Seite - 63 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Band Second Edition

3.1 TheforLoop 63 Running ThroughCode“byHand” It is appropriate to stress that much understanding is often developedby first goingthroughcode“byhand”, i.e. just read thecodewhiledoingcalculations byhand,beforecomparingthesehandcalculations towhat thecodeproduces whenrun (oftensome print commandsmust be inserted in thecode toenable detailedcomparison). Thus,tomakesureyouunderstandtheimportantdetails inaverage_height. py, youare encouraged to go through that code byhandright now.Also, in a copy, insert a print commandin the loop, so that you can compare the output fromthatprogramtoyourowncalculations, iterationby iteration. 3.1.4 UsingtherangeFunction At this point, the observant reader might argue: “Well, thisfor loop seems handy, butwhat if the loopmustdoa really largenumberof iterations? If the loopvariable is to runthroughhundredsofnumbers,wemustspendallday typingthosenumbers into the loopheader”! An Example This is where the built-in range function enters the picture. When called, therangefunctionwillprovideintegersaccordingto theargumentsgivenin thefunctioncall.Forexample,wecouldhaveusedrange inaverage_height.py by just changingtheheader from for i in [0, 1, 2, 3, 4]: # original code line to for i in range(0, 5, 1): # new code line Here, range(0, 5, 1) is a function call, where the function range is told to provide the integers from 0 (inclusive) to 5 (exclusive!) in steps of 1. In this case, range(0, 5, 1)will provide exactly those numbers that we had in the original code, i.e., the loop variableiwill run through the same values (0, 1, 2, 3 and 4) as before,andprogramcomputationsstay the same. Withalittle interactivetest,wemayconfirmthattherangefunctionprovidesthe promised numbers.However, since what is returned from therange function is an object of typerange, the number sequence is not explicitly available.4 Converting the rangeobject toa list, however,does the trick. In [1]: x = range(0, 5, 1) In [2]: type(x) Out[2]: range In [3]: x Out[3]: range(0, 5) 4 In Python 2, therange function returned the requested numbers asa list.