MicroPython ‘set’ Data Type

Contents

• Introduction
• Set Definition
• Set Operators
  • Set Operations by Operator
  • Set Operations by Method
• Set Methods
• MicroPython Tutorial Links

Introduction

MicroPython is a “slim” version of Python specifically designed with a small footprint to efficiently run on memory constrained microcontrollers.

Computer languages have a built-in set of data types along with user capability to define additional custom types. MicroPython is no exception. Following are the standard or built-in MicroPython data types:

• Numeric
• Boolean
• Sequence Type
• Set
• Dictionary

Sets can also be considered a collection type

There are four collection data types in the Python programming language:

• List is a collection which is ordered and changeable.
• Tuple is a collection which is ordered and unchangeable.
• Set is a collection which is unordered, unchangeable and unindexed.
• Dictionary is a collection which is ordered^[1] and changeable.

Set Definition

A set is a mutable (can be changed) unordered collection of unique and immutable (can't be changed) objects. An important point here is that while the members of the set are immutable, the set can have members deleted and added.

Sets are defined with elements enclosed in curly brackets { } and separated by commas. A set can also be created with the set function (constructor) set(). It is important to note that the set constructor takes one and only one parameter; see example below.

Set members may be of mixed types.

Set order is arbitrary, thus there is no sort() method, unlike the list data type which can be sorted.

An item only appears once in a set regardless of the number of times it is added.

# Examples of the set data type

set_of_numbers = {1, 2, 2, 2, 3, 3, 4, 5}
print("set_of_numbers =", set_of_numbers)

set_of_apples = set('apples')
print("set_of_apples =", set_of_apples)
        

set_of_numbers = {1, 2, 3, 4, 5}
set_of_apples = {'p', 'a', 'l', 'e', 's'}
        

This example shows that regardless of the number of times the same element is added to a set, it will only appear once as a member of that set. Sets cannot be sorted so when output (e.g. with print()) the order of the elements cannot be predicted.

Set Operators

The MicroPython set type supports operations corresponding to mathematical set theory; including difference, union and intersection.

Most set operations in Python can be performed in two different ways:

• By operator
• By method

The following table shows operator versus method equivalents where defined.

These operators and methods are explained below in Table 2 and Table 3 respectively.

set declaration.
s1 = {1, 2, 3, 4, 5}

intersection operator examples.
Returns set of elements common to both sets.
s1 & {4, 5, 6, 7}  ⇒ {4, 5}

s1 & (4, 5, 6, 7)
  ⇒ error, second operand is a tuple

s1 & set((4, 5, 6, 7)) ⇒ {4, 5}

          

set declaration.
s1 = {1, 2, 3, 4, 5}

intersection method examples.
Returns set of elements common to both sets.
s1.intersection({4, 5, 6, 7}) ⇒ {4, 5}

Legal even though the parameter is a tuple.
s1.intersection((4, 5, 6, 7)) ⇒ {4, 5}

          

Set Functions

Set Methods

MicroPython also supports the following methods:

• intersection_update()
• difference_update()
• symmetric_difference_update()

These operate similarly to the methods intersection(), difference() and symmetric_difference() but modify an existing set based on the contents of a second set rather than returning a new set.

Copy the following code into the Mu Editor, save and flash to the micro:bit. Click on the REPL button to see the program's output.

# Demonstrates the use of 
# the method 'intersection_update()'.

# Removes the items that are not present
# in both sets and returns the result
# in set 'X'.

X = {'A', 'B', 'C'}
Y = {'C', 'D', 'E', 'F'}
print('\nBefore:')
print('X is', X)
print('Y is', Y)

X.intersection_update(Y)
print('\nAfter:')
print('X is', X)
print('Y is', Y)

        

Before:
X is {'C', 'A', 'B'}
Y is {'E', 'D', 'C', 'F'}

After:
X is {'C'}
Y is {'E', 'D', 'C', 'F'}