In your XML View definition put:

<button name=print_report" string="Print" type="object">

In your class definition add a new method:

    def print_report(self, cr, uid, ids, context=None): 
        return {
            'type': 'ir.actions.report.xml',
            'report_name': 'my.report.name',
             'nodestroy' : True
        }

Your report action XML should be like:

		<record id="my_report" model="ir.actions.report.xml">
			<field name="name">my report name</field>
			<field name="report_name">my.report.name</field>
			<field name="model">report.model</field>
			<field name="auto" eval="False"/>
                        <field name="is_pentaho_report" eval="True"/>
			<field name="pentaho_report_model_id" ref="module.model_report_model"/>
			<field name="pentaho_report_output_type">pdf</field>
			<field name="pentaho_filename">module/report/my_report.prpt</field>
			<field name="pentaho_load_file" eval="True"/>
		</record

Button @name and print method should have the same name

Also report_name should be the same in method and report action XML

Be very careful setting pentaho_report_model_id. Format is: module name with no spaces + ".model_" + report model with dots converted to underscores