Page - 70 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Volume Second Edition

70 3 LoopsandBranching out with the simplest version of the code, complexity is added step by step, before arrivingat thefinalversion.Ateachstep,youmakesure thecodeworksasplanned. Such a procedure is generally a good idea, and we will address it explicitly again, whenwe programa(slightly)morecomprehensivecase inSect.4.2. 3.3.2 TheCharacteristicsofBranching Amoregeneral formofanif-elif-elseconstructionreads if condition_1: # testing condition 1 <code line 1> <code line 2> ... elif condition_2: # testing condition 2 <code line 1> <code line 2> ... elif condition_3: # testing condition 3 <code line 1> <code line 2> ... else: <code line 1> <code line 2> ... # First line after if-elif-else construction Here we see an if part, two elif parts and an else part. Note the compulsory colon and indented code lines (a block of statements) in each case. As with loops, indents are conventionally 4 spaces. In such an arrangement, there may be “any” numberofelifparts (alsonone)and theelsepartmay,ormaynot,bepresent. When interpreting an arrangement like this, Python starts checking the condi- tions, one after the other, from the top. If a condition (here, eithercondition_1, condition_2or condition_3) evaluates to True, the corresponding code lines areexecuted,beforeproceedingdirectly to thefirst lineafter thewholearrangement (here, to the line # First line after if-elif-else construction). This means that any remaining tests, and theelsepart, are simply skipped! If none of theconditionsevaluate toTrue, theelsepart (whenpresent) is executed. 3.3.3 Example:FindingtheMaximumHeight We have previously modified ball_plot.py from Sect.1.5 to find the time of flight instead(seeball_time.py).Letusnowchangeball_plot.py inaslightly differentway, so that the new programinstead finds the maximum height achieved by the ball.