On Friday 09 June 2006 13:35, Rudolph wrote: > Hi, > > I understand why we have the django.db.models.LazyDate(): it's to > make sure we get the datetime value at execution time and not at > "compile" time. The docs tell you to use it for "limit_choices_to", > but should I also use it when I want the default value of a > DateTimeField to be "now". And how about inside model methods, > manager methods and view functions? I guess one should/can use > datetime.now() in those places, but I'm not sure. Can anyone provide > some info on this subject? It might also be interesting to add this > to the docs.
For DateTimeFields, please have a look at the docs: http://www.djangoproject.com/documentation/model_api/ Also, the 'default' value can be a callable (I think), so you can use 'default=datetime.now'. (NB: not 'default=datetime.now()') When thinking about lazy objects, the rules are the same as normal Python. You have to think about when the code will be evaluated. Note this is different from 'compiled' -- Python code is compiled first of all to bytecode, and usually stored in a .pyc file. Before it can be used, the bytecode must be evaluated. This occurs when the module is first imported in a Python process, and it creates at runtime all the classes and functions that exist in that module. Example: ### mymodule.py from datetime import datetime module_created = datetime.now() class MyClass: class_created = datetime.now() def __init__(self): self.instance_created = datetime.now() def mydate(): return datetime.now() # Advanced example def create_a_class(): class SomeClass: class_created = datetime.now() return SomeClass ### end Fromsome other code, or a prompt, you will get this: >>> mymodule.module_created <The datetime the module was imported> >>> mymodule.MyClass.class_created <The datetime the module was imported> >>> m = MyClass() >>> m.instance_created <2 seconds ago i.e. when you called MyClass.__init__()> >>> mydate() <Now> >>> create_a_class().class_created <Now> LazyDate exists for the first two cases, which includes the definition of models like in Django. It isn't needed for the rest. Don't worry if you didn't understand the last one, but it's actually consistent. (There is one more case to worry about - default arguments to functions and methods are evaluated when the function is defined, not when it is called.) Luke -- The probability of someone watching you is proportional to the stupidity of your action. Luke Plant || L.Plant.98 (at) cantab.net || http://lukeplant.me.uk/ --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users -~----------~----~----~----~------~----~------~--~---
