the interpreter runs statements until it reaches the end of the input file if it' running interactivelyyou can exit the interpreter by typing the eof (end of filecharacter or by selecting exit from pull-down menu of python ide on unixeof is ctrl+don windowsit' ctrl+ program can request to exit by raising the systemexit exception raise systemexit variables and arithmetic expressions the program in listing shows the use of variables and expressions by performing simple compound-interest calculation listing simple compound-interest calculation principal initial amount rate interest rate numyears number of years year while year <numyearsprincipal principal ( rateprint yearprincipal reminderprint(yearprincipalin python year + the output of this program is the following table python is dynamically typed language where variable names are bound to different valuespossibly of varying typesduring program execution the assignment operator simply creates an association between name and value although each value has an associated type such as an integer or stringvariable names are untyped and can be made to refer to any type of data during execution this is different from cfor examplein which name represents fixed typesizeand location in memory into which value is stored the dynamic behavior of python can be seen in listing with the principal variable initiallyit' assigned to an integer value howeverlater in the program it' reassigned as followsprincipal principal ( ratethis statement evaluates the expression and reassociates the name principal with the result although the original value of principal was an integer the new value is now floating-point number (rate is defined as floatso the value of the above expression is also floatthusthe apparent "typeof principal dynamically changes from an integer to float in the middle of the program howeverto be preciseit' not the type of principal that has changedbut rather the value to which the principal name refers newline terminates each statement howeveryou can use semicolon to separate statements on the same lineas shown hereprincipal rate numyears lib fl ff