This course will introduce students to the basics of the Structured Query Language (SQL) as well as basic database design for storing data as part of a multi-step data gathering, analysis, and processing effort. The course will use SQLite3 as its database. We will also build web crawlers and multi-step data gathering and visualization processes. We will use the D3.js library to do basic data visualization. This course will cover Chapters 14-15 of the book “Python for Everybody”. To succeed in this course, you should be familiar with the material covered in Chapters 1-13 of the textbook and the first three courses in this specialization. This course covers Python 3.
Worked Example: Twspider.py (Chapter 15)
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來自 University of Michigan 的課程
Using Databases with Python
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從本節課中
Basic Structured Query Language
We learn the four core CRUD operations (Create, Read, Update, and Delete) to manage data stored in a database.
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Charles SeveranceProfessor
School of Information
Hello everybody, and welcome to Python for Everybody.
We're going to do some code walk-through.
If you want to follow through with the code,
you can download the sample code from Python for Everybody.
So, the code that we're going to play with is
the Twitter spider code that is both talking
to the Twitter API and talking to the database.
So, what we're going to be doing is we are going to run
code that's going to hit the Twitter API much like we did in a previous chapter,
and we're going to retrieve the data,
but we're going to remember the data.
So, we don't have to retrieve it again.
So, we're going to keep track of people's friends.
What we're doing here is illicitly pulling down slowly,
but surely based subject to our rate limit.
We're pulling down who our friends are.
So, let's take a look. We're going to use urllib and urllib.error,
the Twitter_URL, which was code that augments my url to do all the OAuth calculation.
We're going to get json data back.
We're going to make a database and we have to import SQL because of
the way Python doesn't trust any certificates no matter how good they are.
So, this is our URL to talk to the Twitter API.
We're going to make a database.
Again, the way SQLite works is as if this spider.sqlite doesn't exist, it creates it.
We get ourselves a cursor and we're going to do a create table,
this if not exists some SQLs,
but sqlite3 does this.
Create table if it doesn't exist.
We want to start this over and over unlike the tracks example.
I want to start this over and over,
and not lose data.
This is a spidering process and we'll see a lot of these.
We want a restartable process where we use a database.
So, if we're starting with nothing and there's no file,
spider.sqlite, it creates this table.
It's the name of the person whether we retrieved or not
and how many friends this person has that we know of in our database.
Now, this little bit is to deal with the SSL certificate errors.
The certificates are totally fine,
but Python doesn't trust any certificates by default,
which is frustrating, but whatever.
So here, we're going to have a loop.
We're going to ask for Twitter account.
We have to type quit to quit.
If we hit Enter in this case,
we're going to actually read from the database on
unretrieved Twitter person and then grab all that person's friends.
9Okay. So then, if we're going to do a fetchone,
get one, and that's going to get the name of the first person,
the sub zero, if we add more things than name here,
sub zero was the first of those.
Fetchone means get one row from the database and
sub zero means the first column of that first row.
If this fails, then we retrieved all the Twitter accounts.
So, we're going to augment this Twitter_URL using this mix.
You can look at the twurl.py code.
This basically requires the hidden.py file,
which has your keys and secrets in it.
You've got to get hidden.py updated.
I've got it updated, but I'm not going to show you
because it has my keys and secrets in it.
So, we're only going to take the first five,
which means we're not going to find friends of friends of friends.
It's only at most five recent ones.
We could run this with a much higher number,
so we have more than one friend.
We'll show the URL while we retrieve it.
We will do our URL open.
We'll do a read, and then we'll do a decode to make sure that this UTF,
this will give us data in UTF eight,
and then decode will give us data in unicode,
which is what we need inside of Python.
We will ask for the headers from the connection.
We'll say, "Give me the headers.
Give me a dictionary of the headers."
The x-rate-limit-remaining header from the Twitter API tells us
when we're going to be told we can't use
this API anymore because this is one of those things,
and then we're going to parse, and load the data that we got from Twitter,
and get a, I think it's a list.
Yes, it's a list, and then we could dump this if you want in here as you can undo that.
Then, what we're going to do is we just
retrieved this person screen name and their friends.
So, the first thing we want to do is update
the database and change the retrieved from zero to one.
That's because we're going to use this to know about unretrieved.
So, retrieved being one means we've already retrieved it and we did retrieve it.
So, for that account, we've retrieved it.
Then, what we're going to do is we're going to parse that.
So, this is similar to the Twitter code we did previously in the web services chapter.
We're going to go through all the users.
We're going to find their screen name.
We're going to print the screen name out, okay?
Then, what we're going to do is see if, let's see,
so we're going through all the users who are the friends of this person,
and we're going to say, "Okay.
Let's select the friends from Twitter where the name is the friend person."
What we're going to do is if we're going to do a cur.fetchone of this Twitter,
the name of the friends,
this is the friend's screen name,
so we're going to say, "Okay.
If we get this,
we're going to get that friend's screen name and we're going to get
how many friends this particular screen name has.
If we find a URL,
if we find it in there,
we're going to do an update statement,
and add one to their friend count,
how many friends they have,
and then keep track."
This count here is not in the database.
It's just so I can print it out at the end.
If there is no record for this particular friend,
we're going to insert them into a new,
and we're going to say, "Here's the new person that we just saw."
That's their name. We're going to set retrieved to
zero and we're going to say that they have one friend.
We're going to commit the transaction and then we're going to close this at the end.
So, let's go ahead and run this.
The first time it's going to create an empty database.
So, I'm going to say, python3 twspider.
So, ls *sqlite, nothing there.
Python3, oops, that's because I removed it.
Python3 twspider.py.
Okay. So, I'm going to start with a Twitter account, drchuck.
So, it's doing this retrieval. Don't worry.
Showing the token and the signature is not
dangerous because you don't want the keys or the token,
the secrets and the token secrets.
So, don't get all too worried.
So, I have 11 calls left.
So, I got to hope this all works.
One of my friends is Stephanie Teasley.
I do these in reverse order.
So, let's grab Stephanie and ask for Stephanie's friends.
So now, we just retrieved Stephanie's friends.
Here are Stephanie's most recent friends,
and then I can just hit Enter,
and it will randomly pick.
Let's see if I can in the database.
Let's open this up, File, Open Database.
Hope I don't lock myself.
Sometimes it's a little scary when you look at the database and you're just checking.
So, this is what my database looks like.
We retrieved Stephanie and she has,
this is how many people.
So, these are the friends of Stephanie and me.
I'm not in there. So, we've retrieved Stephanie, which was a friend.
So, let's go grab, I don't know.
Let's grab Tim McKay and get that one.
Remaining 10. I don't have too many of these, Tim McKay.
So, there we go.
Remaining nine.
So, if I do a refresh on this,
then you see I've got some more folks.
If I hit Enter here,
it'll pick one randomly based on the retrieved being zero.
So, it won't pick Stephanie or Tim because there's zero,
but we have lots of other folks to pick randomly.
We'll hit Enter. Who did it pick?
It picked screen named liveedutv,
which is ironic because I'm recording this on LiveEdu.tv right now.
So, we can keep hitting refresh in the way we go.
So, I'm going to stop now because I only have eight remaining.
So, I'm going to type quit.
So, we'll see how that works.
So that's how it works.
Now, remember that you've got to edit the
hidden.py file to make this work because we are talking to the Twitter API.
If you don't edit that file, it won't work for you.
So, I hope you find this useful. Cheers.
