Difference between revisions of "Python-3.4.3/C3/Sets-in-Python/English"

Objectives

• Create sets from lists
• Perform union, intersection and symmetric difference operations
• Check if a set is a subset of other and
• Understand various similarities with lists

System Specifications

• Ubuntu Linux 16.04 operating system
• Python 3.4.3 and
• IPython 5.1.0

Pre-requisites

• run basic Python commands on the ipython console and
• use lists

If not, see the relevant Python tutorials on this website.

Sets are unordered collections of unique elements.

The set itself is mutable.

We can add or remove items from it.

Open the terminal.

From here onwards, remember to press the Enter key after typing every command on the terminal.

a_list = [1, 2, 1, 4, 5, 6, 2]

a = set(a_list)

a

Highlight the output

Type,

a underscore list is equal to inside square brackets 1 comma 2 comma 1 comma 4 comma 5 comma 6 comma 2

Type, a is equal to set inside brackets a underscore list

Then type, a

We can see that duplicates are removed and the set contains only unique elements.

b = {1, 2, 1, 4, 5, 6, 2}

b

Type,

b is equal to inside curly braces 1 comma 2 comma 1 comma 4 comma 5 comma 6 comma 2

Type, b

As before, we see that the set contains only unique elements.

Show text d = {}

c is equal to set open and close brackets

Note that d is equal to open and close curly braces creates an empty dictionary, not an empty set.

b_list = [[1], 2, 1, 6, 2]

b = set(b_list)

Highlight TypeError

But cannot contain mutable elements such as lists or dictionaries.

Type,

b underscore list is equal to inside square brackets again inside square brackets 1 comma 2 comma 1 comma 6 comma 2

Now type, b is equal to set inside brackets b underscore list

As you can see, it gives a TypeError.

f = set([1, 2, 3, 5, 8])

p = set([2, 3, 5, 7,11,13])

For this, we will first create a pair of sets.

Type the sets as shown.

Here, f is the set of fibonacci numbers from 1 to 10.

p is the set of prime numbers from 1 to 15.

f.add(13)

f

First we will add an element to a set by using add method.

Type,

f dot add inside brackets 13

Now type, f

As you can see, 13 is added to the set f.

f.add(13)

f

Type,

f dot add inside brackets 13

Type, f

As you can see, 13 is not added this time.

p.remove(13)

p

Type,

p dot remove inside brackets 13

Now type, p

As you can see, 13 is removed from the set p.

p.remove(18)

Type,

p dot remove inside brackets 18

KeyError is raised since element 18 is not present in p.

f | p

f.union(p)

Type,

f pipe p

Or type, f dot union inside brackets p

It gave the union of f and p

f & p

f.intersection(p)

Type,

f ampersand p

Or type, f dot intersection inside brackets p

It gave the intersection of f and p.

f - p

f.difference(p)

f minus p

Or type, f dot difference inside brackets p

It gave all the elements that are in f but not in p.

f ^ p

f.symmetric_difference(p)

f caret p

Or type, f dot symmetric underscore difference inside brackets p

It gives all the elements in f union p but not in f intersection p.

In mathematical terms, it gives the symmetric difference.

<<PAUSE>>

a = set([1, 2, 3, 4])

b = set([1, 2])

b <= a

b.issubset(a)

Type,

a is equal to set inside brackets inside square brackets 1 comma 2 comma 3 comma 4

Type, b is equal to set inside brackets inside square brackets 1 comma 2

Now type, b less than or equal to a

Or type, b dot issubset inside brackets a

It gives a True since b is a subset of a.

b >= a

b.issuperset(a)

Type,

b greater than or equal to a

Or type, b dot issuperset inside brackets a

We get False since b is not a superset of a.

a <= a

a >= a

Type,

a less than or equal to a

a greater than or equal to a

It gives True in both cases since a is a superset and subset of itself.

for x in a:

print(x)

Type,

for x in a colon

print inside brackets x

The items from the set will not appear in any specific order.

len(a)

Type,

len inside brackets a

It shows 4.

1 in a

7 in a

1 in a

7 in a

It prints True and False respectively

Hence, slicing and striding are not valid on sets.

Try this exercise and then resume the video.

Exercise 1

marks = [20, 23, 22, 23, 20, 21, 23]

marks_set = set(marks)

for num in marks_set:

marks.remove(num)

marks is equal to inside square brackets 20 comma 23 comma 22 comma 23 comma 20 comma 21 comma 23

marks underscore set is equal to set inside brackets marks

for num in marks underscore set colon

marks dot remove inside brackets num

remove method only removes the first occurrence of an element from the list.

duplicates = set(marks)

duplicates

duplicates is equal to set inside bracket marks

Now type, duplicates

We now have duplicate marks in the set duplicates.

Hence, we have obtained our required solution.

Summary slide

In this tutorial, we have learnt to,

• Make sets from lists or by using curly braces
• Perform union, intersection and symmetric difference operations
• Check if a set is a subset of other using the less than or equal to operator
• Understand the various similarities with lists like length and containership

Evaluation

1. If a is assigned as follows, what is set of a
2. Given odd and squares as shown. How do you find the symmetric difference of these two sets?
3. If a is a set, how do you check if a variable b exists in a?

Solutions

1. set of a will have all the common elements in the list a, that is 1 comma 2 comma 3 comma 5 comma 8.
2. To find the symmetric difference between two sets, we use the operator caret. So we can type odd caret squares
3. To check the containership, we type, b in a

Acknowledgement

For more details, visit this website.

Thank You

Thanks for watching.