Thank you Jonathan,
This is indeed helpful, I have completely forgotten about these.
However, in my case, defaults are not callable defaults, but rather default
values preset at a higher level object and it has little to do with function
defaults.
Although, I think it is possible to reshape the problem to use the mechanism
you have provided. For example:
class Node:
def __init__(self, a=1):
self.a = a
class Container:
def __init__(self, a):
self.node_defaults = dict()
self.node_cls = Node
self.node_cls.__init__.__defaults__ = (a,)
# The issue, however is that it modifies the constructor from outside
# And it changes the Node class for the whole Runtime
# copy, deepcopy do not work here either
# Construct the node class programatically by inheritance leads to the
same issue:
# self.node_cls = type('Node2', (Node,), {})
# self.node_cls.__init__.__defaults__ = (a,)
self.nodes = list()
def new_node(self, *args, **kwds):
node = self.node_cls(*args, **kwds)
self.nodes.append(node)
return node
c = Container(a=2)
print(c.new_node().a) # 2
print(c.new_node(3).a) # 3
print(Node().a) # 2
If you could provide an example, which solves the same issue that I have
presented in a more elegant manner than simple dictionary storage, I would
appreciate it.
Kind regards,
DG
> On 18 Sep 2023, at 17:24, Jonathan Fine wrote:
>
> Hi Dom
>
> In your original post you used your proposed addition to write code that
> provides a way of handling defaults different from the standard mechanism,
> and perhaps in your opinion better.
>
> The following example tells us something about defaults mechanism already
> provided by Python:
>
> >>> def f(a, b=1, c=2): return a, b, c
> ...
> >>> f(0)
> (0, 1, 2)
> >>> f.__defaults__
> (1, 2)
> >>> f.__defaults__ = (0, 1, 2)
> >>> f()
> (0, 1, 2)
> >>> f.__defaults__ = (2, 1, 0)
> >>> f()
> (2, 1, 0)
>
> I am suspicious of your example in your original post because it does not
> explicitly consider the possibilities already provided by Python for changing
> default values on the fly.
>
> I hope this helps.
>
> Jonathan
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