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The First Property: No Order
3:58The syntax for creating a Set Literal is similar to creating a List! Curly braces wrap around elements separated by commas.
We've just had a brief
introduction to Python Sets,
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an unordered collection
of unique elements.
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So, how do we make a set in Python?
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What is the syntax?
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I'll show you.
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Let's start an interactive
Python session in the terminal.
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On the command line,
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I'll type in Python and keep in mind
that you may need Python3 on a Mac.
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Press return, and we can get
started with making our first set.
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I'll declare a variable, my_first_set, and
we make a set literal with curly braces,
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and I'll use a string for
my first element.
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We'll say, "Hello sets!",
close the curly brace and hit return.
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And I can see if I call my first set,
that variable I just declared,
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I get a set returned,
my set literal with curly braces.
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I can double-check that this is
actually a set by using the type
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function on my_first_set, and I can see
that it is of the class set, perfect.
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Since a set is a collection, I can also
use the built-in length function, len.
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And when I hit return,
I get 1. This function returns
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1 because the set contains
only one element.
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A set containing exactly one element
is also known as a singleton set.
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Let's go over the two
basic properties of sets.
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Remember that a set is an unordered
collection of unique elements,
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and the first property is that the order
of the elements does not matter.
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I'll show you what that means.
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So, on a new line,
I'll make a couple of sets.
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First I'll make a start
with some integers 1, 2, and
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3, and I'll use a double equal
sign to compare it to another set,
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the same numbers but
in a different order, 3, 2, and 1.
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And with this expression here,
I'm comparing them and
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I want to print out the result
of this comparison, so
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I'll throw this into a print statement.
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And now I can run my script and
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what I want to see is true, that's right.
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Python evaluated these two sets, and
it considers both of them to be equal.
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They are of the same length, and
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they contain the exact same
elements as each other.
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Even though they're not in order,
sets are not a sequence, so
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the order does not matter.
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That's quite different than how
it works with say lists, right,
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where the order does matter.
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And I can show you what
that looks like here.
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So order does not matter with sets,
but it does matter with a list.
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So I'll edit the text here to change out
my curly braces for square brackets
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And I'll run my script again.
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So this time, what I hope to see is false,
right, there's false.
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So when I compare two lists
with the same length,
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the same elements in a different order,
it returns false.
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But if I have two sets,
same length, same elements,
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different order, it will return true.
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We'll run the script one more time,
so you can see both results, so
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I said first it's true and then false.
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True, false, excellent.
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So that's the first property,
the order does not matter.
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