In New API, add Import api

from openerp import models, fields, api

class pb_it(models.Model):

	_inherit = 'res.partner'
        my_field = fields.Char(string='My Field', size=64) 

Sebastian782 If u have added a new field or modified a function inside the py file. You must restart the Odoo server. And then only u need to upgrade the server Otherwise this type of error may occur.  

this not resolve

I  had the same problem and i resolved it like this :

you have to add in your file.py :

from openerp import models,fields,api

and  precise in your init file this :

from . import file

The error appear when i am installing the module.

Import api did not changed anything.

Restarting the server does not change anything as i get an error 500 because the module installation failled.

Here below the full error:

 ParseError: "ValidateError
Field(s) `arch` failed against a constraint: Invalid view definition

Error details:
Field `my_field` does not exist

Error context:
View `view.res.partner.inherited`
[view_id: 1072, xml_id: n/a, model: res.partner, parent_id: 126]" while parsing file:///C:/Program Files (x86)/Odoo 8.0-20150826/server/openerp/addons/toto/views/menu.xml:4, near
<record model="ir.ui.view" id="view_res_partner_inherited">
			<field name="name">view.res.partner.inherited</field>
			<field name="model">res.partner</field>
			<field name="inherit_id" ref="base.view_partner_form"/>
			<field name="arch" type="xml">
				<field name="phone" position="after">
					<field name="my_field"/>
				</field>
			</field>
		</record>

class inherit_respartner(models.Model):
    _inherit = 'res.partner'
    myfield = fields.Char()

		<record model="ir.ui.view" id="add_respartner">
			<field name="name">add_respartner</field>
			<field name="model">res.partner</field>
			<field name="inherit_id" ref="base.view_partner_form" />
			<field name="arch" type="xml">
				<field name="email" position="after">
					<field name="myfield" />
				</field>
			</field>
		</record> 
I think it's the same, but it works in my module