Python Immutable
In Python there is no simple way to create an immutable class directly. You could create a class that uses __slots__ and then use__setattr__ to prevent changes to the variables but there is a trivially simple way to create an immutable class which effectively can act as a struct in Python this is by using a namedtuple. This is nice because a tuple is by its nature an immutable. Let us take a simple 2d point which has an X and a Y
You could do this code:
Point = collections.namedtuple('Point', 'x y')
p=Point(1,1)
print("x={} y={}".format( p.x, p.y))
p.x=7
Now this code will work to a point. The code will print this
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
7 print("x={} y={}".format( p.x, p.y))
8
----> 9 p.x=7
AttributeError: can't set attribute
Note how we have our Point(…) object but we can not change it we must create a new Object hence why the p.x=7 causes the stack trace,. Yes you may have noticed I do use Jupyter to test my code for these blogs.
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You could do this code:
import collections
Point = collections.namedtuple('Point', 'x y')
p=Point(1,1)
print("x={} y={}".format( p.x, p.y))
p.x=7
Now this code will work to a point. The code will print this
x=1 y=1
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
7 print("x={} y={}".format( p.x, p.y))
8
----> 9 p.x=7
AttributeError: can't set attribute
Note how we have our Point(…) object but we can not change it we must create a new Object hence why the p.x=7 causes the stack trace,. Yes you may have noticed I do use Jupyter to test my code for these blogs.
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