Odoo 10 - Custom Button with Action (Posting JSON customer data help !!)

Hi i have been able to create a button in the account.invoice with the following code in xml

<record id="invoice_form_shippinglabel" model="ir.ui.view">

            <field name="name">account.invoice.form.shippinglabel</field>

            <field name="model">account.invoice</field>

            <field name="inherit_id" ref="account.invoice_form"/>

            <field name="arch" type="xml">

       <header>

           <button name="label" string="Print Shipping Label" class="oe_highlight"/>

                </header>

   </field>

</record>

Now i want to add function after user press the button

so in my 'models.py' i have try to put this code

def label(self):

        data = {

    'ids': [12, 3, 4, 5, 6]

  }

  req = urllib2.Request('https://requestb.in/1bz11jv1')

  req.add_header('Content-Type', 'application/json')

  response = urllib2.urlopen(req, json.dumps(data))

so basically, i want to send some sample data to https://requestb.in/1bz11jv1

but it doesn't work when i restart odoo it give me this error in odoo.log

  File "/odoo/odoo-server/addons/labelprint/models/models.py", line 14
    def label(self):
    ^
IndentationError: unexpected indent

Am not very sure why it cause that error i have googled about Indentation and it doesnt help at all

Also i have a little more question on  if i can post json data already

how do i get information like customer.address , customer.phone, customer.name because i will be need these in sending json data

Thank you very much