Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 9: Real Estate Analysis App
Lecture: Mining data with loops

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0:00 All right, now you've seen all about lambdas,
0:03 and you've seen how easy the are to write to sort these data,
0:07 and that allowed us to solve two problems really easily,
0:10 if we had a sorted set of purchases, sorted form low to high by price,
0:15 we can say well the most expensive one is the last one,
0:18 and the least expensive one is the first one.
0:20 But let's ask some more interesting questions,
0:23 what is the average house price, it turns out that there is a statistics module here,
0:30 and on there we have a mean method
0:30 so we'd like to use this but we need to import that at the top, thank you PyCharm,
0:35 and we have to give it- well what does it say- data, that's kind of cool,
0:39 it even has the same name so of course we should give it data,
0:43 let's see how that works.
0:46 Hm, can't convert type purchase to numerator denominator.
0:49 Hm, ok so it looks like we need to give it an iterable set of numbers,
0:53 not an iterable set of purchases which we just made up,
0:57 so how do we get that, let's just go like this, here we'll say prices,
1:02 and we'll create that to be a list
1:05 and we'll say for purchase, let's say pur in data: prices this is really painful, right,
1:12 so we are going to go prices and we'll say append and what do we want to append,
1:16 we want to append the purchase.price.
1:18 And then we can get the average of prices so we'll say ave_price = this and let's just print,
1:24 the average home price is this is in USD and let's put a comma separator,
1:30 and a format, ave_price, let's try that.
1:35 Awesome, the average price is some number around 234,000
1:39 and let's go and round that off, there we go,
1:42 234,144 and actually that is probably truncating, but close enough for what we are after here,
1:48 this is ok but this is not so nice, right,
1:53 we created a list and we did a loop to grab the data and maybe we only want to,
1:58 maybe there is certain times we want to do a test,
2:01 so it turns out that there is actually a better way to do this,
2:05 let's go and answer other questions while using this looping construct
2:08 and then we can do something better Ha!,
2:11 it looks like I left a pass here, no harm no fell,
2:13 so it's going to look very similar to this,
2:18 so here we are going to say give me the prices,
2:21 and I want to go to there and grab each purchase and append the price,
2:25 but in this case, we want only the case where it's a purchase of a two bedroom home
2:28 so we'll say if pur.beds==2: then we'll do this,
2:33 and this will be the average price of 2 bedroom, there we go,
2:38 so let's run this again, awesome,
2:40 so the average price of all homes is 234,000 dollars
2:43 but the average price of a 2 bedroom home is a 165,000 dollars.
2:48 Maybe we also want to answer the questions like well,
2:50 how many baths does it have on average, and things like that, hm,
2:54 so this is going to be a little bit harder.
2:57 Well, it turns out this is like programming for all the programming languages
3:01 almost all of them anyway, C, C++, Java,
3:07 it does loop around here, write this procedural code,
3:08 we can actually improve upon this in 2 ways,
3:12 we can improve by using what are called list comprehensions,
3:15 which let us write this much more concisely,
3:17 and then we can actually improve upon them
3:20 using something called generator expressions,
3:23 we are going to get to both of those,
3:25 first, let's look at the challenge looking around and trying to run this code
3:28 on both Python 3 and Python 2.