Control flow

Ensures early exit from nested loops when a condition is met, otherwise executes a fallback action.

Grid search: stop scanning when the product of indices exceeds a threshold Matrix traversal: exit both loops immediately after finding a target cell

Algorithm implementations, search problems, combinatorial generation scripts, educational examples of loop control.

for outer_var in range(outer_limit): for inner_var in range(inner_limit): if condition(outer_var, inner_var): break else: continue break else: fallback_action()

for ... in ...: for ... in ...: if ...: break else: continue break else: ...

outer_var: int, outer_limit: int ≥ 0, inner_var: int, inner_limit: int ≥ 0, condition: callable[[int, int], bool], fallback_action: callable or statement

• break
• continue
• for-else
• nested loops
• early exit
• fallback action

• Use a flag variable to track condition instead of for-else – clearer to readers unfamiliar with for-else Replace nested loops with a generator expression and any() – more concise for simple predicates Use itertools.product with a break flag – reduces manual nesting

Placing the break in the outer loop instead of the inner one, causing premature termination of the entire search Assuming the else clause belongs to the outer loop, leading to the fallback never executing Forgetting the else clause entirely, so the fallback action is omitted when no break occurs Using mutable default arguments in the condition function, resulting in unexpected state across iterations Confusing continue with break inside the inner loop, altering the intended control flow

while-else pattern – similar semantics but with while loops Flag-variable approach – achieves the same early exit without for-else syntax

Coming from C: expecting an else clause after a for loop → Python's for-else executes only when the loop completes without a break

• loop_control
• early_exit
• for_else
• nested_loops

Do not use this pattern when the loop body is complex; a flag variable may be clearer The additional else and continue clauses add negligible runtime overhead but can impact readability The outer else runs only if the outer loop finishes without encountering a break; nested else applies to the inner loop only

Provides a compact way to exit nested loops early and handle the no‑match case without extra flag variables, reducing boilerplate and potential bugs.

Think of the nested loops as a search party: they keep looking until someone finds the treasure (break); if nobody finds it, they report back (else).

The outer break after the inner else ensures that once the inner loop breaks, the outer loop also terminates, mimicking a double break.

Replace the nested loops with a generator expression and any() for concise condition checking.