1
00:00:00,150 --> 00:00:00,540
Now,

2
00:00:00,540 --> 00:00:05,540
there are so many possible solutions to create this coffee machine program

3
00:00:05,760 --> 00:00:10,760
satisfying all the requirements. And the way that you code it up is essentially

4
00:00:12,000 --> 00:00:13,080
your choice, right?

5
00:00:13,440 --> 00:00:17,970
Whether if you decide to use a while loop or use a for loop or create a

6
00:00:17,970 --> 00:00:21,540
different data structure, there are endless possibilities.

7
00:00:21,840 --> 00:00:25,320
What I'm going to show you now is just one of those possibilities.

8
00:00:25,890 --> 00:00:29,790
And what's really important is you don't feel like you've done it wrong

9
00:00:29,790 --> 00:00:33,120
just because it's different to mine. As long as it works

10
00:00:33,120 --> 00:00:36,900
the way that you expect it to, then consider yourself successful.

11
00:00:37,650 --> 00:00:41,520
The first thing I'm going to do is create a new project in PyCharm,

12
00:00:41,910 --> 00:00:46,740
and I'm going to call my project coffee machine. Again,

13
00:00:46,770 --> 00:00:51,570
making sure that I've got the latest version of Python as the interpreter I'll

14
00:00:51,570 --> 00:00:52,403
click

15
00:00:52,490 --> 00:00:53,323
create.

16
00:00:54,860 --> 00:00:58,700
Now that the first thing I'm going to do here is right-click on this and create

17
00:00:58,730 --> 00:01:02,210
a new file, which is going to be my main.py.

18
00:01:02,810 --> 00:01:07,160
And then I'm going to go to my starting project in Repl.it and I'm just going to

19
00:01:07,160 --> 00:01:12,160
copy everything there is over here and paste it into this main.py.

20
00:01:13,370 --> 00:01:18,370
Now you might find the font of your code or of PyCharm a little bit too big or

21
00:01:19,190 --> 00:01:21,350
too small. If that's the case,

22
00:01:21,350 --> 00:01:26,350
you can just go into preferences and change the appearance and the font to a

23
00:01:27,830 --> 00:01:30,680
different size. And this is for the user interface.

24
00:01:31,130 --> 00:01:35,210
And if you want to change the font of the editor, then you can go here,

25
00:01:35,270 --> 00:01:38,120
go to font and then change that size here.

26
00:01:38,600 --> 00:01:41,810
I've tried to make it as large as possible so that when you were looking at this

27
00:01:41,810 --> 00:01:46,100
video on an iPad or an iPhone, all the code still be readable.

28
00:01:46,460 --> 00:01:48,230
But of course, normally when you're coding,

29
00:01:48,230 --> 00:01:52,250
you'd probably want to fit more lines into the same screen,

30
00:01:52,730 --> 00:01:56,300
but it's not good to strain your eyes. So try to strike a balance there.

31
00:01:57,110 --> 00:02:00,800
Now I'm going to collapse that sidebar because I'm going to be coding entirely

32
00:02:00,800 --> 00:02:01,880
in this one file.

33
00:02:02,510 --> 00:02:06,080
Now notice that the beginning we get given a menu,

34
00:02:07,070 --> 00:02:11,210
and this is a dictionary which contains three entries.

35
00:02:11,690 --> 00:02:15,050
And each of those entries have a name of a drink,

36
00:02:15,140 --> 00:02:16,820
espresso, latte and cappuccino.

37
00:02:17,210 --> 00:02:21,140
And then each of them have a value that holds a bunch of data,

38
00:02:21,500 --> 00:02:24,650
including the ingredients that are required to make that drink

39
00:02:24,980 --> 00:02:29,840
and also the price of the drink. Now there's also a resources dictionary,

40
00:02:29,870 --> 00:02:32,900
which holds the resources of the coffee machine.

41
00:02:33,740 --> 00:02:36,440
Now that we've got all of that, then we're ready to go.

42
00:02:37,070 --> 00:02:39,740
I'm going to tackle these requirements one by one.

43
00:02:40,370 --> 00:02:43,670
And the first one says to prompt the user by asking,

44
00:02:43,700 --> 00:02:46,880
what would you like? Espresso, latte or cappuccino.

45
00:02:46,880 --> 00:02:51,880
So I'm actually gonna just straight up copy this line and put that into an

46
00:02:51,950 --> 00:02:55,730
input. This is going to be saved into some sort of variable,

47
00:02:55,730 --> 00:02:57,140
which I'll name choice.

48
00:02:58,550 --> 00:03:03,010
Now it tells me that the prompt should show every time action has completed.

49
00:03:03,280 --> 00:03:03,820
For example,

50
00:03:03,820 --> 00:03:07,660
once the drink is dispensed and it should show again and again and again.

51
00:03:07,930 --> 00:03:11,970
So that means we probably going to have to embed this input in some sort of while

52
00:03:11,970 --> 00:03:16,270
loop. So I'm just gonna say for now while something is true,

53
00:03:16,570 --> 00:03:20,110
then keep asking for this prompt. Right now

54
00:03:20,140 --> 00:03:25,140
if we decide to go and run this code where we go to run and then click on this

55
00:03:25,540 --> 00:03:29,140
button and then select the main.py to run,

56
00:03:29,800 --> 00:03:33,790
then you can see that it asks me what would you like? And if I've put an input,

57
00:03:33,880 --> 00:03:36,910
it'll keep asking me until eternity, basically,

58
00:03:36,910 --> 00:03:40,870
because that there's currently no way of turning that true into a false.

59
00:03:41,740 --> 00:03:43,720
So let's take a look at the next requirement.

60
00:03:43,900 --> 00:03:48,010
We should be able to turn off the coffee machine by entering off into the prompt.

61
00:03:48,610 --> 00:03:50,290
For maintainers of the coffee machine,

62
00:03:50,290 --> 00:03:54,160
they can use off as the secret word to turn off the machine and your code should

63
00:03:54,160 --> 00:03:58,450
end execution when this happens. So when somebody wants to buy coffee,

64
00:03:58,480 --> 00:04:03,160
this is the line that they see. But when a maintenance guy comes along,

65
00:04:03,160 --> 00:04:05,140
then they should be able to enter something.

66
00:04:05,500 --> 00:04:08,290
And if this choice happens to equal the secret code,

67
00:04:08,590 --> 00:04:13,090
which is off, then in this case we should stop the while loop and exit.

68
00:04:13,510 --> 00:04:18,510
So that gives us a way of changing this true into some other form of variable,

69
00:04:18,870 --> 00:04:22,320
right? So we could create a new variable code is_on,

70
00:04:22,650 --> 00:04:27,180
start it off as true and while the machine is on,

71
00:04:27,510 --> 00:04:31,530
then it should continue to loop through and ask the user for their choice.

72
00:04:31,890 --> 00:04:35,280
But if the choice happens to be off, then we're going to turn

73
00:04:35,280 --> 00:04:39,060
that is_on into false. Now,

74
00:04:39,060 --> 00:04:40,650
if we run our code again,

75
00:04:40,650 --> 00:04:44,790
so now that you've run it once you can either stop it or you can rerun it,

76
00:04:45,390 --> 00:04:49,770
and now it's going to stop your existing code and rerun the code.

77
00:04:50,040 --> 00:04:52,140
So if you don't want to see this dialogue every time,

78
00:04:52,170 --> 00:04:55,230
then just check this box and then click stop and rerun.

79
00:04:55,950 --> 00:05:00,950
So now if we make a selection or we say something basically anything other than

80
00:05:01,380 --> 00:05:02,970
the key word, which is off,

81
00:05:03,240 --> 00:05:06,810
it's going to loop back and forth and keep prompting us.

82
00:05:07,170 --> 00:05:12,170
But if I say off, then the machine turns off and you can see that I've now exited

83
00:05:12,870 --> 00:05:16,920
the program. Now we've tackled 1 and 2.  

84
00:05:16,950 --> 00:05:21,930
Let's go on to number 3. When the user enters the keyword report to

85
00:05:21,930 --> 00:05:24,600
the prompt, another secret word, a report

86
00:05:24,630 --> 00:05:28,410
should be generated that shows the current resource values. For example,

87
00:05:28,410 --> 00:05:33,150
water, milk, coffee, and money. So how can we do that? Well, firstly,

88
00:05:33,180 --> 00:05:36,360
we don't actually have a variable that holds the amount of money.

89
00:05:36,690 --> 00:05:37,950
So let's create something,

90
00:05:37,950 --> 00:05:41,940
let's call it profit maybe and set it to equal zero to begin with.

91
00:05:42,240 --> 00:05:44,790
Our machine has an empty money box in the beginning.

92
00:05:45,390 --> 00:05:48,720
So now we have to check to see, well, elif

93
00:05:48,750 --> 00:05:52,590
the choice was equal to report. Well, in this case,

94
00:05:52,620 --> 00:05:57,620
we have to generate a report and the report is basically going to print all the

95
00:05:58,820 --> 00:06:00,500
values of these resources.

96
00:06:01,010 --> 00:06:06,010
So I'm simply going to copy the expected output and I'm going to paste it here.

97
00:06:07,550 --> 00:06:12,080
And then we can try and turn that into print statements,

98
00:06:12,170 --> 00:06:16,220
making it a dynamic instead of hard-coded. In my case,

99
00:06:16,220 --> 00:06:19,670
I want to add print in front of all of these lines.

100
00:06:19,790 --> 00:06:23,990
And previously we've been doing this just by writing it one by one,

101
00:06:23,990 --> 00:06:25,970
and then maybe we could copy and paste it.

102
00:06:26,330 --> 00:06:30,890
But let me show you a quick tip that you can do in PyCharm. If you're on Windows,

103
00:06:30,920 --> 00:06:35,510
hold down the alt and the shift key on your keyboard. If you are on a Mac,

104
00:06:35,540 --> 00:06:37,790
hold down the option and the shift key.

105
00:06:38,300 --> 00:06:42,710
Now click at the beginning and hold and drag down.

106
00:06:43,580 --> 00:06:45,470
So if that doesn't work, try out a few times,

107
00:06:45,470 --> 00:06:49,400
you'll get the hang of it eventually. But notice how I've now got four cursors

108
00:06:49,520 --> 00:06:52,580
and that means when I write print, check this out.

109
00:06:53,870 --> 00:06:54,703
Isn't that cool?

110
00:06:55,550 --> 00:06:59,780
I've managed to write on four lines at once because I need that repeat

111
00:06:59,780 --> 00:07:03,980
functionality and this is a way of doing multiline editing.

112
00:07:04,190 --> 00:07:07,910
Remember that shortcut and use it in the future if you find it useful.

113
00:07:08,480 --> 00:07:13,430
So I'm actually going to change this all into fstrings because I want to change

114
00:07:13,460 --> 00:07:16,160
these numbers instead of being hard-coded,

115
00:07:16,490 --> 00:07:19,700
I want to insert them into here using the curly braces.

116
00:07:20,210 --> 00:07:23,120
The water is stored under resources,

117
00:07:23,510 --> 00:07:26,270
and then it's in the key called water.

118
00:07:27,830 --> 00:07:31,670
And now notice how I've got a outer double quote,

119
00:07:31,910 --> 00:07:33,770
so I can't have an inner double quote.

120
00:07:33,770 --> 00:07:37,100
So I'm going to change this into single quotes instead,

121
00:07:38,960 --> 00:07:42,530
like, so. And I'm going to do the same for milk and coffee.

122
00:07:44,420 --> 00:07:48,590
So now I've added the water, milk, and coffee into my print statement.

123
00:07:48,620 --> 00:07:50,990
All I have left is the money.

124
00:07:51,230 --> 00:07:56,230
So let's delete the value and let's insert that profit into here.

125
00:07:57,020 --> 00:08:00,170
Now let's run our code again and let's check it out.

126
00:08:00,650 --> 00:08:05,650
If I type report it should now give me a report of all the current values and

127
00:08:06,140 --> 00:08:10,130
money is equal to $0 because that's what we start off with.

128
00:08:11,120 --> 00:08:14,540
We're now ready to tackle number 4. Here

129
00:08:14,570 --> 00:08:19,370
we have to check that when the user chooses a drink, we're going to check

130
00:08:19,370 --> 00:08:23,360
if there are enough resources to make that particular drink they chose.

131
00:08:23,690 --> 00:08:26,630
For example, if a latte requires 200 ml of water

132
00:08:26,930 --> 00:08:29,390
but there's only 100ml left in the machine,

133
00:08:29,750 --> 00:08:32,960
it should not make the drink because it actually can't make the drink

134
00:08:33,289 --> 00:08:37,390
and it's going to print out, 'Sorry, there's not enough water' or not enough milk,

135
00:08:37,440 --> 00:08:39,320
not enough coffee, whatever it may be.

136
00:08:39,770 --> 00:08:42,350
So let's tackle this particular checkpoint.

137
00:08:43,909 --> 00:08:48,650
Now that I've got the if choices equal off, if choice equals report.

138
00:08:48,980 --> 00:08:50,990
Now, if it's not either of those,

139
00:08:51,020 --> 00:08:54,080
then they're probably going to be entering the name of a drink.

140
00:08:54,380 --> 00:08:56,820
So let's catch that using an else statement.

141
00:08:57,480 --> 00:08:59,430
And then inside this else statement

142
00:08:59,430 --> 00:09:04,350
I'm going to get hold of the particular drink that they ordered by tapping into

143
00:09:04,350 --> 00:09:09,120
our menu dictionary and then using that choice they typed in as the key.

144
00:09:09,630 --> 00:09:14,190
Let's say that the particular drink that they chose is equal to menu

145
00:09:14,610 --> 00:09:18,480
and then the key is of course going to be the choice.

146
00:09:18,930 --> 00:09:23,930
So now if I just print this drink and I run my code..

147
00:09:24,270 --> 00:09:29,270
So the shortcut for running is actually holding down the control and R and now

148
00:09:29,730 --> 00:09:34,200
it can go down here and you can see it's asking me for what I would like,

149
00:09:34,230 --> 00:09:38,010
so I'm going to choose latte. And what's going to be printed

150
00:09:38,040 --> 00:09:43,040
is the latte entry in my recipes dictionary up here, so this particular

151
00:09:44,010 --> 00:09:44,843
value.

152
00:09:46,050 --> 00:09:50,070
Now that I've got this value stored inside a variable called drink,

153
00:09:50,340 --> 00:09:55,340
well then I can tap into its ingredients and loop through each of the ingredients

154
00:09:56,160 --> 00:10:00,600
comparing it against the resources and seeing if there's enough.

155
00:10:00,990 --> 00:10:04,680
Now this is a little bit of functionality that should probably be self-

156
00:10:04,680 --> 00:10:07,950
contained. So instead of just printing the drink,

157
00:10:07,950 --> 00:10:11,520
I'm actually going to create a new function. So up here,

158
00:10:11,520 --> 00:10:15,930
I'm going to create a new function with our def and I'm going to call it is_

159
00:10:15,960 --> 00:10:17,940
resource_sufficient.

160
00:10:20,370 --> 00:10:25,370
And this is_resource_efficient is going to take the order ingredients as a

161
00:10:27,180 --> 00:10:29,910
input and then it's going to work on that.

162
00:10:29,910 --> 00:10:34,860
So if we want to call that function and pass in the order ingredients we'll have

163
00:10:34,860 --> 00:10:36,930
to call is_resource_efficient

164
00:10:37,410 --> 00:10:42,410
and then the other ingredients will be from the drink and then getting hold of

165
00:10:43,350 --> 00:10:46,470
the values under the key ingredients.

166
00:10:48,860 --> 00:10:49,580
All right.

167
00:10:49,580 --> 00:10:54,350
So under this particular key, it will fetch this particular dictionary.

168
00:10:54,710 --> 00:10:58,880
And this is the dictionary that's going to be passed over to this function as

169
00:10:58,880 --> 00:10:59,713
the input.

170
00:11:00,140 --> 00:11:04,130
So now that we have a hold of a dictionary with all the ingredients that are

171
00:11:04,130 --> 00:11:06,950
required and the amount of each ingredient,

172
00:11:07,250 --> 00:11:09,950
we can now compare it against our resources

173
00:11:09,980 --> 00:11:14,980
which is a very similar dictionary with the resources and the amount that's left

174
00:11:15,800 --> 00:11:16,633
in the machine.

175
00:11:17,750 --> 00:11:22,750
We can loop through the order ingredients and for each of the items in the

176
00:11:23,720 --> 00:11:24,380
ingredients,

177
00:11:24,380 --> 00:11:29,380
we're going to check to see if the order ingredients at that particular key,

178
00:11:30,080 --> 00:11:35,080
so this is getting hold of the value, is greater than or equal to the resources

179
00:11:37,700 --> 00:11:41,090
using the same particular key. For example,

180
00:11:41,090 --> 00:11:43,580
if we were looking at the first example,

181
00:11:43,940 --> 00:11:46,580
the item would be equal to water.

182
00:11:47,090 --> 00:11:51,020
So if we fetch the value from order ingredients

183
00:11:51,050 --> 00:11:54,010
with the key of water, we should get of 200.

184
00:11:54,460 --> 00:11:59,460
And we would now test to see if 200 is greater than or equal to the 300 that

185
00:12:02,110 --> 00:12:05,050
we have under the resources. Well, in this case,

186
00:12:05,080 --> 00:12:09,370
then we should probably tell the user that we actually can't make it.

187
00:12:09,370 --> 00:12:14,370
So let's put an if statement there and I'm going to use this same string here to

188
00:12:15,880 --> 00:12:16,713
print it out.

189
00:12:18,340 --> 00:12:22,000
Now notice when I pasted that string in and

190
00:12:22,000 --> 00:12:27,000
it has the double quotes from the PDF file here that it's actually not being

191
00:12:27,910 --> 00:12:29,740
recognized and I'm getting an error here.

192
00:12:30,220 --> 00:12:33,820
And the important thing to know is that there's a difference between decorative

193
00:12:33,820 --> 00:12:35,260
double quotes, like these,

194
00:12:35,320 --> 00:12:38,680
which looked different for the beginning quote and the end quote.

195
00:12:39,130 --> 00:12:43,060
And then there are Programming double quotes which look like this,

196
00:12:43,060 --> 00:12:44,770
so I'm going to select this whole line

197
00:12:45,070 --> 00:12:50,070
and I'm going to add a double quote and notice how they look identical from the

198
00:12:50,260 --> 00:12:54,550
front and the back. So now it's going to print, Sorry

199
00:12:54,550 --> 00:12:56,050
there is not enough.

200
00:12:56,140 --> 00:12:59,560
And the enough of what? It's going to be

201
00:12:59,590 --> 00:13:01,990
the item that we're currently looping through.

202
00:13:02,500 --> 00:13:04,210
So let's change that to an fstring

203
00:13:04,540 --> 00:13:08,080
which makes that an active piece of code that's going to be inserted.

204
00:13:08,980 --> 00:13:09,880
And in this case,

205
00:13:09,910 --> 00:13:14,530
we're going to return false because there is not enough resources.

206
00:13:14,980 --> 00:13:16,210
But otherwise,

207
00:13:16,450 --> 00:13:21,130
if we managed to get to the end of the for loop and we still haven't returned or

208
00:13:21,130 --> 00:13:25,420
exited the function by returning false, then in this case

209
00:13:25,450 --> 00:13:26,560
we can return true.

210
00:13:26,980 --> 00:13:30,520
So if this particular logic is a little bit confusing for you,

211
00:13:30,520 --> 00:13:35,080
you could have something like, like this.

212
00:13:35,110 --> 00:13:39,730
So you have is_enough = true, and you could change is_enough

213
00:13:41,380 --> 00:13:42,640
to false.

214
00:13:42,910 --> 00:13:46,810
If any of the order ingredients are greater than the resources.

215
00:13:47,380 --> 00:13:51,250
And finally at the end, you could return is_enough.

216
00:13:51,460 --> 00:13:55,630
So basically it stays true unless one of these if statements gets activated.

217
00:13:56,800 --> 00:14:01,540
But for simplicity sake, I'm actually just going to keep it simple like this.

218
00:14:02,140 --> 00:14:04,720
And we're now ready to receive that result here

219
00:14:05,140 --> 00:14:07,270
so we can put an if statement here.

220
00:14:07,390 --> 00:14:10,630
If the resources are sufficient for the drink,

221
00:14:11,080 --> 00:14:14,800
then we can proceed to continue to the next step.

222
00:14:15,970 --> 00:14:18,580
The next step is to process coins.

223
00:14:18,730 --> 00:14:21,820
The user's going to be asked for the number of quarters

224
00:14:21,820 --> 00:14:24,070
they have, the number of dimes, nickels, and pennies,

225
00:14:24,460 --> 00:14:26,950
and you have to remember their values.

226
00:14:26,980 --> 00:14:31,000
So if you're from the US this shouldn't be a problem. But if you're like me

227
00:14:31,030 --> 00:14:33,610
somebody who's not from the US, um,

228
00:14:33,640 --> 00:14:36,940
I actually find it really confusing when I go to the States.

229
00:14:37,450 --> 00:14:41,860
I always think that the larger coin, that the nickel, should be worth more than

230
00:14:41,860 --> 00:14:44,200
the dime, but I think it was just me being silly.

231
00:14:45,070 --> 00:14:49,570
So we're going to ask the user to insert some coins, we're going to process it

232
00:14:49,630 --> 00:14:52,340
and then we're going to calculate the total value of the coins

233
00:14:52,340 --> 00:14:54,590
they inserted. That, to me,

234
00:14:54,590 --> 00:14:57,440
sounds like it should be a separate function as well.

235
00:14:58,040 --> 00:15:02,120
So let's create another function here, which I'm going to call process_coins.

236
00:15:04,130 --> 00:15:06,410
And this is not going to take any input,

237
00:15:06,470 --> 00:15:10,610
but it is going to return the total value of the coins inserted.

238
00:15:11,270 --> 00:15:13,310
Now, how do we process coins? Well,

239
00:15:13,310 --> 00:15:18,310
first we can print to ask them to please insert coins.

240
00:15:19,340 --> 00:15:23,780
And then afterwards, we're going to somehow calculate a total, right?

241
00:15:23,810 --> 00:15:25,940
This is the variable that we're going to keep track of

242
00:15:26,270 --> 00:15:29,150
and we're going to return as the output of this function.

243
00:15:29,930 --> 00:15:34,160
The total is going to be calculated based on the four types of coins.

244
00:15:34,670 --> 00:15:38,600
So the first question we're going to ask them is how many quarters?

245
00:15:40,700 --> 00:15:43,670
And this of course is going to be a whole number,

246
00:15:43,670 --> 00:15:46,910
so we're going to turn it from a string into an integer.

247
00:15:47,570 --> 00:15:51,860
And we know that each quarter is worth 0.25

248
00:15:51,860 --> 00:15:53,090
of a dollar,

249
00:15:53,390 --> 00:15:57,470
so we can multiply the number of quarters by 0.25

250
00:15:57,770 --> 00:15:59,720
and then we'll get the monetary value.

251
00:16:01,190 --> 00:16:06,190
Now we'll need to do the same thing for a bunch of other coins.

252
00:16:06,980 --> 00:16:09,860
So instead of quarters, this is going to be dimes,

253
00:16:10,130 --> 00:16:14,690
and then it's going to be nickels and finally,

254
00:16:14,690 --> 00:16:18,920
it's going to be pennies. Dimes are worth 10 cents,

255
00:16:19,310 --> 00:16:21,380
nickels are worth 5 cents,

256
00:16:22,010 --> 00:16:26,030
and pennies are worth 1 cent. Now,

257
00:16:26,060 --> 00:16:30,950
instead of just setting the totals of each of these values, every subsequent one

258
00:16:30,980 --> 00:16:32,240
other than the first one

259
00:16:32,240 --> 00:16:35,810
which remember creates this variable and sets its value,

260
00:16:36,230 --> 00:16:41,230
every other one is just going to be added to the current value like this.

261
00:16:42,620 --> 00:16:44,840
So now at the very end of all of this,

262
00:16:44,870 --> 00:16:48,260
we're going to return the total as the output.

263
00:16:48,740 --> 00:16:52,850
And whenever you have something that returns like both of these functions,

264
00:16:53,210 --> 00:16:56,960
you should probably be adding a docstring. So in this case,

265
00:16:56,960 --> 00:16:58,280
this returns

266
00:16:58,280 --> 00:17:02,870
the total calculated from coins

267
00:17:02,870 --> 00:17:06,349
inserted. And in this case,

268
00:17:06,380 --> 00:17:11,380
what happens is it returns true when order can be made and false

269
00:17:15,500 --> 00:17:19,130
if ingredients are insufficient.

270
00:17:20,990 --> 00:17:25,160
Now let's call this function that we created, process_coins.

271
00:17:25,849 --> 00:17:28,310
If there's enough resources to make the drink,

272
00:17:28,339 --> 00:17:31,520
then the next step is to actually ask them for the money.

273
00:17:31,820 --> 00:17:34,820
So here is where we're going to call process coins.

274
00:17:35,450 --> 00:17:40,400
And notice when I write this and I hover over it, you can see that docstring

275
00:17:40,400 --> 00:17:43,700
we just wrote, returns the total from coins inserted.

276
00:17:44,990 --> 00:17:47,180
That means this is going to return

277
00:17:47,330 --> 00:17:52,110
and we need to capture the user's payment in this variable.

278
00:17:52,110 --> 00:17:56,760
So this returns the output replaces this function call,

279
00:17:57,060 --> 00:18:01,230
and then it gets saved inside this variable called payment. Now,

280
00:18:01,230 --> 00:18:05,340
what are we going to do with this payment? Well, that goes onto the next step,

281
00:18:05,790 --> 00:18:08,970
which is to check that the transaction was successful.

282
00:18:09,270 --> 00:18:13,380
So we have to make sure that the user has inserted enough money to actually

283
00:18:13,380 --> 00:18:18,060
purchase the drink they wanted. But each drink of course has a different price.

284
00:18:18,330 --> 00:18:22,920
So if the user inserts enough money, then we're going to give them some change.

285
00:18:23,250 --> 00:18:26,910
But if they haven't inserted enough money, then we're going to say, sorry,

286
00:18:26,910 --> 00:18:29,460
that's not enough money. And the money is refunded.

287
00:18:30,240 --> 00:18:33,990
But if they have inserted enough money then the cost of the drink is going to be

288
00:18:33,990 --> 00:18:38,700
added to the machine as the profit. So the next time when we trigger the report,

289
00:18:38,730 --> 00:18:42,570
then we're going to get to see the increase in the monetary value.

290
00:18:44,010 --> 00:18:44,490
Again,

291
00:18:44,490 --> 00:18:48,900
let's create a new function and let's get rid of some of these squiggly lines by

292
00:18:48,900 --> 00:18:51,630
adding enough spaces in between the functions.

293
00:18:52,530 --> 00:18:56,370
This one I'm going to call is_transaction_successful,

294
00:18:58,290 --> 00:19:00,810
because that's basically what we're going to be checking.

295
00:19:01,380 --> 00:19:03,990
And it's going to take two inputs.

296
00:19:04,110 --> 00:19:08,520
It's going to take a input in terms of the amount of money that was received,

297
00:19:09,180 --> 00:19:14,130
and it's also going to have another input, which is cost of the drink.

298
00:19:15,060 --> 00:19:20,060
This function's goal is to return true when the payment is accepted or it's

299
00:19:24,570 --> 00:19:25,980
going to return false

300
00:19:26,370 --> 00:19:29,610
if the money is insufficient.

301
00:19:29,630 --> 00:19:30,463
Uhm

302
00:19:32,390 --> 00:19:36,410
Notice how there's this line to the right here of your editor.

303
00:19:36,890 --> 00:19:41,890
Basically what happens is if you have a line of code that's a little bit too

304
00:19:41,930 --> 00:19:45,320
long past the recommendation from PEP 8,

305
00:19:45,650 --> 00:19:50,150
you can see that PEP 8 recommends that a line should not be longer than 120

306
00:19:50,150 --> 00:19:50,983
characters

307
00:19:51,140 --> 00:19:54,650
because it's very hard to read for somebody scrolling around like this.

308
00:19:54,980 --> 00:19:55,880
So in this case,

309
00:19:55,880 --> 00:20:00,020
they would want you to put it onto a new line so that you don't have to scroll

310
00:20:00,020 --> 00:20:03,500
and you can see it all on the same screen. But in our case,

311
00:20:03,500 --> 00:20:07,520
this is not a problem because we have not exceeded the line length 

312
00:20:07,520 --> 00:20:08,353
recommendation.

313
00:20:09,590 --> 00:20:13,790
So how are you going to check if the transaction is successful?

314
00:20:14,420 --> 00:20:14,690
Well,

315
00:20:14,690 --> 00:20:19,690
if the money received is greater or equal to the cost of the drink, well in this case

316
00:20:21,770 --> 00:20:26,300
that means we should return true, right? The transaction is successful.

317
00:20:26,990 --> 00:20:30,530
And if it's not the case, if it's the opposite case,

318
00:20:30,860 --> 00:20:34,160
then we're going to print, Sorry that's not enough money.

319
00:20:34,220 --> 00:20:36,380
And the money is refunded to them.

320
00:20:36,620 --> 00:20:37,453
Right.

321
00:20:39,590 --> 00:20:44,420
So let's print that here. And we're also going to return false.

322
00:20:44,960 --> 00:20:48,340
Remember that the return has to be the last thing in your function.

323
00:20:48,400 --> 00:20:52,420
If you put this above the print statement then the print statement will never

324
00:20:52,420 --> 00:20:55,840
get called, and that's why you have this highlight. And if you click on it,

325
00:20:55,840 --> 00:20:58,810
you can see that it tells you this code is unreachable.

326
00:21:00,520 --> 00:21:04,780
So there's a lot of these little hints and tips that really help you when you're

327
00:21:04,780 --> 00:21:05,613
developing.

328
00:21:06,340 --> 00:21:10,990
But if the user has inserted enough money then the cost of the drink should be

329
00:21:10,990 --> 00:21:15,310
added to the machine as the profit so that we can see it in the next time report

330
00:21:15,310 --> 00:21:16,143
is triggered.

331
00:21:16,420 --> 00:21:21,420
So this means that if this money_received is greater or equal to the drink cost,

332
00:21:22,420 --> 00:21:27,420
then we're going to add to this variable called profit that we have up here,

333
00:21:28,870 --> 00:21:30,340
which starts out at zero,

334
00:21:30,580 --> 00:21:34,420
but we're going to add the drinks cost to profit.

335
00:21:34,720 --> 00:21:37,600
So we're going to say profit += drink_cost.

336
00:21:38,110 --> 00:21:41,740
And now you'll see an error under the profit

337
00:21:42,070 --> 00:21:45,100
because this is acting inside

338
00:21:45,130 --> 00:21:50,130
a local scope and profit is outside in the global scope.

339
00:21:50,830 --> 00:21:54,550
So in order to reach it, we have to say global profit.

340
00:21:56,260 --> 00:22:01,260
And the final part of checking the transaction is seeing if the user has

341
00:22:01,420 --> 00:22:06,070
inserted too much money then the machine is going to offer change. For example,

342
00:22:06,340 --> 00:22:11,080
here is however many dollars in change and the change should be rounded to two

343
00:22:11,080 --> 00:22:15,760
decimal places. Again, it's going to be inside this if statement.

344
00:22:16,420 --> 00:22:21,130
So the change is going to be equal to the amount of money received,

345
00:22:21,430 --> 00:22:23,740
subtracting the drink cost.

346
00:22:24,280 --> 00:22:27,430
And this of course could be any number of decimal places.

347
00:22:28,060 --> 00:22:30,040
So we can use the round function

348
00:22:30,040 --> 00:22:34,150
which you've seen a long time ago to round this number

349
00:22:34,510 --> 00:22:38,230
and the second