line is executeda value is given to xbut is still undefined then gets value in line the comment on the right summarizes what is happening since has the value when line startsx+ is the same as + in line three we use the fact that the right side of an assignment statement uses the values of variables when the line starts executing (what is left after the previous line of the table executed)but the assignment to the variable on the left causes change to yand hence the updated value of is shown in the table line then changes xusing the latest value of ( not the initial value !the result from line confirms the values of and line comment = + using the value of from the previous line = * on the rightuse the value of from the previous line = - on the rightuse the value of and from the previous line print when we create such tablethe order of execution will always be the order of the lines in the table in this simple sequential codethat also follows the textual order of the program following each line of execution of program in the proper order of executioncarefullykeeping track of the current values of variableswill be called playing computer table like the one above is an organized way to keep track the list type lists are ordered sequences of arbitrary data lists are the first kind of data discussed so far that are mutablethe length of the sequence can be changed and elements substituted we will delay the discussion of changes to lists until further introduction to objects lists can be written explicitly read the following examples ['red''green''blue'[ ['silly' 'mixed'- 'example'[the empty list [ ][ ][list containing three elementseach list the basic format is square-bracket-enclosedcomma-separated list of arbitrary data the range functionpart there is built-in function rangethat can be used to automatically generate regular arithmetic sequences try the following in the shelllist(range( )list(range( )the general pattern for use is range(sizeofsequencethis syntax will generate the integersone at timeas needed if you want to see all the results at once as listyou can convert to list as in the examples above the resulting sequence starts at and ends before the parameter we will see there are good reasons to start from in python one important property of sequences generated by range(nis that the total number of elements is nthe sequence omits the number itselfbut includes instead with more parametersthe range function can be used to generate much wider variety of sequences the elaborations are discussed in random colors (page and the most general range function (page in computer jargonproducing values of sequence only as needed is called lazy evaluation beginning with python