Seite - 8 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Band Second Edition

8 1 TheFirstFewSteps This is a print function call, which makes Python print the value of y on the screen.4 Simply stated, the value ofy is sent to a ready-madepiece of code named print (being a function—see Chap.4, here called with a single argument named y), which then takes care of the printing. Thus, whenball.py is run, the number 1.2342appearson thescreen. Readabilityand Coding Style In the codeabove,yousee several blank lines too. ThesearesimplyskippedbyPythonandyoumayuseasmanyasyouwanttomakea niceandreadablelayoutofthecode.Similarly,younoticethatspacesareintroduced to each side of− in the “formula” and to each side of= in the assignments. These spaces are not required, i.e., Python will understand perfectly well without them. However, they contribute to readability and it is recommended to use them5 as part of good coding style.6 Had there been a+ sign in there, it too should have a space toeachside.To the contrary,noextra spacesare recommendedfor/,*and**. SeveralStatementsonOneLine Note that it’sallowed tohaveseveral statements on the same line if they are separated by a semi-colon. So, with our program here, wecouldhavewritten, e.g., # Program for computing the height of a ball in vertical motion # v0 is the intial velocity, g is the acceleration of gravity, t is time v0 = 5; g = 9.81; t = 0.6 y = v0*t - 0.5*g*t**2 # vertical position print(y) Ingeneral,however, readability is easilydegradedthisway,e.g.,makingcomment- ingmoredifficult, so it shouldbedonewithcare. Assignments like a=2*a Frequently,you will meet assignment statements in which the variable name on the left hand side (of=) also appears in the expression on the right hand side. Take, e.g., a = 2*a. Python would then, according to its rules, first compute the expression on the right hand side with the current value of a and then let the result become the updatedvalue ofa through the assignment (theupdatedvalueofa isplaced in anew“box” in computermemory). 4 In Python 2.7, thiswould have been a print command readingprint y. 5 Beaware that incertainsituationsprogrammersdoskipsuchspaces, e.g.,whenlistingarguments in function calls, asyou will learn more about inChap.4. 6 You might like to check out the style guide for Python coding at https://www.python.org/dev/ peps/pep-0008/.