#100DaysOfCode in Python Transcripts
Chapter: Days 4-6: Collections module
Lecture: Concepts: what did we learn
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Next up are deques.
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deques are stacks and queues.
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They're useful if you want to insert and append
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on both sides of the sequence.
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In this section, I will compare them to lists.
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I mean, lists are your best friends.
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You will use them everywhere.
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They're easy to use and for 80% of your use cases,
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or maybe 90%, they're just adequate.
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But lists come with a downside which if you have
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to move items around, they get less performant.
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And in this exercise, I will create a list and a deque
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of ten million ints and a function to do random inserts
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and deletes and then we're going to use timeit,
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to see how they perform.
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So let's create the two sequences.
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First I want a list.
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I can just use the range.
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Let me the get the zeros right.
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One, two, three, one, two three.
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That's ten million.
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And let's make a deque.
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You create that big deque.
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Range, one, two, three, one, two three.
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Next, we create an insert and delete function
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that takes a sequence...
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and we do, for...
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Underscore...
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In braces..
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Index equals random...
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Choice.
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And a random choice takes a sequence
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and just randomly chooses one item.
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I store that into index
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and I remove it.
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So that index is like a random location in the sequence.
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I'm going to remove the item that's at that index.
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And I'm going to do an insert of index
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at index and I'm just going to insert
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the same value of index, doesn't really matter.
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I'm going to use timeit to time this function
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for both the list and the deque.
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Here we have the timeit module.
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And we're going to call it with insert and delete
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on the list, and the list we defined here above.
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You can see this took a little bit.
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And now let's do the same for the deque
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which we defined here.
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And although it seems to take a little bit as well.
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Here we're talking about milliseconds
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and here we're talking about microseconds.
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Here it also run like 10,000 loops.
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This one was slower so it reduced to one loop.
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So deque performs at a fraction of the list
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and that's because inserting and removing
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at both sides of the sequence are more efficient
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in a deque than a list.
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A list has to move all the items around
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and that's expensive.
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I encourage you to look at the docs because there are a few
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other data types that are interesting
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and you can read about ChainMap, for example.
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An OrderedDict is another good data type to know about.
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Although I think in Python 3.6,
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dicts are becoming ordered by default.
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That concludes day one.
