I am returning `5` for my computational field `old_default_code`, and I am getting the following error:

> 
> ValueError: dictionary update sequence element #0 has length 1; 2 is required
> 
> 
> 

What am I doing wrong?

**Python code of the function:**

```
def _old_default_code(self, cr, uid, ids, name, arg, context=None):
        return '5'
_columns = {
            'old_default_code' : fields.function(_old_default_code, type='char', size=32, method=True, store=False, multi=False) }

```

**XML code:**

```
<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <!-- mrp_bom -->
        <record id="adamson_mrp_bom_form_view" model="ir.ui.view">
            <field name="name">adamson.mrp.bom.form.view</field>
            <field name="model">mrp.bom</field>
            <field name="type">form</field>
            <field name="inherit_id" ref="mrp.mrp_bom_form_view" />
            <field name="arch" type="xml">

                <xpath expr="//notebook/page[@string='Components']/field/tree[@string='Components']/field[@name='sequence']" position="before" >
                                         <field name="old_default_code" />
                     <button class="oe_inline oe_stat_button" type="object" string="Go!" icon="gtk-go-forward" name="action_go" 
                     attrs="{'invisible':[('old_default_code','=', '5')]}"  />

                               </xpath>

```