python - Why won't Django Model's time field default properly to utcnow() as expected? -


here model:

class mymodel(models.model):     timestamp = models.datetimefield(default=datetime.datetime.utcnow())     def __unicode__(self):         return "mymodel id=%s @ <%s %s>" % (             self.id,              self.timestamp.strftime("%h:%m:%s.000").rstrip("0").rstrip("."),              self.timestamp.strftime("%m/%d/%y")         )

look happens when run commands console:

>>> myapp.models import * >>> import datetime  >>> mymodel() <mymodel: mymodel id=none @ <02:04:45 03/25/2014>>  >>> # wait several seconds >>> mymodel() <mymodel: mymodel id=none @ <02:04:45 03/25/2014>>  >>> # wait several seconds >>> mymodel() <mymodel: mymodel id=none @ <02:04:45 03/25/2014>>   >>> # wait several seconds >>> mymodel(timestamp=datetime.datetime.utcnow()) <mymodel: mymodel id=none @ <02:07:16 03/25/2014>>  >>> # wait several seconds >>> mymodel() <mymodel: mymodel id=none @ <02:04:45 03/25/2014>>  >>> # wait several seconds >>> mymodel() <mymodel: mymodel id=none @ <02:04:45 03/25/2014>>

why default value of timestamp (which supposed assigned datetime.datetime.utcnow() each mymodel) stay same first 1 created?

the time changes if manually set value in constructor ugly hack!

it looks default value getting cached , continually re-used. how prevent caching happening?

because you've called it. pass function instead.

timestamp = models.datetimefield(default=datetime.datetime.utcnow)

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