6.3.3 Mutable Set Operators and Methods

Mutable Mathematical Set Operations

In [1]:
numbers = {1, 3, 5}
In [2]:
numbers |= {2, 3, 4}
In [3]:
numbers
Out[3]:
{1, 2, 3, 4, 5}
In [4]:
numbers.update(range(10))
In [5]:
numbers
Out[5]:
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}

Other mutable set methods:

  • intersection augmented assignment &=
  • difference augmented assignment -=
  • symmetric difference augmented assignment ^=

Corresponding methods with iterable arguments:

  • intersection_update
  • difference_update
  • symmetric_difference_update

Methods for Adding and Removing Elements

  • Set method add inserts its argument if the argument is not already in the set; otherwise, the set remains unchanged.
In [6]:
numbers.add(17)
In [7]:
numbers.add(3)
In [8]:
numbers
Out[8]:
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 17}
  • Method remove removes its argument from the set—raises a KeyError if the value is not in the set.
In [9]:
numbers.remove(3)
In [10]:
numbers
Out[10]:
{0, 1, 2, 4, 5, 6, 7, 8, 9, 17}
  • Method discard also removes its argument from the set but does not cause an exception if the value is not in the set.
  • Can remove an arbitrary set element and return it with pop.
In [11]:
numbers.pop()
Out[11]:
0
In [12]:
numbers
Out[12]:
{1, 2, 4, 5, 6, 7, 8, 9, 17}
In [13]:
numbers.clear()  # empty the set
In [14]:
numbers
Out[14]:
set()

©1992–2020 by Pearson Education, Inc. All Rights Reserved. This content is based on Chapter 6 of the book Intro to Python for Computer Science and Data Science: Learning to Program with AI, Big Data and the Cloud.

DISCLAIMER: The authors and publisher of this book have used their best efforts in preparing the book. These efforts include the development, research, and testing of the theories and programs to determine their effectiveness. The authors and publisher make no warranty of any kind, expressed or implied, with regard to these programs or to the documentation contained in these books. The authors and publisher shall not be liable in any event for incidental or consequential damages in connection with, or arising out of, the furnishing, performance, or use of these programs.