Sets in Python

Enter each instruction in the Thonny shell. For each numbered instruction type

the output on the answer sheet. Submit this on Piazza by the end of class.

The set of the first four counting numbers can be created in Python by listing

the numbers in curly braces:

$N4=\{1,2,3,4\}$

A list of the first four numbers

$L4=[1,2,3,4]$

is constructed in Python with square brackets. Unlike a set, a list of numbers can

contain duplicates and the list remembers the order of the items in the list. For

example, the set of the first four counting numbers will always contain just four

numbers and the order is not remembered. The difference between a list and a set

can be seen as follows:

nums $=[4,1,4,3,2,1,4,2]$

print$($nums$)$ #$1$

N$4=$ set$($nums$)$

print$($N$4)$ #$2$

The third instruction above shows how a set can be constructed from a list. In this

case N$4$ names the set of the first four integers $($duplicates in the list are ignored$)$

and the order of the numbers in the list is forgotten.

Because the order does not matter for a set, Python displays the set elements

according to some internal representation $($which makes accessing elements of

the set easy for Python$)$ rather than the order of the items in the list from which

the set is made. For example, try to predict how the following set is presented $($by

the print instruction$)$:

nums $2=\{21,22,31,44\}$

print $(nums2)$

The fact that the printed order cannot be easily predicted corresponds to fact that

set elements are not ordered by any usable scheme.

Another example of a set is the set letters in the word 'example':

letters $={\{}^{\text{'}}{a}^{\text{'}},{?}^{\text{'}}{e}^{\text{'}},{?}^{\text{'}}{m}^{\text{'}},{?}^{\text{'}}{l}^{\text{'}},{?}^{\text{'}}{p}^{\text{'}},{?}^{\text{'}}{x}^{\text{'}}\}$

print$(letters)$

This set can be constructed with less typing as follows: