Calculate the size of uploaded file using compute and lambda function compute

from os import path



db.define_table('file',

   Field('name', 'string', label=T('File Name')),

   Field('website_url','string', length="512", label=T('Source Link')),

   Field('table_name',readable=False, writable=False),

   Field('record_id','integer',readable=False, writable=False),

   Field('title', label=T('Title'), notnull=True),

   Field('comment', label=T('Comment')),

   Field('version','string', length="32", label=T('Version Number')), 

   Field('file', 'upload', autodelete=True, label=T('File')),

   Field('size', 'double', readable=False, writable=False, label=T('Size')),

   format='%(title)s'

   )

db.file.size.compute = lambda row: path.getsize(path.join(request.folder,'uploads',row.file))

def show_files():

    files= db(db.file>0).select()

    return dict(files=files)

 {{for record in files:}}

           <div class="visible_result">

                <a rel="nofollow" href="{{=URL('references','download', args=record.file)}}" target="_blank" class="list-group-item" target="_blank">                        

                <h4 class="list-group-item-heading">{{=record.name}}<small> Version: {{=record.version}}</small></h4>

                 <p class="list-group-item-text">

                  {{if record.size:}} 

                      {{if record.size<1000000:}}

                           {{=record.size/1000 }} kB 

                       {{else:}}

                           {{=record.size/1000/1000 }} mB 

                        {{pass}}- {{=record.comment}}

                    {{pass}}                                

                    </p>

                 </a>

             </div>

{{pass}}