PythonDictionaries and sets
set.
Adds an element to a set. If the element is already there, the set doesn't change.
- Returns
None(the set changes in place).- Changes the original
- Yes
Example
#Python
visited = {"lesson_1", "lesson_2"}
visited.add("lesson_3")
visited.add("lesson_1")
print(len(visited))
print(sorted(visited))Resultsaved result, you can check it
3
['lesson_1', 'lesson_2', 'lesson_3']
Definition and usage
#The add(element) method inserts a single element into a set. A set only stores unique values, so adding an element that is already there changes nothing and raises no error.
Set elements must be hashable, meaning immutable in practice: numbers, strings, tuples. Trying to add a list or a dictionary raises a TypeError. Add several elements at once with the update() method.
The method changes the set in place and returns None. Sets have no order, so a new element does not land "at the end" the way it would in a list. For display, it is convenient to sort the set with the sorted() function.
Syntax
#Syntax
set.add(element)Parameters
#element
a hashable value
The element to add.
More examples
#Python
logins = ["emma", "jack", "emma", "mia", "jack"]
seen = set()
duplicates = set()
for login in logins:
if login in seen:
duplicates.add(login)
seen.add(login)
print(sorted(duplicates))Resultsaved result, you can check it
['emma', 'jack']
Python
tags = set()
tags.add(("python", 3))
print(tags)
try:
tags.add(["python", 3])
except TypeError:
print("A list cannot be a set element")Resultsaved result, you can check it
{('python', 3)}
A list cannot be a set element
Good practices
#- A set like
seenis great for remembering what you have already encountered. Checkingx in seenis fast no matter how many elements there are. - Create an empty set only with
set(), because{}means an empty dictionary.
Related entries
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