Are dictionary keys immutable?
The hash table implementation of dictionaries uses a hash value computed from the value of the key to find the key. If the key were a mutable object, its value could change and thus its hash could change as well. Tuples are immutable and therefore can be used as dictionary keys.
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Can mutable data structure be used as key in dictionaries?
Creating a mutable type that can be modified is not prohibited, but it may not behave as you want. The requirement is that the hash of an object does not change over time and that it still compares the same (==) to its original value. Your class A meets both of these requirements, making it a valid dictionary key.
Can we use a MutableSeq object as a dictionary key?
MutableSeq Objects An important technical difference between mutable and immutable objects in Python means that you can’t use a MutableSeq object as a dictionary key, but you can use a Python String or Seq object this way. You can also get a string from a MutableSeq object as well as from a Seq object.
Can Python object keys be a dictionary?
Using a custom object as a key in a dictionary enables the use of an object of a user-defined class as a key in a dictionary.
Can a mutable object be a dictionary key?
Any object with a __hash__ method can be a dictionary key. For classes you write, this method by default returns a value based on id(self), and if equality isn’t determined by the identity of those classes, you may be surprised to use them as keys: an object can be a key in a dictionary if it is hashable.
How to create a dictionary with default immutable keys?
One was subclassing an abstract base class from the collections module and the other was subclassing dict. The rationale for actually subclassing the dictation confused me. Specifically, the discussion of the object properties of __dict__ and __slots__.
Why are all immutable objects in Python HASHABLE?
Hashability makes an object usable as both a dictionary key and a set member, because these data structures use the hash value internally. All of Python’s immutable built-in objects can be modified, whereas no mutable container (such as lists or dictionaries) is.
Why are Dict objects mutable objects in Python?
Dictionaries (dict objects) are commonly used in Python. As a quick reminder, we define them like this: Dictionaries are mutable, so we can change their content after creation. At any given time, a key in the dictionary can point to only one element: