Support @cached decorator on properties of the environment class

[Ryan J Ollos]

The proposed change should allow @cached to be used on properties of the Environment class.

[Ryan J Ollos]

I tried:

from trac.env import Environment
env = instance if isinstance(instance, Environment) else instance.env

The local import is required to avoid a circular import since trac.env imports CacheManager.

Or we could test whether the object is a ComponentManager instance: log:rjollos.git:t11867.

[Peter Suter]

Testing for ComponentManager sounds good.

(Another possibility might be to add an env property returning self to Environment, or would that be too confusing?)

[Ryan J Ollos]

Replying to psuter:

(Another possibility might be to add an env property returning self to Environment, or would that be too confusing?)

While working on #7339 and encountering this issue, as a workaround I initially added self.env = self at tags/trac-1.0.2/trac/env.py@:276#L265​. Is that what you had in mind?

[Jun Omae]

Sounds a good idea. But I think that adding self.env = self would be a circular reference. Instead, it would be good to add env method with property decorator like this.

    @property
    def env(self):
        return self

[Ryan J Ollos]

Do you have a particular use-case in mind where self.env = self causes a problem that is not seen with the property definition? There are similar references in tags/trac-1.0.2/trac/config.py@:573#L555​. That's a class attribute that contains a dictionary, but otherwise looks like a similar pattern.

At least for this simple case, the property x and instance attribute y appear to behave the same:

>>> class A(object):
...   @property
...   def x(self):
...     return self
...   def __init__(self):
...     self.y = self
...     self.z = 1
... 
>>> a = A()
>>> a
<__main__.A object at 0x7f5b22038450>
>>> a.y
<__main__.A object at 0x7f5b22038450>
>>> a.y.y
<__main__.A object at 0x7f5b22038450>
>>> a.y.y.z
1
>>> a.x
<__main__.A object at 0x7f5b22038450>
>>> a.x.x
<__main__.A object at 0x7f5b22038450>
>>> a.x.x.z
1

[Ryan J Ollos]

Committed to 1.0-stable in [13476], merged to trunk in [13477].