Worked Exercise- 2.3

Hello, and welcome to Python for Everybody, my name’s Charles Severance. In this short video, I will be explaining how to run exercise 2.3 where we prompt for some hours, prompt for some rates, and multiply them together, and print them out with a little pay message. And so, this is 2.3, some of you will immediately want to go to the autograder, and sort of do your homework in the autograder. I really rather you didn’t do that, unless of course you’re doing this on an iPad, or an Android, or something where you can’t install Python, but you have to realize that the autograder isn’t forever. You can only go so far with the autograder, and eventually, you have to write a real Python program. So, I’ll eventually show you how to run this autograder, but I’m going to instead show you how to run it in the terminal. So, I’m first going to go into my Python for Everybody folder, and I’m going to make a new folder, command Shift+N is what I just did there, ex 02 03, for Exercise 3, so there’s exercise 3. And I’m also going to go into Atom, which is my text editor, and see I have that folder. And so, I’m going to make a new file, and I will say print, I’ll just say PY4E, oops, PY4E, and then I will say File, Save As, and I want to make sure it’s in here, and it’s going to be ex 02. I don’t like putting spaces in file names, some operating systems can’t handle them, that’s why I’m using underscores here, so I would avoid using spaces in file names. So as soon as I give that a PY4E, as soon as I give it a python suffix I’m there, and so it shows up there in my desktop, and now I’m going to run the terminal program, so that I can get there. So, cd Desktop/ cd py4e/ That’s the folder on my desktop, If I do an ls I see a couple folders and a file, you can say ls -l and see a little more detail that these are folders, these two are folders, and this one’s a file. So change directory cd ex 02 03, and so now I’m in that folder, and if I do an ls -l, I see that file. I can also do an ls without the -l, and see the file. And now I say python3 ex 02 03.py, and it runs. And you’ll see me, no matter how many times you watch me, you’ll see that the first thing that I do, is get to the point where I know I’m in the right directory, and I can run a little hello program, before I start coding. I just don’t like being crazy, right? So now, I’m going to go back and take a look at my assignment, Enter Hours, you’ve got a prompt for hours, ask for a number, Enter Rate, prompt for rate, and then calculate Pay. So, there’s a couple of input statements here, xh is my variable I’m going to choose, later I’ll choose more effective variables, but for now I’m going to make them silly, Enter Hours, colon, space. And then I’m going to copy, and paste and call this xr for rate. When you’re doing this, you need to be very careful to, and so now I’m going to calculate xp times, which is xh xr, and I’ll say print Pay. I don’t need to put a space because this comma effectively creates a space, xp. And then I want to save that, and I’m going to switch to my terminal program, clear my screen in my terminal program, and I’m going type up arrow, because I already typed python3 ex 02 03.py. So my hours, I’ll just start with something really simple that I can calculate in my head, 10 and 5. Whoops, can’t multiply sequence of non-int of, by sequence of non-int of type str. Here we have a traceback, and again I encourage you to realize that these tracebacks are not personal attacks by Python on you, even though they might be frustrating. And so the way to parse this is start by saying line 3, something’s wrong at line 3, it’s pretty good at knowing what line it is, or it’s either that line or the line above it, and it’s something about multiplying. What it’s really saying is I’m confused, I have to stop because I cannot understand your instructions. So, the problem here of course is that this is of type string. And so you can’t multiply a string times a string. Okay, and so we can convert this using a float, float, so that’s a function call now, we’re passing the string xh in, and the value we get back is the floating point version of that, and then, we call float for this as well. And so now I’ll save that, always remember to save. I’m going to run it, and so I’m going to run it my hours of 10, and my rate of 10, and it’s 100, and so that looks pretty good, okay? So let’s go ahead and try to run this in the autograder, and this is my idea, is you’ll take this and you’ll copy it, and you’ll go back to the autograder now, and just paste this in, okay? And so it says use 35 hours, and rate of 2.75, so let’s check the code 35 hours, OK, 75, no 2.75. And so it’s running, and it’s running, and it works, and of course, now I’ve got my grade. So this idea where you work here to get your assignment done correctly, and then you run it in the autograder, is the way I intend for you to do it, but again if you can’t do it that way, it’s a great way to get started to just write your code it the autograder. You can change your code in the autograder, and then run it again. Of course, this is going to fail, 35, and 2.75. And of course you get a mismatch, and now it’s angry at you, and the mismatch here, of course, is because I print Howdy Pay and Pay, and it’s real picky about it, and you think I’ve got the 96.25 right. Well, it doesn’t really care so much about that. So, let me go ahead and fix this, and run it so we leave on a successful note 35 hours, and 2.75 is the rate per hour, kind of a lower rate per hour, and we’re getting successful. And of course that means that you now have a grade on assignment 2.3, look at that, I got a grade on assignment 2.3, unless of course, you’re running these in some other environment, okay? Thank you so much, and I hope that this has been useful to you.