Is it possible to "lock" context attributes?

[lu-maca]

Hi,

Is there a way to raise a warning when trying to overwrite a certain attribute of context? For example:

# environment.py
-----------------

@fixture
def fixture_test(ctx):
    ctx.locked_attribute = SomeImportantClass()
    yield ctx.locked_attribute
    ctx.locked_attribute.clear()

# steps.py
-----------------
@step("This step shall do something")
def do_something(ctx):
    # do something
    ctx.locked_attribute = "foo" # I would like to raise here a warning
    ctx.locked_attribute.method_of_SomeImportantClass() # error is raised by python
    

Is this possible? For example, is there a way to raise a behave.runner.ContextMaskWarning as said in the documentation [1]?

[1] "If an attempt made by user code to overwrite one of these variables, or indeed by behave to overwite a user-set variable, then a behave.runner.ContextMaskWarning warning will be raised."

[jenisys]

behave does not protect user context variables. As you have stated, it raises only such a warning if you try to override/hide a behave context variable.

Currently, you will need to provide such a special ValueObject class, like a Constant object that protects itself against assignment (and raises a ContextMaskWarning if an assignment occurs).

NOTES:
Normally, you need a use_or_create_context_param(ctx, name, some_factory_func, *args, **kwargs) helper function that provides/stores a context variable is none exists.

EXAMPLE:

from behave import given, when, then, step
from behave4me.step_util import use_or_create_context_param

@step(„This step shall do something“)
def do_something(ctx):
    # — NOTE: ctx.locked_attribute is only created/assigned if no such named attribute exists.
    locked_attribute = use_or_create_context_param(ctx, „locked_attribute“, SomeImportantClass)
    locked_attribute.method_of_SomeImportantClass()

SEE ALSO:

• https://pypi.org/project/kkconst/
• … (other such projects on https://pypi.org )

[lu-maca]

When developing a library that uses behave as a framework, it should be probably a good solution to have some "locked" attribute in ctx, without forcing the user to use use_or_create_context_param(...) to be sure s/he does not overwrite some important library related ctx attributes (or at least to let her/him know that s/he's doing that).

Is this a valid point to you?

[jenisys]

Sorry, no.

I basically means that you do not have control of your own code that registers Context attributes. Therefore, you want to have a safety net.

HINT:
Use descriptors or something similar to achieve what you desire.

SEE ALSO:

• https://docs.python.org/3/howto/descriptor.html#descriptorhowto

[jenisys]

SEE ALSO:

• Context.use_or_create_param(name, ...)
• Context.use_or_assign_param(name, value)