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Sets can only contain immutable data types. Immutable means the data cannot be changed after it is created, such as strings, integers, and floats.
What are some immutable types?
- string
- integer
- float
- True
- False
- None
Can I put a tuple in a set?
Tuples are also an immutable type! A tuple can be in a set if and only if the elements of the tuple are also immutable. Making a set with a tuple that contains mutable types will raise a TypeError.
Why does the TypeError say unhashable type?
Unhashable means Mutable. Our TypeErrors were telling us that lists, dictionaries, and sets are mutable.
Hashable means Immutable. A hashable type can be a member of a set or a dictionary key. Hashable objects are why sets and dictionaries are so fast at "lookup" operations.
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Let's now talk about what
exactly can go inside of a set.
0:00
So far, we've been making sets with
strings, integers, and floats.
0:06
Elements of a set can be
of mixed types of data.
0:11
Let's make a new set
literal to demonstrate.
0:16
First, I'll comment out my
other print statements.
0:19
And we'll make a new set literal.
0:26
This one I'm going to call twos.
0:29
And we're gonna have different
types of twos in here.
0:31
First, we'll have the string two,
the integer 2.
0:34
How about a float 2.22 and
0:39
then a tuple with the word dos,
0:43
which is Spanish for the word two.
0:48
All right, and let's print out my twos.
0:53
Go into my terminal and
run my script again.
1:00
2, two, dos, Spanish, 2.2,
notice how the return value is in
1:06
a different order than the set
literal that I typed out.
1:11
Remember that sets
are unordered collections.
1:16
So if your set is in a different
order than mine, that's okay.
1:19
The order does not matter.
1:24
The way that it shows up differently
than how we type it here,
1:28
sometimes you'll hear sets
referred to as non-deterministic.
1:32
The order of sets are non-deterministic,
which means that it can be kind of random,
1:37
but since they're unordered, don't panic.
1:42
Since they're unordered,
it's totally okay.
1:45
Watch if I run my script again,
it comes out into a different order and
1:48
I run it again,
it comes out into a different order.
1:52
And it's still the exact same set.
1:56
So don't panic if it looks a little
bit different, totally okay.
1:59
So, we see here that elements of
a set can be of mixed types of data,
2:04
right, integer, float, string, tuple.
2:10
All of these types have
something in common though,
2:14
these are all immutable data types,
IMMUTABLE.
2:19
Sets can only contain
immutable data types.
2:24
This is similar to Python dictionaries,
2:27
where the keys of the dictionary
can also be only immutable types.
2:30
Immutable means that the data cannot
be changed after being created.
2:36
Strings, integers, floats, and
tuples are immutable types.
2:42
And there are more immutable types too.
2:47
I can make a set with boolean values.
2:50
Booleans with the values True and False.
2:54
And we'll print that out,
In our script down here in the terminal.
3:04
I can see if the order's
non-deterministic... false, true,
3:12
false, true, false, true.
3:17
[LAUGH] That one doesn't seem to be
letting up into a different order, but
3:19
that's okay.
3:24
Now, what else can I do?
3:27
Some other immutable types are Python's
3:31
None type, which is just None.
3:37
And I can print that out as well.
Brilliant.
3:42
Lists, dictionaries and
other sets cannot be elements of a set.
3:48
Because those are MUTABLE types,
the contents of a list, a dictionary, or
3:55
a set can be manipulated and
updated at any time.
4:00
Watch what happens when I try to
put a MUTABLE type into a set.
4:04
So this time,
I'll comment out my print statements.
4:09
And, I'll try to make a set
with one element of a list.
4:14
So I'll open up my curly braces, and
then inside I'll use my square brackets.
4:20
And I'll make a list of one,
two, and three.
4:25
So right here, I can print this out.
4:29
And, what will happen
when I print this out?
4:38
I already said that sets can
only contain immutable values.
4:42
I tried to make a set with
a mutable value, a list.
4:47
And, right here I've got an error,
4:51
a TypeError that says that
this is an unhashable type,
4:55
the list, unhashable type.
5:01
We can see the same error message if
we use any other mutable types of
5:04
data like a dictionary.
5:09
So I'll make a dictionary here.
5:11
Hello, world.
5:13
And, I get the same TypeError,
it's an unhashable type,
5:19
the dictionary is unhashable.
5:24
And I can do the same with a set.
5:27
Hello, sets, a set within a set,
5:32
gives me an error, an unhashable type.
5:37
You can check out my teacher's notes to
learn more about what unhashable means.
5:44
But for now, all you got to know is that
it means you can't use that data type,
5:49
you've got to use an immutable data type.
5:55
So a string, an integer,
a float, or tuple.
5:59
And, if you're using a tuple, the elements
of the tuple must also be immutable.
6:05
I'll demonstrate that here.
6:13
So, how about I'll run
a tuple with a list.
6:14
Just an empty list in there.
6:23
I know this looks really funny but
this is going to be interpreted.
6:25
And that will give me an error that I have
an unhashable type in my set right there.
6:30
So far, we've gone over making
sets with literal syntax.
6:37
Curly braces wrapped around
immutable data, like integers,
6:41
strings, floats, tuples,
Booleans, and the None data type.
6:46
Inside of the curly braces, each element,
or member, are separated by commas.
6:52
We've made singleton sets with only
one member and sets with many members.
7:01
We've explored the two
basic properties of sets.
7:08
Sets are unordered collections and
sets have unique elements.
7:12
And we've observed some behaviors of sets.
7:18
Sets will remove duplicate
data from itself.
7:21
Making literals is a great
way to learn a new data type.
7:27
In the next video,
7:31
I'll show you another way to create
sets with the set constructor function.
7:32
Then we'll explore a little
bit more about deduplication,
7:38
removing duplicates from a set.
7:42
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