Showing Revision 10 created 05/25/2016 by Udacity Robot.

1. Title:
   Lookup - Web Development
2. Description:

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   So we've got this function, build link index, that makes our index.
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   We just wrote this together.
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   Let's use this new index function.
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   So the first thing I want to do is actually run the function and store that somewhere.
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   So we'll store that in a variable called link index=build link index.
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   Now, this isn't the best Python code.
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   Normally we wouldn't use global variables like this, but this is fine for this example.
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    One time, we're going to build this link index.
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    And now I'd like to update our link by id function
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    to use our new index.
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    Okay, so I've improved this function
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    to instead of iterating over the entire list of links,
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    to just look up the link id in the index.
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    And let's give this a test.
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    Okay, so let's call this function link by id(24).
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    We've done that a couple times. I click run.
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    Ah, and we see our link--id=24.
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    Now, what happens if we run this on a link that doesn't exist?
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    Barf!
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    Our program died because we tried to look up,
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    in a Python hashtable, an ID that doesn't exist--
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    or a key that doesn't exist.
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    So there's an easy way to fix that in Python.
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    I'll show you how to do that.
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    Instead of using these braces, we can use the function called get,
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    which Python hashtables have.
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    And what this does is it checks to see if this key is in the hashtable,
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    and if it is, that's what this function returns; otherwise, it returns none.
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    So let's give our function a test again by running this.
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    Okay, now we return none.
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    Very cool. That's what we expected.
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    And let's just make sure that our function is still working the way it worked before
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    by sending in a link that we know exists.
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    In this case, I'll do 4. Here we go.
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    So we see link id 4.
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    So now we have this function link by id
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    that uses our index.
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    So if we had a bunch of links,
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    all we'd have to do is build this index once,
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    and then we don't have to scan over it every time we do a lookup--every time we do a query.
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    Instead we can just hit the index.
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    Okay, now there's one last function I'd like you to add.
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    What I'd like you to do is implement this new function called add new link.
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    It's going to take a link--it's going to take an instance of link--as a parameter,
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    and then it needs to both add the link to our database--
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    which is this list object we've been working with links--
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    and it's also going add the links id
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    to the list--the link index.
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    Go ahead and implement this function now.