Python Class 属性表现为字典

Question

I have a very simple class that defines properties like:

class Person:
    fields = set()

    @property
    def id(self):
        self.fields.add('id')
        return 'person.id'

The idea is for this class to record which properties have been accessed. Now the problem comes when I need to start supporting: person.metadata.key where metadata is basically an HStore object or 1 level JSON, the key is arbitrary and the idea is for the class Person so record access to any of the keys in metadata . I tried something like this:

class CustomerBulkContext:

    fields = set()

    class PersonMetadata:
        def __getitem__(self, attr):
            fields.add(f'metadata.{attr}')
            return f'person.metadata.{attr}'

    metadata = CustomerMetadataContext()

Now obviously the problem is that fields inside PersonMetadata is not a known variable at this point. How can I overcome this issue, I don't know if it's possible to do in Python without too much code.

Answer 1

In order to track accesses like person.metadata.key you'd have to have person.metadata return an object which itself tracks how it was accessed. In order to track the whole chain, you'd pass the chain so far to the object.

Something like:

class AccessTracker:
    def __init__(self, path=()):
        self._path = path

    def __getattr__(self, name):
        print('Accessed %s in %s' % (name, self._path))
        return AccessTracker(self._path + (name,))