variablesexpressionsand statements int(speed int(speed but if the user types something other than string of digitsyou get an errorspeed input(promptwhat is the airspeed velocity of an unladen swallowwhat do you meanan african or european swallowint(speedvalueerrorinvalid literal for int(with base we will see how to handle this kind of error later comments as programs get bigger and more complicatedthey get more difficult to read formal languages are denseand it is often difficult to look at piece of code and figure out what it is doingor why for this reasonit is good idea to add notes to your programs to explain in natural language what the program is doing these notes are called commentsand in python they start with the symbolcompute the percentage of the hour that has elapsed percentage (minute in this casethe comment appears on line by itself you can also put comments at the end of linepercentage (minute percentage of an hour everything from the to the end of the line is ignoredit has no effect on the program comments are most useful when they document non-obvious features of the code it is reasonable to assume that the reader can figure out what the code doesit is much more useful to explain why this comment is redundant with the code and uselessv assign to this comment contains useful information that is not in the codev velocity in meters/second good variable names can reduce the need for commentsbut long names can make complex expressions hard to readso there is trade-off