default_error_messages is an dictionary with 5 initial entries: return value of the function _ called with an argument string,
default_error_messages = { 'invalid' : _ ( "No file was submitted. Check the encoding type on the form." ) , 'missing' : _ ( "No file was submitted." ) , 'empty' : _ ( "The submitted file is empty." ) , 'max_length' : ungettext_lazy ( 'Ensure this filename has at most %(max)d character (it has %(length)d).' , 'Ensure this filename has at most %(max)d characters (it has %(length)d).' , 'max' ) , 'contradiction' : _ ( 'Please either submit a file or check the clear checkbox, not both.' ) }