lazy
Lazy attributes for Python objects
Package Contents
- @lazy
- A decorator to create lazy attributes.
Overview
Lazy attributes are computed attributes that are evaluated only once, the first time they are used. Subsequent uses return the results of the first call. They come handy when code should run
- late, i.e. just before it is needed, and
- once, i.e. not twice, in the lifetime of an object.
You can think of it as deferred initialization. The possibilities are endless.
Typing
The decorator is fully typed. Type checkers can infer the type of a lazy attribute from the return value of the decorated method.
Examples
The class below creates its store
resource lazily:
from lazy import lazy
class FileUploadTmpStore(object):
@lazy
def store(self):
location = settings.get('fs.filestore')
return FileSystemStore(location)
def put(self, uid, fp):
self.store.put(uid, fp)
fp.seek(0)
def get(self, uid, default=None):
return self.store.get(uid, default)
def close(self):
if 'store' in self.__dict__:
self.store.close()
Another application area is caching:
class PersonView(View):
@lazy
def person_id(self):
return self.request.get('person_id', -1)
@lazy
def person_data(self):
return self.session.query(Person).get(self.person_id)
Documentation
For further details please refer to the API Documentation.