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

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

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   So far, we've been doing--in our Phyton IDE--
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   we've been doing what are called sequential scans.
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   And a sequential scan is where you have a list of something.
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   In our case, links.
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   We have this list of links
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   that have these IDs--link 1, link 2, link 3.
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   And we've been doing things like find the link with the ID of 2,
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    so in which case we write a loop to
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    go over the list and find the one who has ID 2.
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    Or you just eyeball it by hand
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    and answer your quiz just by writing in the answer by hand,
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    which is actually totally fine because you went through the same process.
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    You had to look through this whole list of links by hand.
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    Now, that works fine if you have 25 links,
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    but if you have a million links or a billion links,
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    iterating over that entire list is going to take some time,
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    and we want to make our websites fast,
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    or at least reasonably responsive.
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    So that's going to be troublesome.
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    So I'd like to introduce you to a new concept called Indexes.
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    And index is just like an index in a book.
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    They make lookups faster.
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    One index you're probably familiar with already is the hashtable.
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    So in Python you can have a dictionary
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    that looks something like this--
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    that is a mapping--a key--to a value.
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    Let's assign this to a variable.
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    We'll call this just index.
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    Now, you can do very fast lookups in your code
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    by writing something that looks like this,
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    which we'll refer to the index key 2 of this hash table.
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    And when you do a hashtable lookup--
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    you learned this in CS 101--
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    we hash this value, we find it in the hashtable,
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    and then we return the key--
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    or we return the value.
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    We don't have to scan over every element in the list and see if it matches our constraint.
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    We can jump immediately to that element.
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    And that makes queries run much faster.
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    Okay, so let's play around with this in the IDE a little bit
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    and see what we can do.