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The Set Constructor function can convert iterable data types into a set. Iterables include strings, lists, tuples, and ranges.
The Set Constructor Function
set() # new empty set
set(iterable) # new set from iterable
# examples
even_numbers = set([2, 4, 6, 8])
odd_numbers = set(range(1, 10, 2))
Some iterable types
- strings
- lists
- tuples
- ranges
Dictionaries and Sets
Passing a dictionary into the set constructor function returns a set of the dictionary keys only.
Dictionaries themselves have methods, such as .keys(), that return "dict view objects." Dict view objects are often described as "set-like."
Dictionary keys, for example, are already unique and unordered, just like sets. Because they are "set-like," dict view objects can use some set operations!
We haven't learned those operations yet (we will soon!) and performing them on dict view objects is beyond the scope of this workshop. I encourage curious minds to try experimenting with them after completing this workshop :)
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We have just learned how to
make sets with literal syntax.
0:01
We experimented with making
Singleton sets with one element,
0:05
and sets with many elements.
0:11
We learned that sets can
only contain immutable data.
0:13
Let's try using what we've learned so
far to make an empty set.
0:17
On line one here,
I'll declare a new variable empty_set.
0:23
And I'll assign it to an empty set
literal, which is a pair of curly braces.
0:28
Then I'll print out my empty set and
let's see what we get.
0:36
So my return value here is
a pair of curly braces, but
0:44
I wanna make super sure that
this is actually a set.
0:48
So what I'll do is,
I'll use the type function.
0:52
So I can see the return value of
the type that my empty set actually is.
0:59
I'll run my script again.
1:05
And this is actually a dictionary, so we
can't make an empty set with curly braces.
1:09
To make an empty set, we actually have
to use the set constructor function.
1:16
So I'll go all the way up
here to line one again and
1:21
I'll reassign my variable to use
this set constructor function,
1:25
which is just the word set
followed by a pair of parentheses.
1:30
Now I'll run my script again.
1:35
And there's two things to notice here.
1:40
First, when I print out
a line two my empty set,
1:42
the return value is exactly the same
as my set constructor function.
1:47
If you ever see this set
function as a return value,
1:53
it means that that's an empty set.
1:58
The type returns the class set.
2:01
So I know for sure that this is a set.
2:06
I know two ways that this is a set.
2:09
The set constructor function can also
take any iterable as an argument.
2:14
So right now we've just made an empty set,
2:19
now we're going to make
a set with many elements.
2:23
We're going to pass in an iterable.
2:27
And recall that an iterable is the type
that you can use in a for loop.
2:29
I'm gonna use my favorite data type
that's an iterable, which is a string.
2:34
I have a sentence here,
My favorite data type
2:39
is the string, exclamation point.
2:43
Really excited about it.
2:47
And now I can use the set
function to convert my
2:50
string into a set of letters,
letters equals set.
2:54
And I'll pass in my sentence.
2:59
Now let's print out my letters and
see what is happening here.
3:03
What are we gonna get?
3:09
All right, so what happened here?
3:18
The set function went through
every letter of my sentence,
3:22
it looped through each element of
the string, which is a character.
3:26
And then it added in every letter,
every character into the set,
3:31
but it also removed the duplicates.
3:38
I wanna prove this to you, and
I can show you two ways, right?
3:42
The first way is by visually comparing.
3:45
I see here that there's one space
3:48
character that is a member
of this letter set.
3:51
And then my sentence string there is one,
two, three, four, five, and six spaces.
3:56
So only one space got added in.
4:03
And I can prove this to
programmatically as well by comparing
4:07
the length of my sentence versus
the length of my letter set.
4:12
So let's do that.
4:17
Len letters less than len sentence.
4:19
And if this is true, then we'll know that
4:26
some of the elements of the sentence
were not added into the letter set.
4:31
So I'll run this again and let me comment
out my older print statements here.
4:39
So it's true! There are less
members in the letter
4:49
set than there are elements
in the sentence.
4:54
Let's try another example
with real-world objects.
5:02
Colors are a good example of data that
we can collect into a set because they
5:12
are distinctly unique and it doesn't
usually matter what order we collect them.
5:17
So let's make a list of primary colors.
5:23
We'll have red, yellow and blue.
5:29
I can convert this list into a set
with the set constructor function
5:39
similarly to how the str and int functions
that convert one data type to another.
5:44
And now if I print out my primary colors,
5:57
I can see that I have a set.
6:06
And remember, if the order of your
colors are different than mine,
6:08
it's totally okay, order does not matter.
6:13
I'll run my script again to
show you that it comes up
6:17
differently when I run
it another two times.
6:21
So we've just used a string, a list.
6:25
How about we pass in a tuple
to the set function?
6:30
A tuple is also iterable.
6:33
This time we'll have secondary colors.
6:35
We'll have tuple,
6:41
which is parentheses and
6:45
we'll call this one with orange,
6:49
purple, and green.
6:56
Close this parentheses, there we go.
6:59
And we will do this the same way.
7:03
So I've got my tuple of
secondary colors and
7:13
passing in the tuple to my
set constructor function.
7:17
To convert it from a tuple into a set,
I'll print out my secondary colors.
7:22
Orange, purple, or green, nice.
7:35
That one came in the same order as I
typed it out, but if I run it again,
7:38
it will come out in a different order,
so non-deterministic.
7:42
Ranges can also be passed to
the set function to quickly
7:46
build sets of integers.
7:51
Odds, set, range and
7:53
I'll go from 1 to 10 stepping by 2 and
7:57
I can also do the same for evens.
8:04
This time I'll start at number 2,
we'll go up to 11 stepping by 2.
8:10
And let's print these out.
8:17
Print(odds), print(evens).
8:19
I'll run my script again.
8:29
There we go.
8:31
I've mentioned that the return values
of sets are non-deterministic, but
8:33
sometimes they always
appear in the same order.
8:42
The reason for
this has to do with the built-in hashable
8:48
attribute that many
Python objects do have.
8:53
You saw this in the last video when I
tried to print out my Boolean set and
8:58
it didn't change the order
like the other ones.
9:04
So some of the built-in
data types like integers or
9:07
booleans or the none type,
they will appear in the same order,
9:12
but for other things like strings,
tuples, mixed data types,
9:17
the order will come out
to be non deterministic.
9:23
In the last video, I demonstrated how set
literals cannot contain a dictionary.
9:27
A dictionary can be passed to
the set constructor function, but
9:34
the behavior is not
quite what you'd expect.
9:39
I'll show you.
9:42
First, I'll make
a dictionary of groceries.
9:45
We'll have milk, and
1 milk, and some bread.
9:51
We'll have 2 breads.
9:56
Now when I pass my groceries dictionary
to the set constructor function and
10:02
I print out that result,
let's check what the return value is.
10:09
Bread and milk, my grocery set just
has the keys of bread and milk.
10:19
Since dictionaries are key value pairs,
10:25
the set function will only make
a set of the dictionary keys.
10:28
Check out my teacher's notes for
more details about dictionaries and sets.
10:33
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