You are asking about two things

1- How to print a report(and get the binary data perhaps?)

result = self.pool.get('report').get_pdf(cr, uid, [res_id], report_name, context=ctx)

where:

• res_id is the id of the object to use in the report related to the model of the report, 

• report_name is the name of the report to print used to locate the report template

• result is the binary data of the pdf report
  

2- How get an already saved Odoo report file

obj = self.pool.get(report.model).browse(cr, uid, rec_id)
filename = eval(report.attachment, {'object': obj, 'time': time})
alreadyindb = [('datas_fname', '=', filename),('res_model', '=', report.model),('res_id', '=', rec_id)]
attach_ids = self.pool.get('ir.attachment').search(cr, uid, alreadyindb)
if attach_ids:
    pdf = self.pool.get('ir.attachment').browse(cr, uid, attach_ids[0]).datas
    pdf = base64.decodestring(pdf)