Class LazyZip

source code

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

Known Subclasses:

• LazyEnumerate

A lazy sequence whose elements are tuples, each containing the i-th element from each of the argument sequences. The returned list is truncated in length to the length of the shortest argument sequence. The tuples are constructed lazily -- i.e., when you read a value from the list, LazyZip will calculate that value by forming a tuple from the i-th element of each of the argument sequences.

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

>>> zip(sequences...)
>>> list(LazyZip(sequences...))

Lazy zips 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 combining long sequences of gold standard and predicted values in a classification or tagging task in order to calculate accuracy. By constructing tuples lazily and avoiding the creation of an additional long sequence, memory usage can be significantly reduced.