Processing sequences efficiently.
WHAT AN ITERATOR IS
Something producing values one at a time, on request.
WHY THAT MATTERS
The whole sequence need not exist in memory.
WHAT A GENERATOR IS
A function producing values lazily, resuming where it left off.
WHAT LAZY EVALUATION MEANS
Work performed only when the result is needed.
WHAT IT ENABLES
Processing sequences larger than memory Infinite sequences Avoiding computing values never used
WHAT THAT LOOKS LIKE PRACTICALLY
Reading a very large file line by line rather than loading it entirely.
WHY THAT MATTERS
Loading a large file entirely exhausts memory, and the failure appears only with real data.
WHAT TO BE CAREFUL WITH
Iterators that can be consumed only once Lazy sequences where the underlying source has closed Chained operations obscuring how much work occurs
THAT SECOND POINT
A common error: returning a lazy sequence from a function that closes the file.
WHAT TO DO ABOUT IT
Materialise it before the source closes, or keep the source open.
WHAT TO PREFER FOR LARGE DATA
Streaming, always.
