Journey

Iteration

This journey follows repeated work from ordinary loops to the iterator protocol: consume values, stop deliberately, and produce lazy streams only when they help.

In this journey

Choose the right loop shape.
See the protocol behind `for`.
Compose lazy value streams.

Choose the right loop shape.

Loops differ by what they consume, when they stop, and whether completion itself carries meaning.

Choose the loop from its stopping rule: exhaustion, condition, or sentinel marker.

For Loops
Use this example to consume values from an iterable.
While Loops
Use this example to repeat while a condition must be rechecked.
Break and Continue
Use this example to interrupt or skip loop work intentionally.
Loop Else
Use this example to attach completion logic to loops that did not break.
Sentinel Iteration
Use this example to show `iter(callable, sentinel)` for repeated reads until a marker appears.

See the protocol behind `for`.

The important mental shift is that loops consume producers through a protocol rather than special-casing lists.

for is surface syntax; iter() creates an iterator and next() pulls values until StopIteration.

Iterating over Iterables
Use this example to separate value producers from value consumers.
Iterators
Use this example to use `iter()` and `next()` to expose the protocol behind `for`.
Generators
Use this example to write functions that produce values lazily.

Compose lazy value streams.

Iterator pipelines are useful when code can transform values one at a time instead of materializing every intermediate result.

Lazy pipelines run from the consumer's pull: next() requests one value through each stage.

Generator Expressions
Use this example to create lazy one-pass streams with expression syntax.
Itertools
Use this example to compose iterator streams without materializing every value.
Yield From
Use this example to delegate part of a generator to another iterable.