sometimes you would like to repeat command you have given earlieror perhaps give command that is almost the same as an earlier one then you can use the up-arrow key pressing this one time gives you the previous commandpressing two times gives you the command before thatand so on with the down-arrow key you can go forward again when you have the relevant command at the promptyou may edit it before pressing enter (which lets python read it and take actionarithmeticsparentheses and rounding errors when the arithmetic operators +-*and *appear in an expressionpython gives them certain precedence python interprets the expression from left to righttaking one term (part of expression between two successive or -at time within each term*is done before and consider the expression * ** * there are three terms here and interpreting thispython starts from the left in the first term * ** it first does ** which equals this is then multiplied by to give again the second term is * so the first two terms add up to the last term gives so the final result is which becomes the value of note that parentheses are often very important to group parts of expressions together in the intended way let us say and that you want to divide by we know the answer is but the way we present the task to python is criticalas shown by the following example in [ ] in [ ] / + out [ ] in [ ] /( + out [ ] in the first trywe see that is divided by ( )giving which is then added to python did not understand that our complete denominator was + in our second trywe used parentheses to "groupthe denominatorand we got what we wanted that isalmost what we wantedsince most numbers can be represented only approximately on the computerthis gives rise to what is called rounding errors we should have got as our answerbut the inexact number representation gave small error usuallysuch errors are so small compared to the other numbers of the calculationthat we do not need to bother with them stillkeep it in mindsince you will encounter this issue from time to time more details regarding number representations on computer is given in section variables and objects variables in python will be of certain type if you have an integersay you have written in some python programthen becomes an integer variablei variable of type int similarlywith the statement becomes float