Loops and control transfers

while condition: repeats its suite while the Boolean condition is true. for name in source: evaluates its source and visits the supported sequence. Flat tuple unpacking is also accepted in the loop binding. Source kinds, iteration loans, generators, and comprehensions are described under iteration.

break exits the nearest loop. continue advances to its next iteration. Both must appear within a loop. Statements following either transfer are unreachable errors. Loops are unit-valued; loop else suites are unsupported.

Declarations inside a loop body do not establish values outside it. Assignments to existing mutable locals persist. A loop may run zero times and cannot alone prove that a function returns or that an initializer sets every field.

Control transfers destroy values whose ownership ends on that path. An explicit return exits the enclosing function, while ? follows the enclosing callable’s error propagation rule.