Unexpected behaviour of param.edit_constant() context manager

[dinya]

From param.edit_constant() docstring:

Temporarily set parameters on Parameterized object to constant=False to allow editing them.

Should "temporarily" mean "set editable inside context manager and unset outside"?

If so the following behaviour is unexpected.

import param

class A(param.Parameterized):
    val = param.Integer(1, constant=True)

a = A()

#print(a.param.val.constant, a.param.val.readonly)

with param.edit_constant(a):
    a.val = 6

print(a.param.val.constant, a.param.val.readonly)

# "TypeError: Constant parameter 'val' cannot be modified" is expected to be raised:
a.val = 7

... but nothing is raised and it prints:

False False

But if I change my code slightly (uncomment first print)

import param

class A(param.Parameterized):
    val = param.Integer(1, constant=True)

a = A()

print(a.param.val.constant, a.param.val.readonly)
# or just call a.param.val

with param.edit_constant(a):
    a.val = 6

print(a.param.val.constant, a.param.val.readonly)

# "TypeError: Constant parameter 'val' cannot be modified" is expected to be raised:
a.val = 7

then it prints

True False
True False

and TypeError: Constant parameter 'val' cannot be modified is raised as expected.

It seems that the param.edit_constant() context manager doesn't restore the state if a.param.val has not been called before.

---

My environment:

1. python 3.11.9
2. param 2.2.0

[maximlt]

Hi @dinya, it seems like when you copied your code over to this issue the indentation got wrong, for instance this is not valid Python:

with param.edit_constant(a):
a.val = 6

Could you please edit your post to fix the indentation?

[dinya]

@maximlt Thanks, I fixed it.

[maximal]

@dinya, you‘re welcome!

[maximlt]

This is indeed a bug and a potential duplicate of #931, thanks for reporting it @dinya !