Try it another ways

Here is step for filling default  value in ODOO8/9.

1. Go to Setting->Technical->Actions->User defined Defaults.

2. Create a record  for your model.

3. Inside name place your filed name(my_field).

4. Inside model place your model name(my.model).

5. inside Default value  place the default value (my_value) 

6. 
   

In python you can do it this way:

link_text = fields.Char(string='Link Text',default='Size Guide',required=True)

You have to do this in .py file

Some examples from  sale.py

Odoo 9:

• date_order = fields.Datetime(string='Order Date', required=True, readonly=True, index=True, states={'draft': [('readonly',     False)], 'sent': [('readonly', False)]}, copy=False, default=fields.Datetime.now)

• price_unit = fields.Float('Unit Price', required=True, digits=dp.get_precision('Product Price'), default=0.0)

Odoo 8:

'date_order': fields.datetime('Date', required=True, readonly=True, select=True, states={'draft': [('readonly', False)], 'sent':     [('readonly', False)]}, copy=False),

'price_unit': fields.float('Unit Price', required=True, digits_compute= dp.get_precision('Product Price'), readonly=True,     states={'draft': [('readonly', False)]}),

_defaults = {

        'date_order': fields.datetime.now,

        'price_unit': 0.0,

}

i want to do this in code when i write my form structure

<form>

<group>

     <field name="field_name" value="defaul_value"/> // when i clique on create button my field will have the value defaul_value not empty text did understand me

</group>