4.1 VariablesVariables can be assigned to hold numerical values using syntax of the form a = 5.2 * sqrt(64) which may optionally be written in longhand as let a = 5.2 * sqrt(64) Variables can subsequently be used by name in mathematical expressions, for example: print a / sqrt(64) Having been defined, variables can later be undefined – set to have no value – using syntax of the form: a = Variables can also hold nonnumeric data, such as strings, colors, dates, lists and dictionaries. The syntax for defining many of these data structures is similar to that used by python, for example: myList = [8,2,1,7] myDict = {'john':27 , 'fred':14 , 'lisa':myList} myDate = time.fromCalendar(2012,7,1,14,30,0) More information about Pyxplot’s data types can be found in Chapter 6. A list of all of the variables which are currently defined can be obtained by typing show variables. Some constants are predefined by Pyxplot, and so a number of variables are listed even if none have been set by the user.
