about performance laterafter your program is workingand after you've proved that there is genuine performance concern more often than notyour code will be quick enough as it is if you do need to tweak code for performancethoughpython includes tools to help you outincluding the time and timeit modules for timing the speed of alternativesand the profile module for isolating bottlenecks you'll find more on these later in this book (see especially ' benchmarking case studyand in the python manuals for the sake of this previewlet' move ahead to the next core data type tuples the tuple object (pronounced "toopleor "tuhple,depending on whom you askis roughly like list that cannot be changed--tuples are sequenceslike listsbut they are immutablelike strings functionallythey're used to represent fixed collections of itemsthe components of specific calendar datefor instance syntacticallythey are normally coded in parentheses instead of square bracketsand they support arbitrary typesarbitrary nestingand the usual sequence operationst ( len( -item tuple length > ( ( concatenation [ indexingslicingand more tuples also have type-specific callable methods as of python and but not nearly as many as listst index( count( tuple methods appears at offset appears once the primary distinction for tuples is that they cannot be changed once created that isthey are immutable sequences (one-item tuples like the one here require trailing comma) [ tuples are immutable error text omitted typeerror'tupleobject does not support item assignment ( , [ : ( make new tuple for new value tuples