Nested Loops in Python: Use Cases and Considerations

Nested loops in Python are an advanced technique for handling multi - level repetitive tasks, referring to the situation where one loop is contained within another. The outer loop controls the overall scope, while the inner loop deals with the details. Its core scenarios include: 1. **Traversal of 2D data**: For example, a student grade sheet (a list of lists), where the outer loop iterates over students and the inner loop accumulates grades. 2. **Graph generation**: Printing regular graphs through nested loops, such as right - angled triangles (the outer loop controls the number of rows, and the inner loop controls the number of stars in each row) and rectangles. 3. **List combination**: Achieving full pairing of elements from multiple lists (Cartesian product), such as all element combinations of two lists. When using nested loops, the following points should be noted: Avoid having more than 3 levels of nesting (to reduce readability); ensure that loop variable names do not conflict; optimize performance when the data volume is large (such as using list comprehensions instead of simple nested loops); strictly indent the code; and clearly understand the scope of the break/continue statements (they only terminate the current inner loop). Reasonable use of nested loops can efficiently solve complex repetitive problems. However, it is necessary to balance readability and performance, and gradually master it by practicing basic scenarios such as the multiplication table.