Class LazyEnumerate

source code

          object --+            
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AbstractLazySequence --+        
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                 LazyMap --+    
                           |    
                     LazyZip --+
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                              LazyEnumerate

A lazy sequence whose elements are tuples, each ontaining a count (from zero) and a value yielded by underlying sequence. LazyEnumerate is useful for obtaining an indexed list. The tuples are constructed lazily -- i.e., when you read a value from the list, LazyEnumerate will calculate that value by forming a tuple from the count of the i-th element and the i-th element of the underlying sequence.

LazyEnumerate is essentially a lazy version of the Python primitive function enumerate. In particular, the following two expressions are equivalent:

>>> enumerate(sequence)
>>> list(LazyEnumerate(sequence))

Lazy enumerations can be useful for conserving memory in cases where the argument sequences are particularly long.

A typical example of a use case for this class is obtaining an indexed list for a long sequence of values. By constructing tuples lazily and avoiding the creation of an additional long sequence, memory usage can be significantly reduced.