org.sonar.l10n.py.rules.python.S6662.html Maven / Gradle / Ivy
This rule raises an issue when an unhashable object is used as a set member or dictionary key.
Why is this an issue?
The hash value of an object is an integer returned by its __hash__ method. Objects that are considered equal to each other (as per the
__eq__ method) should have the same hash value.
Whenever using an object as a dictionary key or inserting it into a set, the hash value of that object will be used to derive a bucket in which the
object will be inserted.
When attempting to insert an unhashable object into a set, a TypeError will be raised instead.
If an object defines a __hash__ method derived from mutable properties, no TypeError will be raised. However, having a
mutable hash value should never be done as this would prevent dictionaries and set from retrieving the object.
How to fix it
Make sure to always use hashable (and immutable) objects as dictionary keys or set members.
Code examples
Noncompliant code example
def foo():
my_list = [1,2,3]
my_set = {my_list} # Noncompliant: list is not hashable.
Compliant solution
def foo():
my_list = [1,2,3]
my_set = set(my_list) # This will insert the elements of my_list into a new set.
# OR
def foo():
my_tuple = (1,2,3)
my_set = {my_tuple} # tuples are immutable and hashable. They can be inserted into sets.
Resources
Documentation
- Python Documentation - https://docs.python.org/3/reference/datamodel.html#object.hash[object.hash]
- Python Documentation - the hash built-in function