I am trying to add a boolean field to hr_holiday that should enable me to not count weekends on leaves when checked.

I get the following error:

ParseError: "Invalid view definition

Error details:

Field `weekend_exclude` does not exist

Error context:

View `excluding.days.leaves`

[view_id: 700, xml_id: n/a, model: hr.holidays, parent_id: n/a] ...

weekend_leaves_view.xml

<?xml version="1.0" encoding="UTF-8"?> 
<openerp>   
 <data>       
 <record model="ir.ui.view" id="excluding_days_leaves"> 
 <field name="name">excluding.days.leaves</field>      
 <field name="model">hr.holidays</field>       
 <field name="arch" type="xml">        
 <form string="Session Form">        
 <sheet>             
 <group>               
 <group string="Weekend Leave">  
 <field name='weekend_exclude'/>  
 </group> 
 </group>     
 </sheet>      
 </form>      
 </field>    
 </record>     
 <record model="ir.actions.act_window" id="excluding_days_leaves_action"> 
 <field name="name">Excluding days</field>  
 <field name="res_model">hr.holidays</field>  
 <field name="view_type">form</field>         
 <field name="view_mode">form</field>     
 </record>    
 <record model="ir.actions.act_window.view" id="excluding_days_leaves_action_form">   
 <field name="view_mode">form</field>     
 <field name="view_id" ref="excluding_days_leaves"/>         
 <field name="act_window_id" ref="excluding_days_leaves_action"/>   
 </record>  
 <menuitem id="excluding_days_leaves_menuitem" name="Excluding days" parent="hr_holidays.menu_hr_holidays_root" action="excluding_days_leaves_action"/> 
 </data>
 </openerp>

model.py

from openerp.osv import fields, orm
import datetime
class nites_weekend_leaves(orm.Model):
 _inherit = 'hr.holidays'
 weekend_exclude=fields.boolean('Weekend')
 def _get_number_of_days(self, date_from, date_to):        """Returns a float equals to the timedelta between two dates given as string."""
 DATETIME_FORMAT = "%Y-%m-%d %H:%M:%S"        from_dt = datetime.datetime.strptime(date_from, DATETIME_FORMAT)
 to_dt = datetime.datetime.strptime(date_to, DATETIME_FORMAT)        
 timedelta = to_dt - from_dt
 weekend_days=0
 if self.weekend_exclude:            
    while from_dt < to_dt:
      if from_dt.weekday()==5 or from_dt.weekday()==6: #count how many saturdays and sundays
      weekend_days += 1
      from_dt=from_dt+datetime.timedelta(days=1)
 diff_day = timedelta.days - weekend_days + float(timedelta.seconds) / 86400 
 return diff_day