an item within the rowmatrix[ [ matrix[ ][ matrix[ ][ matrix [[ ][ ][ ]matrix[ ][ notice in the preceding interaction that lists can naturally span multiple lines if you want them to because they are contained by pair of bracketsthe " here are python' continuation line prompt (see for comparable code without the "sand watch for more on syntax in the next part of the bookfor more on matrixeswatch later in this for dictionary-based matrix representationwhich can be more efficient when matrixes are largely empty we'll also continue this thread in where we'll write additional matrix codeespecially with list comprehensions for high-powered numeric workthe numpy extension mentioned in and provides other ways to handle matrixes changing lists in place because lists are mutablethey support operations that change list object in place that isthe operations in this section all modify the list object directly--overwriting its former value--without requiring that you make new copyas you had to for strings because python deals only in object referencesthis distinction between changing an object in place and creating new object mattersas discussed in if you change an object in placeyou might impact more than one reference to it at the same time index and slice assignments when using listyou can change its contents by assigning to either particular item (offsetor an entire section (slice) ['spam''spam''spam!' [ 'eggsl ['spam''eggs''spam!' [ : ['eat''more' ['eat''more''spam!' lists and dictionaries index assignment slice assignmentdelete+insert replaces items ,