Python/C3/Sets/English

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Visual Cue Narration
Show Slide 1

Containing title, name of the production team along with the logo of MHRD

Hello friends and welcome to the tutorial on 'Sets'.
Show Slide 2

Learning objectives

At the end of this tutorial, you will be able to,
  1. Create sets from lists.
  2. Perform union, intersection and symmetric difference operations.
  3. Check if a set is a subset of other.
  4. Understand various similarities with lists like length and containership.


Show Slide 3

Pre-requisite slide

Before beginning this tutorial,we would suggest you to complete the tutorial on "Getting started with Lists"
ipython Now, What are sets? Sets are data structures which contain unique elements. In other words, duplicates are not allowed in sets.

First let us invoke our ipython interpreter

a_list = [1, 2, 1, 4, 5, 6, 2]
a = set(a_list)
a
Lets look at how to input sets. type
f10 = set([1, 2, 3, 5, 8])
p10 = set([2, 3, 5, 7])
We can see that duplicates are removed and the set contains only unique elements. Now let us perform some operations on sets. For this, we shall first create a pair of sets
p10 f10 is the set of fibonacci numbers from 1 to 10. p10 is the set of prime numbers from 1 to 10.

Various operations can be performed on sets. For example, The | (pipe) character stands for union

f10 & p10 It gave the union of f10 and p10

The '&' character stands for intersection.

f10 - p10 It gave the intersection of f10 and p10

similarly,f10 - p10 gives all the elements that are in f10 but not in p10

f10 ^ p10 and f10 ^ p10 gives all the elements in f10 union p10 but not in f10 intersection p10.
b = set([1, 2])
b < f10
In mathematical terms, it gives the symmetric difference.

Sets also support checking of subsets.

f10 < f10 It gives a True since b is a proper subset of f10. Similarly,
f10 <= f10 It gives a False since f10 is not a proper subset. hence the right way to do would be
for i in f10:
    print i,
we get a True since every set is a subset of itself.

Sets can be iterated upon just like lists and tuples.

len(f10) It prints the elements of f10.

The length and containership check on sets is similar as in lists and tuples.

1 in f10
2 in f10
It shows 5. And
prints True and False respectively

The order in which elements are organized in a set is not to be relied upon, since sets do not support indexing. Hence, slicing and striding are not valid on sets.

Pause the video here, try out the following exercise and resume the video.

Show Slide 4

Assignment 1

Given a list of marks, marks = [20, 23, 22, 23, 20, 21, 23]

list all the duplicates

Continue from paused state Switch to the terminal Duplicates marks are the marks left out when we remove each element of the list exactly one time.
marks = [20, 23, 22, 23, 20, 21, 23]
marks_set = set(marks)
for mark in marks_set:
    marks.remove(mark)
duplicates = set(marks)
duplicates
We are now left with only duplicates in the list marks Hence,
We obtained our required solution
Show Slide 5

Summary slide

This brings us to the end of the tutorial. In this tutorial, we have learnt to,
  1. Make sets from lists.
  2. Perform union, intersection and symmetric difference operations. by using the operators |, & and ^ respectively.
  3. Check if a set is a subset of other using the < and <= operators.
  4. Understand various similarities with lists like length and containership.


Show Slide 6

Self assessment questions slide

Here are some self assessment questions for you to solve
  1. If a = [1, 1, 2, 3, 3, 5, 5, 8]. What is set(a)
    • set([1, 1, 2, 3, 3, 5, 5, 8])
    • set([1, 2, 3, 5, 8])
    • set([1, 2, 3, 3, 5, 5])
    • Error
  1. odd = set([1, 3, 5, 7, 9]) and squares = set([1, 4, 9, 16]).
    How do you find the symmetric difference of these two sets?
  2. a is a set. how do you check if a variable b exists in a?


Show Slide 7

Solution of self assessment questions on slide

And the answers,
  1. set(a) will have all the common elements in the list a, that is set([1, 2, 3, 5, 8]).
  2. To find the symmetric difference between two sets, we use the operator ^.

Enumerated list ends without a blank line; unexpected unindent.

odd ^ squares

3. To check the containership, we say,

b in a
Show Slide 8

Acknowledgment slide

Hope you have enjoyed this tutorial and found it useful. Thank you!

Contributors and Content Editors

Chandrika