I'm confused on what an immutable type is. I know the float
object is considered to be immutable, with this type of example from my book:
class RoundFloat(float):
def __new__(cls, val):
return float.__new__(cls, round(val, 2))
Is this considered to be immutable because of the class structure / hierarchy?, meaning float
is at the top of the class and is its own method call. Similar to this type of example (even though my book says dict
is mutable):
class SortedKeyDict(dict):
def __new__(cls, val):
return dict.__new__(cls, val.clear())
Whereas something mutable has methods inside the class, with this type of example:
class SortedKeyDict_a(dict):
def example(self):
return self.keys()
Also, for the last class(SortedKeyDict_a)
, if I pass this type of set to it:
d = (('zheng-cai', 67), ('hui-jun', 68),('xin-yi', 2))
without calling the example
method, it returns a dictionary. The SortedKeyDict
with __new__
flags it as an error. I tried passing integers to the RoundFloat
class with __new__
and it flagged no errors.
Best Answer
What? Floats are immutable? But can't I do
Doesn't that "mut" x?
Well you agree strings are immutable right? But you can do the same thing.
The value of the variable changes, but it changes by changing what the variable refers to. A mutable type can change that way, and it can also change "in place".
Here is the difference.
Concrete examples