1 00:00:05,320 --> 00:00:08,980 So I continue on with that discussion of dictionaries in Python, 2 00:00:08,980 --> 00:00:11,260 that we've worked on in the last two videos. 3 00:00:11,260 --> 00:00:14,510 Again, just recapping what we did in these last few lines. 4 00:00:14,510 --> 00:00:16,640 We had fruit and it's called keys. 5 00:00:16,640 --> 00:00:18,730 So we got a view object. 6 00:00:18,730 --> 00:00:20,780 When we use the dot keys, that's what we get. 7 00:00:20,780 --> 00:00:24,030 We get a special type, sort of like a list, but it's a view object. 8 00:00:24,030 --> 00:00:26,960 We then printed that out so you can see it on the screen Then we add it 9 00:00:26,960 --> 00:00:30,150 a new item to the dictionary and when we print it out that fruit case again, 10 00:00:30,150 --> 00:00:34,980 even though we haven't directly updated that variable, it was updated by Python. 11 00:00:34,980 --> 00:00:36,400 So it happened behind the scenes. 12 00:00:36,400 --> 00:00:39,040 You can see the tomato was added in the second example. 13 00:00:39,040 --> 00:00:42,270 That again is the only way that view objects can be updated. 14 00:00:42,270 --> 00:00:46,090 Sort of indirectly with the dictionary that's happening behind the scenes. 15 00:00:46,090 --> 00:00:49,440 So we can't add items, and using delete we get an error here. 16 00:00:49,440 --> 00:00:52,600 What we can do is we can convert them to lists. 17 00:00:52,600 --> 00:00:56,680 So we can convert them to lists, and you saw us using the list method. 18 00:00:56,680 --> 00:00:58,220 The list function I should say there list. 19 00:00:58,220 --> 00:01:01,210 And we were quite able to actually convert that to list and 20 00:01:01,210 --> 00:01:03,130 then use the sort function to sort them. 21 00:01:03,130 --> 00:01:07,210 But before we leave our fruit and move on there's one more view we should look at 22 00:01:07,210 --> 00:01:11,550 and that's the items method which returns a dict_items object, which 23 00:01:11,550 --> 00:01:15,690 is another dynamic view object that consists of key and value tuples as well. 24 00:01:15,690 --> 00:01:18,030 So to do that We'll get rid of this code. 25 00:01:19,360 --> 00:01:23,150 Cut that out. Let's close out the run window for now. 26 00:01:24,280 --> 00:01:27,040 And we'll put the print in. 27 00:01:27,040 --> 00:01:27,640 Print fruit. 28 00:01:28,910 --> 00:01:32,190 We can do printfruit.items. 29 00:01:33,990 --> 00:01:35,590 Oops, semicolon there, wrong language. 30 00:01:35,590 --> 00:01:39,350 [LAUGH] Run that, and you can see we've got a different output. 31 00:01:39,350 --> 00:01:45,230 It looks very similar if you recall our videos on tuples. 32 00:01:45,230 --> 00:01:49,190 And as it turns out, we can produce a tuple from it using our tuple function. 33 00:01:49,190 --> 00:01:54,580 So we could do f_tuple equals tuple, they 34 00:01:55,790 --> 00:02:00,580 give us a built in function, fruit.items, 35 00:02:00,580 --> 00:02:06,070 and print f_tuple, like so. 36 00:02:06,070 --> 00:02:11,890 We can run that, and I forgot to put some brackets in there, cuz it's a method call. 37 00:02:11,890 --> 00:02:15,310 Run that And on the last line now you can see we have a regular tuple. 38 00:02:15,310 --> 00:02:19,760 And of course, from that point on we can then use tuple, or 39 00:02:19,760 --> 00:02:25,060 in the case the variable tuple just like we used tuples in any early videos. 40 00:02:25,060 --> 00:02:29,120 For example, we could do something like for snack N 41 00:02:31,350 --> 00:02:37,430 quatupple item common description, 42 00:02:37,430 --> 00:02:46,290 equals snack print item plus is past description. 43 00:02:46,290 --> 00:02:50,440 And we can run that, and you can see we've got our items there. 44 00:02:50,440 --> 00:02:51,940 What was the key from the dictionary, and 45 00:02:51,940 --> 00:02:55,620 also the value from the dictionary because we've created a topple. 46 00:02:55,620 --> 00:02:58,340 We've then got them in our description variables. 47 00:02:58,340 --> 00:03:00,890 Now this wouldn't be Python if it wasn't possible to go the other way. 48 00:03:00,890 --> 00:03:05,970 In other words to create a dictionary from topples of key values pairs, and 49 00:03:05,970 --> 00:03:08,530 the dict constructor allows us to do just that. 50 00:03:08,530 --> 00:03:13,550 So I walk down here On this line we could type print. 51 00:03:13,550 --> 00:03:17,090 Then use the built-in dict function and 52 00:03:17,090 --> 00:03:19,360 pass a tuple to it, the tuple that we've created. 53 00:03:20,520 --> 00:03:27,540 If you run that As you can see that there, that's now just our regular dictionary, 54 00:03:27,540 --> 00:03:30,790 probably not terribly exciting to you because all we've really done is got 55 00:03:30,790 --> 00:03:35,880 the original directory back that we had that we created. 56 00:03:35,880 --> 00:03:36,740 On line one. 57 00:03:36,740 --> 00:03:40,610 But what it does do is demonstrate how a dictionary can be created from a tuple 58 00:03:40,610 --> 00:03:42,260 which is extremely useful. 59 00:03:42,260 --> 00:03:46,360 There is a lot of interaction between dictionaries, tuples and lists. 60 00:03:46,360 --> 00:03:48,210 And later in the course we'll summarize everything we've 61 00:03:48,210 --> 00:03:49,400 done with these data structures. 62 00:03:49,400 --> 00:03:53,290 And what we'll also do is include a list of all the methods that apply to each one. 63 00:03:53,290 --> 00:03:55,360 And now moving onto something that's completely different, 64 00:03:55,360 --> 00:03:56,990 I'll just close down that one window. 65 00:03:56,990 --> 00:03:59,180 Now rather than try to cover everything at once, and 66 00:03:59,180 --> 00:04:02,460 have it all become terribly overwhelming, what we've been doing is we've been 67 00:04:02,460 --> 00:04:06,680 introducing methods and functions as it becomes appropriate to use them. 68 00:04:06,680 --> 00:04:10,910 So now's a good time to introduce another of the string methods Which is joined. 69 00:04:10,910 --> 00:04:14,610 By now you should be used to the idea of mutable and immutable objects. 70 00:04:14,610 --> 00:04:16,519 If you remember strings are immutable. 71 00:04:16,519 --> 00:04:19,690 As a result this means that it's not at all efficient to concatenate 72 00:04:19,690 --> 00:04:21,399 strings in a loop. 73 00:04:21,399 --> 00:04:26,260 Anytime you concatenate a string to an existing string, the new string has to be 74 00:04:26,260 --> 00:04:30,780 created and if that's done in a loop it becomes expensive and slow. 75 00:04:30,780 --> 00:04:32,910 So you really do want to avoid that. 76 00:04:32,910 --> 00:04:35,740 The string join method is there to actually help you. 77 00:04:35,740 --> 00:04:39,620 It actually takes a sequence and produces a string from it. 78 00:04:39,620 --> 00:04:42,500 So the items in the new string are separated by 79 00:04:42,500 --> 00:04:44,350 the stream that join was called upon. 80 00:04:44,350 --> 00:04:46,990 So as said a lot of these things are probably easier to demonstrate rather then 81 00:04:46,990 --> 00:04:48,200 for me to explain it any further. 82 00:04:48,200 --> 00:04:53,190 So I'm gonna create a new file now to leave the [INAUDIBLE] as it was. 83 00:04:53,190 --> 00:04:53,860 New Python file. 84 00:04:53,860 --> 00:04:58,250 And we'll just call this one join for want of a better word. 85 00:04:58,250 --> 00:05:00,480 So let's create a list first. 86 00:05:00,480 --> 00:05:07,340 And myList = ["a","b","c","d"]. 87 00:05:07,340 --> 00:05:10,870 newString = "", just an empty string for now. 88 00:05:11,910 --> 00:05:16,470 And we're going to go through, iterate through my list. 89 00:05:16,470 --> 00:05:21,580 We'll see in my list newString += c + ", " like so, and 90 00:05:21,580 --> 00:05:27,140 then we'll print(newString). 91 00:05:27,140 --> 00:05:29,170 So I consider this first example, and 92 00:05:29,170 --> 00:05:33,320 I will just make sure I'm running this right one, running join. 93 00:05:33,320 --> 00:05:35,730 ABCD so you can see has appeared on the screen. 94 00:05:35,730 --> 00:05:38,840 So as I mentioned this is not a good way of producing code. 95 00:05:38,840 --> 00:05:40,260 So, a couple of problems here, 96 00:05:40,260 --> 00:05:43,360 leaving aside the fact firstly there's a comma on the end of our output. 97 00:05:43,360 --> 00:05:47,530 It's also inefficient because every time through the loop it's creating 98 00:05:47,530 --> 00:05:52,520 a new copy of new string because again the strings that we're using are immutable. 99 00:05:52,520 --> 00:05:56,410 Now augmented assignment will help We did say that talked about that earlier in this 100 00:05:56,410 --> 00:06:00,090 course it does try to update the variable in place where possible but 101 00:06:00,090 --> 00:06:03,170 this is not one of those times where its possible so in other words because strings 102 00:06:03,170 --> 00:06:06,990 are unbeatable augmented a summit isn't gonna help you so what you'd want 103 00:06:06,990 --> 00:06:11,850 to do in this scenario is you want to use join to fix this problem and the way we 104 00:06:11,850 --> 00:06:16,440 would use that Instead of putting plus equals we will delete that out. 105 00:06:16,440 --> 00:06:20,720 We put newString = ", ".join(myList). 106 00:06:20,720 --> 00:06:21,470 And we run that. 107 00:06:23,020 --> 00:06:29,100 Notice we haven't got the trailing comma now. 108 00:06:29,100 --> 00:06:30,760 So is much more efficient. 109 00:06:30,760 --> 00:06:33,500 It also solves the problem of the trailing comme, as you can see there. 110 00:06:33,500 --> 00:06:36,780 And it's really much more Pythonic in that 111 00:06:36,780 --> 00:06:40,970 it's working in a way that Python would intend to work for something like this. 112 00:06:40,970 --> 00:06:44,890 So the way this particular method works is it creates a new string by taking each 113 00:06:44,890 --> 00:06:48,360 item in a sequence which is a list as you can see that are created on line 1. 114 00:06:48,360 --> 00:06:53,480 And separates the item with a string comma that join is actually invoked on. 115 00:06:53,480 --> 00:06:56,430 So we can use any sequence tied by some parameter to join. 116 00:06:56,430 --> 00:06:59,560 So for example instead of a list we can pass another string. 117 00:06:59,560 --> 00:07:01,350 So I'm just gonna place some code in here. 118 00:07:01,350 --> 00:07:03,000 You see what I mean. 119 00:07:03,000 --> 00:07:08,210 So let's change that to letters. 120 00:07:08,210 --> 00:07:10,130 And instead of my list, make that letters. 121 00:07:10,130 --> 00:07:13,630 Of course, you can see See the letters there is now a string instead of a list. 122 00:07:13,630 --> 00:07:17,480 If we run that then we get the same output as you can see. 123 00:07:17,480 --> 00:07:21,450 The same processing, I've since gone from a to Zed because the input was 124 00:07:21,450 --> 00:07:25,400 a string in this case containing the letters a to z. 125 00:07:25,400 --> 00:07:28,010 The other thing to remember is that the string we called joined method on can be 126 00:07:28,010 --> 00:07:29,800 quite complex as well. 127 00:07:29,800 --> 00:07:33,670 If I for example, come back here or close the again. 128 00:07:35,350 --> 00:07:37,880 Numbers, let's try instead of just putting a comma, we'll put 129 00:07:42,070 --> 00:07:46,280 And then .join numbers. 130 00:07:46,280 --> 00:07:50,910 Run that, you see one Mississippi, two Mississippi, three Mississippi. 131 00:07:50,910 --> 00:07:55,810 And so I probably to fix the Spacing, then again you can say 1 Mississippi, 132 00:07:55,810 --> 00:07:58,700 2 Mississippi, 3 Mississippi, and so on. 133 00:07:58,700 --> 00:08:00,150 Again in case you're wondering why, 134 00:08:00,150 --> 00:08:02,760 separating numbers with the word Mississippi is a very rough way to count 135 00:08:02,760 --> 00:08:05,420 seconds, if you don't have a stopwatch handy. 136 00:08:05,420 --> 00:08:07,560 And you could also use 2000 in place of Mississippi. 137 00:08:07,560 --> 00:08:09,110 But anyway I'm getting off track there. 138 00:08:09,110 --> 00:08:11,900 You might have guessed that we're about to concatenate the keys of a dictionary to 139 00:08:11,900 --> 00:08:13,600 give us a stream and you'd be right. 140 00:08:13,600 --> 00:08:17,010 So let's get to doing that because of course this is all about dictionaries. 141 00:08:17,010 --> 00:08:20,340 What we're gonna do is we're going to use dictionaries to store locations in a very 142 00:08:20,340 --> 00:08:21,850 basic adventure game. 143 00:08:21,850 --> 00:08:24,920 We'll also store the available exits in another dictionary and we're gonna link 144 00:08:24,920 --> 00:08:28,790 the two together so that players can move from one location to another. 145 00:08:28,790 --> 00:08:30,870 So I'm just gonna bring a little image up on the screen now so 146 00:08:30,870 --> 00:08:32,630 you can see what I'm talking about. 147 00:08:33,750 --> 00:08:35,929 You can see there that there is five locations a road, 148 00:08:35,929 --> 00:08:38,950 a hill, a building, a valley, and a forest. 149 00:08:38,950 --> 00:08:40,750 The roads are not all straight and you can see this. 150 00:08:40,750 --> 00:08:44,590 That going north from the hill takes you to the forest entering from the west. 151 00:08:44,590 --> 00:08:46,630 So you can go west from the forest to get back to the hill. 152 00:08:46,630 --> 00:08:51,100 What we are going to do What we can do is we can represent the map as a dictionary. 153 00:08:51,100 --> 00:08:54,530 And although we could use the short names of the location as the key, 154 00:08:54,530 --> 00:08:57,810 what we're gonna do is use numbers instead cuz that's easy to read initially. 155 00:08:57,810 --> 00:09:00,370 And if you want to replace one with rho etc., a simple search and 156 00:09:00,370 --> 00:09:02,540 replace will do that once everything's working. 157 00:09:02,540 --> 00:09:06,590 So what I'm going to do now is just copy and paste that code for that dictionary. 158 00:09:07,960 --> 00:09:09,580 I'm just going to replace the code we worked on here. 159 00:09:09,580 --> 00:09:13,790 So I'm gonna paste it in there like so, and you can see we've got the 5 locations 160 00:09:13,790 --> 00:09:17,940 and the keys you can see for each value in the dictionary is the number, 161 00:09:17,940 --> 00:09:20,690 and then it's obviously the description, which is the, and 162 00:09:20,690 --> 00:09:23,790 the other one, the other part is the value as well for the dictionary. 163 00:09:23,790 --> 00:09:25,130 So you've got the key and the value for 164 00:09:25,130 --> 00:09:27,650 each and the 5 locations on the screen as you can see there. 165 00:09:27,650 --> 00:09:30,390 Incidentally, I think that's a lot easier to do when you're adding dictionary 166 00:09:30,390 --> 00:09:33,130 entries like this, creating a dictionary, it is better to separate them. 167 00:09:33,130 --> 00:09:35,670 So I put a comma and separate them on a separate them on a separate line. 168 00:09:35,670 --> 00:09:39,210 It's just easier to read and sort of avoids your dictionaries becoming a little 169 00:09:39,210 --> 00:09:42,450 bit too messy as can happen if you've got them all sort of linked up on a line. 170 00:09:43,530 --> 00:09:45,950 You can see I did it in there as well with the fruit. 171 00:09:45,950 --> 00:09:48,380 So what we now need to do, we've got our basic locations, 172 00:09:48,380 --> 00:09:51,560 we need to represent the available exits from each location. 173 00:09:51,560 --> 00:09:55,480 Comparing to mine again is four plus one exits, north, south, east, and west, 174 00:09:55,480 --> 00:09:57,360 plus quit to exit the game. 175 00:09:57,360 --> 00:09:59,200 So quit's going to available everywhere, 176 00:09:59,200 --> 00:10:01,070 otherwise the available exits will match the map. 177 00:10:01,070 --> 00:10:05,560 So again, looking at the map again What we;re trying to do now is 178 00:10:05,560 --> 00:10:09,890 basically duplicating this set of options which direction is valid. 179 00:10:09,890 --> 00:10:10,580 A set, but 180 00:10:10,580 --> 00:10:15,100 also enabling a quit to actually enable you to quit the game at any point. 181 00:10:15,100 --> 00:10:17,850 From the road for example, we can go in all four directions, but 182 00:10:17,850 --> 00:10:19,730 if we go east to the building. 183 00:10:19,730 --> 00:10:22,550 The only exit from there is gonna be ways back to road. 184 00:10:22,550 --> 00:10:25,100 So one way we can represent this would be a dictionary with 185 00:10:25,100 --> 00:10:27,030 the directions being the key and 186 00:10:27,030 --> 00:10:31,450 the values being the location that we end up at if we go in that direction. 187 00:10:31,450 --> 00:10:34,370 So from one, remember in our key one is the road, 188 00:10:34,370 --> 00:10:38,490 if you go west from there, we'll end up at two, which is the hill. 189 00:10:38,490 --> 00:10:41,870 And if you go east We get to three, the building. 190 00:10:41,870 --> 00:10:45,100 So when we get to a new location, we should print out the description. 191 00:10:45,100 --> 00:10:47,840 And that's gonna be easy to do because each direction 192 00:10:47,840 --> 00:10:52,040 gives us the key of the destination in the locations directory, if that makes sense. 193 00:10:52,040 --> 00:10:53,780 So what I'm gonna do is paste this in now. 194 00:10:53,780 --> 00:10:59,200 Our next dictionary is going to be exits, like so. 195 00:10:59,200 --> 00:11:02,430 And you can see now that we're using a key for the direction And 196 00:11:02,430 --> 00:11:05,960 the value is of a key from the locations. 197 00:11:05,960 --> 00:11:09,480 And again, the reason we're doing that is so that we can ultimately print out 198 00:11:09,480 --> 00:11:12,850 the location when we move, where we've moved to in other words. 199 00:11:12,850 --> 00:11:14,840 So again, bringing the image back up on the screen again. 200 00:11:14,840 --> 00:11:18,780 So if we start off on the road, we get the available exits by looking at index 1. 201 00:11:18,780 --> 00:11:21,270 So I'm just going to just put that over there. 202 00:11:21,270 --> 00:11:25,090 Again the exits is represented as a list of dictionary objects. 203 00:11:25,090 --> 00:11:27,360 This contains one dictionary for each location. 204 00:11:27,360 --> 00:11:30,310 Notice this is a list of dictionary objects. 205 00:11:30,310 --> 00:11:33,920 Important distinction to locations which is just a dictionary. 206 00:11:33,920 --> 00:11:37,490 And we're doing it this way ultimately because we can index the list. 207 00:11:37,490 --> 00:11:39,260 We know that element zero is always going to be the same. 208 00:11:39,260 --> 00:11:39,830 We know that element. 209 00:11:39,830 --> 00:11:43,040 One's always going to be the same and so on and so fourth unlike a dictionary. 210 00:11:43,040 --> 00:11:46,960 And the method we come up here isn't necessarily the best way to represent 211 00:11:46,960 --> 00:11:47,880 the exists. 212 00:11:47,880 --> 00:11:51,850 For example, we could use a dictionary with the key being the location number and 213 00:11:51,850 --> 00:11:55,070 the exists perhaps the List of tuples or another dictionary. 214 00:11:55,070 --> 00:11:59,330 But it's probably easy to start this way, and sort of progress to that ladder. 215 00:11:59,330 --> 00:12:02,020 So again, if we start off on the right, we can get the available width just by 216 00:12:02,020 --> 00:12:05,070 looking at index one in the list to get the dictionary. 217 00:12:05,070 --> 00:12:06,540 So again, we start here. 218 00:12:06,540 --> 00:12:09,380 One, come over here to element one on the list. 219 00:12:09,380 --> 00:12:12,660 And, that's the valid entries, or the valid directions and 220 00:12:12,660 --> 00:12:15,630 also the quick to exit for that particular location. 221 00:12:15,630 --> 00:12:19,880 So, standing on the road, going west would go to two, location two which is the hill. 222 00:12:19,880 --> 00:12:21,240 East would go to three. 223 00:12:21,240 --> 00:12:22,550 Which is a Building. 224 00:12:22,550 --> 00:12:24,330 North will go to five which is the Forest and 225 00:12:24,330 --> 00:12:26,520 south would go t four which is a Valley. 226 00:12:26,520 --> 00:12:29,600 And again, we have the Q coming out to quit out which is going to 227 00:12:29,600 --> 00:12:31,890 basically quit the game. 228 00:12:31,890 --> 00:12:37,080 Similarly from the Hill, we get the dictionary in position two on the list. 229 00:12:37,080 --> 00:12:39,850 You can see position two has been defined there on line 10. 230 00:12:39,850 --> 00:12:42,520 The only way we can go from the hill, we can go north to go to 5, 231 00:12:42,520 --> 00:12:44,010 which of course is the forest. 232 00:12:44,010 --> 00:12:47,400 There's no other exit, other than quit, so we can't get back to the road from 233 00:12:47,400 --> 00:12:48,750 the hill, that's the way we've designed the game. 234 00:12:48,750 --> 00:12:52,020 You can see that by the arrows telling you whether it's multi-directional or 235 00:12:52,020 --> 00:12:53,260 single directional. 236 00:12:53,260 --> 00:12:56,310 So now that we've done that, a simple loop should allow us 237 00:12:56,310 --> 00:12:59,770 to allow the player to keep entering directions until it's [INAUDIBLE]. 238 00:12:59,770 --> 00:13:02,510 And each time around the loop, we'll display descriptions of the local in 239 00:13:02,510 --> 00:13:05,420 the available exits, just to make it look good. 240 00:13:05,420 --> 00:13:06,330 So let's try that. 241 00:13:08,210 --> 00:13:12,640 So I'm gonna type [INAUDIBLE] equals one, 242 00:13:12,640 --> 00:13:19,030 while true, and continue until, basically till Our quitters are selected 243 00:13:19,030 --> 00:13:23,880 available exits equals nothing for now. 244 00:13:23,880 --> 00:13:31,900 For direction in exits location we're starting off at location one. 245 00:13:31,900 --> 00:13:35,170 Again we're starting off starting on the road, number one, 246 00:13:35,170 --> 00:13:36,500 that's why I like lock equals one. 247 00:13:38,450 --> 00:13:43,650 So retrieving the dictionary from our list as you can see there for 248 00:13:43,650 --> 00:13:46,590 that particular direction, we're getting the directions and 249 00:13:46,590 --> 00:13:49,620 available booting up our list then, available exits. 250 00:13:49,620 --> 00:13:53,270 Plus equals direction. 251 00:13:55,700 --> 00:14:02,300 Like so. And then we're going to print locations 252 00:14:02,300 --> 00:14:11,300 and loc is equal to zero. 253 00:14:11,300 --> 00:14:11,800 Oops. 254 00:14:17,130 --> 00:14:21,890 Don't need a bracket there. 255 00:14:21,890 --> 00:14:28,870 Then I'm going to type direction equals input available. 256 00:14:28,870 --> 00:14:34,970 [INAUDIBLE] plus available exits Or upper. 257 00:14:34,970 --> 00:14:38,820 [NOISE] Just going to do an empty print. 258 00:14:38,820 --> 00:14:45,590 [NOISE] If direction in exits. 259 00:14:45,590 --> 00:14:49,690 [NOISE] Fixes in such a way, 260 00:14:52,580 --> 00:14:57,950 and lock equals exists so in other words if it's a valid location and 261 00:15:00,000 --> 00:15:03,970 we're gonna sign that direction. 262 00:15:05,140 --> 00:15:13,360 Else, print, You cannot go in that direction. 263 00:15:16,780 --> 00:15:20,340 The program's gonna keep looping until the player goes to location zero. 264 00:15:20,340 --> 00:15:23,340 At that point the programs gonna break out as you can see there 265 00:15:23,340 --> 00:15:24,990 on line 24 when the game ends. 266 00:15:24,990 --> 00:15:29,310 So when a direction is chosen we check that the k exists in the appropriate 267 00:15:29,310 --> 00:15:31,030 dictionary from our list of exits. 268 00:15:31,030 --> 00:15:32,680 And you can see we were doing that. 269 00:15:32,680 --> 00:15:37,350 If direction in exits location or lock, I should say the lock variable. 270 00:15:37,350 --> 00:15:41,270 And then we use the key to retrieve the next location if it does actually exist. 271 00:15:41,270 --> 00:15:44,850 The exits lock and direction. 272 00:15:44,850 --> 00:15:47,880 Again we are using that as an index into the exits list 273 00:15:47,880 --> 00:15:51,990 to retrieve the dictionary containing the available exits of that location. 274 00:15:51,990 --> 00:15:55,300 So when we get to equals one location, one gives the description, 275 00:15:55,300 --> 00:15:59,280 you are standing at the end of the rope, you cross groups, small brick building and 276 00:15:59,280 --> 00:16:00,090 we can actually run that. 277 00:16:01,630 --> 00:16:04,710 So I can see [INAUDIBLE] standing at the end of a rope before a small 278 00:16:04,710 --> 00:16:05,710 brick building. 279 00:16:05,710 --> 00:16:10,610 It shows us we can go east, south, north, quit or west. 280 00:16:10,610 --> 00:16:11,280 I can just type quit. 281 00:16:11,280 --> 00:16:14,450 You're sitting at a computer, learning [INAUDIBLE] I should say, 282 00:16:14,450 --> 00:16:16,060 then it's exited the game as you can see. 283 00:16:16,060 --> 00:16:21,050 If we run that again This time off we go south we're gonna valley 284 00:16:22,330 --> 00:16:26,670 just to confirm that it's south toward valley, so 285 00:16:26,670 --> 00:16:34,560 we shouldn't have to go back towards north so we shouldn't have to go west. 286 00:16:37,120 --> 00:16:41,320 At the top of a hill we go back to west was the hill again and 287 00:16:41,320 --> 00:16:44,320 we shouldn't now be able to go back to the valley because the way the program's been 288 00:16:44,320 --> 00:16:47,410 designed, we should only be able to go to the forest now which would be north. 289 00:16:49,320 --> 00:16:53,220 North and quit, north, you're at a forest. 290 00:16:55,270 --> 00:16:58,250 But the forest and from there we should be able to go back to the road or 291 00:16:58,250 --> 00:17:01,900 back to the hill so it should either be a south or west. 292 00:17:03,060 --> 00:17:06,180 South or west as you can see there and so on and so forth. 293 00:17:06,180 --> 00:17:06,890 We can quit out of that. 294 00:17:07,990 --> 00:17:10,720 So I'm gonna close that run window, and again, 295 00:17:10,720 --> 00:17:15,300 booting up the list in booting up a list of compatible exits, 296 00:17:15,300 --> 00:17:18,450 we're iterating through the keys of the dictionary to do that. 297 00:17:18,450 --> 00:17:21,510 But wait a minute, didn't we just say earlier in this video 298 00:17:21,510 --> 00:17:24,480 That can cannonading strings in a loop wasn't a good idea. 299 00:17:24,480 --> 00:17:27,329 Without the moment it's probably not a problem because let's face it 300 00:17:27,329 --> 00:17:29,590 there's a maximum five keys in the dictionary. 301 00:17:29,590 --> 00:17:32,620 When this game becomes the most popular multiplayer game on the internet and 302 00:17:32,620 --> 00:17:35,490 we've got thousands of people playing it in real time, that 303 00:17:35,490 --> 00:17:39,180 performance hit will become significant and things will slow probably to a call. 304 00:17:39,180 --> 00:17:44,070 So we can actually replace line 17 through 19 literally with one line. 305 00:17:44,070 --> 00:17:49,550 Let's go and do that, we'll put available x is equals dot join, 306 00:17:49,550 --> 00:17:54,600 exits lock dot 307 00:17:54,600 --> 00:17:59,590 keys which you can see is far more efficient has less lines of code to type. 308 00:17:59,590 --> 00:18:03,670 And are not going to be slowed down by that problem we would have trying to 309 00:18:03,670 --> 00:18:04,260 strings. 310 00:18:04,260 --> 00:18:09,250 And we eventually have a huge, really fast application and popular application. 311 00:18:09,250 --> 00:18:10,760 And you can see it should still work. 312 00:18:10,760 --> 00:18:12,010 We still get the same results. 313 00:18:12,010 --> 00:18:12,830 Here we can go North. 314 00:18:14,490 --> 00:18:19,090 The forest of [INAUDIBLE] he's sitting in front of a computer so that's good. 315 00:18:19,090 --> 00:18:22,310 Of course the other thing we managed to do by doing that approach was we got 316 00:18:22,310 --> 00:18:25,670 rid of the trailing comma, which is good as well. 317 00:18:25,670 --> 00:18:30,010 You might be wondering, we use direction, why didn't we use the word exit. 318 00:18:30,010 --> 00:18:33,040 Probably make more sense to say the x at the exit variable there, 319 00:18:33,040 --> 00:18:33,920 because that's really what it is. 320 00:18:33,920 --> 00:18:36,580 We're trying to find the exit to the current location. 321 00:18:36,580 --> 00:18:39,570 The reason is x is the key within python, quite a dramatic one as well. 322 00:18:39,570 --> 00:18:41,900 Of course, [INAUDIBLE] quit immediately. 323 00:18:41,900 --> 00:18:43,930 So that's why we use direction instead. 324 00:18:43,930 --> 00:18:47,040 And incidentally this is a good example of when you would check for 325 00:18:47,040 --> 00:18:50,390 the existence of a key rather than using get with the default value. 326 00:18:50,390 --> 00:18:53,300 If we'd use get here, you remember we talked about this in the previous video, 327 00:18:53,300 --> 00:18:55,950 and wether we had a specific default value, or 328 00:18:55,950 --> 00:18:58,110 we just relied on it returning none. 329 00:18:58,110 --> 00:19:00,850 Then what we have to do is we still have to check through a ten valley before 330 00:19:00,850 --> 00:19:04,700 we can use the key and direction to retrieve the next location. 331 00:19:04,700 --> 00:19:10,810 In this case, it makes far more sense to just use the key using in before using it. 332 00:19:10,810 --> 00:19:14,080 Remember the course that the players could top anything, not just a letter for 333 00:19:14,080 --> 00:19:15,320 the valuable exits. 334 00:19:15,320 --> 00:19:18,410 Now, the only other comments to make are that we're displaying the available exists 335 00:19:18,410 --> 00:19:19,220 in an input statement. 336 00:19:19,220 --> 00:19:22,530 And we used upper on the input string, so that the player could type in upper or 337 00:19:22,530 --> 00:19:23,620 lowercase. 338 00:19:23,620 --> 00:19:25,100 This is the line here on line 24.upper. 339 00:19:25,100 --> 00:19:28,360 There's a slight problem with this program, though. 340 00:19:28,360 --> 00:19:29,270 Not with the code, but 341 00:19:29,270 --> 00:19:33,570 for us as programmers when we come to add new locations, and we're using a list 342 00:19:33,570 --> 00:19:37,750 to store the and relying on the order of the items in the list. 343 00:19:37,750 --> 00:19:42,490 Now that's fine as far as Python goes, because lists are ordered, When we start 344 00:19:42,490 --> 00:19:46,120 adding 50 or 60 locations and we don't necessarily add them in numerical order, 345 00:19:46,120 --> 00:19:49,720 we're gonna have to camp down the lines of code to make sure new entries 346 00:19:49,720 --> 00:19:51,750 are in the correct position when we build the list. 347 00:19:51,750 --> 00:19:53,820 Now, that will rapidly get tedious. 348 00:19:53,820 --> 00:19:57,260 And as well as that's gonna be a really excellent source of potential errors. 349 00:19:57,260 --> 00:20:00,330 So it would be much better if we use the location's key 350 00:20:00,330 --> 00:20:02,690 Also access its exits dictionary. 351 00:20:02,690 --> 00:20:06,250 Now there's another minor problem in that some players might type west. 352 00:20:06,250 --> 00:20:08,900 They'll put capital W and a lower case E-S-T instead of just W. 353 00:20:08,900 --> 00:20:10,880 In upper or lowercase. 354 00:20:10,880 --> 00:20:13,210 Now that doesn't matter in this case. 355 00:20:13,210 --> 00:20:17,070 But really what we should do is allow them to top the full direction 356 00:20:17,070 --> 00:20:18,800 as well as things like go west. 357 00:20:18,800 --> 00:20:21,520 Now we could achieve this by creating a dictionary containing all 358 00:20:21,520 --> 00:20:24,870 the words players may use as keys with the values perhaps being the word or 359 00:20:24,870 --> 00:20:26,640 letter that we could understand. 360 00:20:26,640 --> 00:20:28,580 Now that seems like a good idea for a challenge, so 361 00:20:28,580 --> 00:20:31,270 we're gonna do that challenge and talk about a challenge to try and 362 00:20:31,270 --> 00:20:32,790 solve that problem in the next video. 363 00:20:32,790 --> 00:20:36,370 And just one other little thing I type exists instead of exits. 364 00:20:36,370 --> 00:20:37,580 I fixed that up. 365 00:20:37,580 --> 00:20:41,480 And probably what we should do here also is we should add a space like so. 366 00:20:41,480 --> 00:20:46,100 And that's so when we run this, there's a space there between 367 00:20:46,100 --> 00:20:49,290 the end of the Available exits, and where the user can actually start typing. 368 00:20:49,290 --> 00:20:51,100 So anyway, I'm gonna end this video here now. 369 00:20:51,100 --> 00:20:53,940 In the next video we're gonna tackle those issues I've talked about 370 00:20:53,940 --> 00:20:54,980 in the form of a challenge. 371 00:20:54,980 --> 00:20:56,220 So I hope to see you in that next video.