = Value # END Init def __iter__(self): # Iterators are iterables too. return self # END Iter def __next__(self): if self.Index < self.Value: # THEN Index = self.Index self.Index += 1 return Index else: raise StopIteration() # ENDIF; # END Next # END MyCountIteration.
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  Iterator Pattern FirstCount =MyCountIterable(5) list(FirstCount) FirstCountIter = iter(FirstCount) while True: # DO try: print(next(FirstCountIter)) except StopIteration: break # ENDWHILE
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  Iterator Pattern FirstCount =MyCountIterable(5) list(FirstCount) FirstCountIter = iter(FirstCount) while True: # DO try: print(next(FirstCountIter)) except StopIteration: break # ENDWHILE 0 1 2 3 4
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  Iterator Pattern • Hangon… • Couldn’t we just do: • YES! for Counter in range(0,5): print(Counter) # ENDFOR;
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  etc.