[web2py] field default lambdas being executed always?

[Carlos]

Hi,

Why are field default lambdas being executed always (as part of 
define_table)?.

* Example:

   def xdefault(v):
       print '===== VALUE > %s' % v
       return v

   db.define_table(
       'xtable',
       Field('xfield1', default=lambda: xdefault('v1')),
       Field('xfield2', default=lambda: xdefault('v2')),
       Field('xfield3', default=lambda: xdefault('v3')),
   )

* Output:

   ===== VALUE > v1
   ===== VALUE > v2
   ===== VALUE > v3

* Stack trace for one of them:

   File C:\web2py\gluon\dal.py in define_table at line 4156
      
self._adapter.create_table(t,migrate=migrate,fake_migrate=fake_migrate,polymodel=polymodel)
   File C:\web2py\gluon\dal.py in create_table at line 551
      not_null = self.NOT_NULL(field.default,field.type)
   File C:\web2py\gluon\dal.py in NOT_NULL at line 750
      return 'NOT NULL DEFAULT %s' % self.represent(default,field_type)
   File C:\web2py\gluon\dal.py in represent at line 1200
      obj = obj()
   File C:\web2py\applications\test\models\db.py in <lambda> at line 88
      ... Field('xfield', default=lambda: xdefault('===== VALUE =====')), 
...
   File C:\web2py\applications\test\models\db.py in xdefault at line 83

I thought it was safe to put lambdas as field default values with the 
certainty that they won't be executed unless / until absolutely required 
(when new instances of the table are created without such default values), 
i.e. deferred execution.

Is this the expected behavior?.

p.s. I'm using trunk.

Thanks,

   Carlos