watched nested dependencies throws AttributeError

[tjader]

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ALL software version info

(this library, plus any other relevant software, e.g. bokeh, python, notebook, OS, browser, etc)
param v 1.12.3
Reproducible at least on on python 3.10 on Ubuntu.

Description of expected behavior and the observed behavior

The error below is thrown when I try nested parameterized dependencies, where there is a watch on a nested dependency. I would expect that the watch flag should work in these circumstances.

Complete, minimal, self-contained example code that reproduces the issue

import param

class A(param.Parameterized):
    x=param.Number(default=0)

class B(param.Parameterized):
    a=param.ClassSelector(A, default=A())

    @param.depends('a.x', watch=True)
    def y(self):
        pass


class C(param.Parameterized):
    b=param.ClassSelector(B, default=B())



c = C()

Stack traceback and/or browser JavaScript console output

  File "/home/mats/miniconda3/envs/quant/lib/python3.10/site-packages/IPython/core/interactiveshell.py", line 3398, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-2-c31ab72dd48f>", line 1, in <cell line: 1>
    runfile('/home/mats/.config/JetBrains/PyCharm2022.2/scratches/scratch_2.py', wdir='/home/mats/.config/JetBrains/PyCharm2022.2/scratches')
  File "/home/mats/.local/share/JetBrains/Toolbox/apps/PyCharm-P/ch-0/222.4345.23/plugins/python/helpers/pydev/_pydev_bundle/pydev_umd.py", line 198, in runfile
    pydev_imports.execfile(filename, global_vars, local_vars)  # execute the script
  File "/home/mats/.local/share/JetBrains/Toolbox/apps/PyCharm-P/ch-0/222.4345.23/plugins/python/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "/home/mats/.config/JetBrains/PyCharm2022.2/scratches/scratch_2.py", line 20, in <module>
    c = C()
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/site-packages/param/parameterized.py", line 3173, in __init__
    self.param._setup_params(**params)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/site-packages/param/parameterized.py", line 1387, in override_initialization
    fn(parameterized_instance, *args, **kw)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/site-packages/param/parameterized.py", line 1633, in _setup_params
    self.param._instantiate_param(p)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/site-packages/param/parameterized.py", line 1688, in _instantiate_param
    new_object = copy.deepcopy(param_obj.default)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 271, in _reconstruct
    state = deepcopy(state, memo)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 297, in _reconstruct
    value = deepcopy(value, memo)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 206, in _deepcopy_list
    append(deepcopy(a, memo))
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 265, in _reconstruct
    y = func(*args)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 264, in <genexpr>
    args = (deepcopy(arg, memo) for arg in args)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/copy.py", line 273, in _reconstruct
    y.__setstate__(state)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/site-packages/param/parameterized.py", line 3227, in __setstate__
    watcher_args[2] = _m_caller(self, fn._watcher_name)
  File "/home/mats/miniconda3/envs/quant/lib/python3.10/site-packages/param/parameterized.py", line 661, in _m_caller
    function = getattr(self, method_name)
AttributeError: 'A' object has no attribute 'y'

When a default value is given to a ClassSelector (like in C above), a deepcopy of that default value happens, and it is the deepcopy that is causing the exception, so a shorter example wold be to just do:

import param
import copy

class A(param.Parameterized):
    x=param.Number(default=0)

class B(param.Parameterized):
    a=param.ClassSelector(A, default=A())

    @param.depends('a.x', watch=True)
    def y(self):
        pass

copy.deepcopy(B())

Removing the "watch" flag removes the issue, but I also lose the watched updates that I need.

[maximlt]

Traceback from the shorter example above:

Traceback (most recent call last):
  File ".mltmess/issue_deepcopy.py", line 14, in <module>
    copy.deepcopy(B())
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 270, in _reconstruct
    state = deepcopy(state, memo)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 296, in _reconstruct
    value = deepcopy(value, memo)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 205, in _deepcopy_list
    append(deepcopy(a, memo))
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 264, in _reconstruct
    y = func(*args)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 263, in <genexpr>
    args = (deepcopy(arg, memo) for arg in args)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/Users/mliquet/miniconda3/envs/panel38/lib/python3.8/copy.py", line 272, in _reconstruct
    y.__setstate__(state)
  File "/Users/mliquet/dev/param/param/parameterized.py", line 3305, in __setstate__
    watcher_args[2] = _m_caller(self, fn._watcher_name)
  File "/Users/mliquet/dev/param/param/parameterized.py", line 670, in _m_caller
    function = getattr(self, method_name)
AttributeError: 'A' object has no attribute 'y'