introduction to python perhaps we shouldn' have said" variable is just name despite what juliet said names matter programming languages let us describe computations in way that allows machines to execute them this does not mean that only computers read programs as you will soon discoverit' not always easy to write programs that work correctly experienced programmers will confirm that they spend great deal of time reading programs in an attempt to understand why they behave as they do it is therefore of critical importance to write programs in such way that they are easy to read apt choice of variable names plays an important role in enhancing readability consider the two code fragments *( ** pi diameter area pi*(diameter** as far as python is concernedthey are not different when executedthey will do the same thing to human readerhoweverthey are quite different when we read the fragment on the leftthere is no priori reason to suspect that anything is amiss howevera quick glance at the code on the right should prompt us to be suspicious that something is wrong either the variable should have been named radius rather than diameteror diameter should have been divided by in the calculation of the area in pythonvariable names can contain uppercase and lowercase lettersdigits (but they cannot start with digit)and the special character python variable names are case-sensitive julie and julie are different names finallythere are small number of reserved words (sometimes called keywordsin python that have built-in meanings and cannot be used as variable names different versions of python have slightly different lists of reserved words the reserved words in python are andasassertbreakclasscontinuedefdelelifelseexceptexecfinallyforfromglobalifimportinislambdanotorpassprintraisereturntrywithwhileand yield another good way to enhance the readability of code is to add comments text following the symbol is not interpreted by python for exampleone might write #subtract area of square from area of circle areac pi*radius** areas side*side difference areac-areas python allows multiple assignment the statement xy binds to and to all of the expressions on the right-hand side of the assignment are evaluated before any bindings are changed this is convenient "what' in namethat which we call rose by any other name would smell as sweet