Temur, thanks for your response.
I try all of that, but always same problem ("AttributeError: object has no attribute 'strftime'."). An other idea ?
<filter string="This 1" domain="[(strptime('date','%%m'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 2" domain="[(time.strptime('date','%%m'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 3" domain="[(date.strptime('date','%%m'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 5" domain="[(datetime.date.strptime('date','%%Y-%%m-%%d'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 6" domain="[(datetime.time.strptime('date','%%Y-%%m-%%d'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 7" domain="[(datetime.datetime.strptime('date','%%m'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 4" domain="[(datetime.strptime('date','%%Y-%%m-%%d'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 5" domain="[(datetime.date().strptime('date','%%m'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 6" domain="[(datetime.time().strptime('date','%%m'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 7" domain="[(datetime.datetime().strptime('date','%%m'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 5" domain="[(datetime.date().strptime('date','%%Y-%%m-%%d'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 6" domain="[(datetime.time().strptime('date','%%Y-%%m-%%d'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 7" domain="[(datetime.datetime().strptime('date','%%Y-%%m-%%d'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 10" domain="[(datetime.date('date'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 11" domain="[(datetime.time('date'),'=', ((context_today()).strftime('%%m')))]"/>
<filter string="This 12" domain="[(datetime.datetime('date'),'=', ((context_today()).strftime('%%m')))]"/>
filter string="This 11" domain="[(datetime.time('date').strftime('%%m'),'=', ((context_today()).strftime('%%m')))]"/>
EDIT :
Finally, i found the solution : sale.report is not a real model, it's a view. For add field, you need to overwrite select method. So :
class sale_report(osv.osv):
_inherit = 'sale.report'
date_order_month = fields.Char(string='Date Month')
date_order_day = fields.Char(string='Date Day')
def _select(self):
select_str = """
SELECT min(l.id) as id,
l.product_id as product_id,
t.uom_id as product_uom,
sum(l.product_uom_qty / u.factor * u2.factor) as product_uom_qty,
sum(l.product_uom_qty * l.price_unit * (100.0-l.discount) / 100.0) as price_total,
count(*) as nbr,
s.date_order as date,
date_part('month', s.date_order) as date_order_month,
date_part('day', s.date_order) as date_order_day,
s.date_confirm as date_confirm,
s.partner_id as partner_id,
s.user_id as user_id,
s.company_id as company_id,
extract(epoch from avg(date_trunc('day',s.date_confirm)-date_trunc('day',s.create_date)))/(24*60*60)::decimal(16,2) as delay,
s.state,
t.categ_id as categ_id,
s.pricelist_id as pricelist_id,
s.project_id as analytic_account_id,
s.section_id as section_id
"""
return select_str