Page - 88 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Volume Second Edition

88 4 FunctionsandtheWritingofCode Remember that only one of the branches is executed for a single call to check_sign, so depending on the number x, the return may take place from anyof the three returnalternatives. To Returnat theEnd or Not Programmers disagree whether it is a good idea to use return inside a function, or if there should be just a single return statement at the end of the function.Theauthorsof thisbookemphasize readablecodeand think that returncan be useful in branchesas in the exampleabovewhen the function is short. For longer or more complicated functions, it might be better to have onesinglereturn statementat theend. NestedFunctions Functions may also be defined within other functions. In that case, they become localfunctions,ornestedfunctions,knownonlytothefunctioninside which theyaredefined. Functions defined in main are referred to as global functions. A nested functionhasfullaccess toallvariables in theparent function, i.e. the function withinwhich it isdefined. OverheadofFunctionCalls Function calls have the downside of slowing down program execution. Usually, it is a good thing to split a program into functions, but in very computing intensive parts, e.g., inside long loops, one must balance the convenienceofcallingafunctionandthecomputationalefficiencyofavoiding functioncalls. It isagoodrule todevelopaprogramusingplentyof functions and then in a later optimization stage, when everything computes correctly, removefunctioncalls thatarequantifiedtoslowdownthecode.Let itbeclear, however, that newcomers to programming should focus on writing readable code,not fast code! In Sect.5.6, we investigate (for a particular case) the impact that function callshaveonCPU time. 4.2 ProgrammingasaStep-WiseStrategy When students start out with programming, they usually pick up the basic ideas quite fast and learn to read simpler code rather swiftly. However,when it comes to thewritingofcode,manyfind ithard toevenget started.