def record_strip_controlfields(rec):
for tag in list(rec.keys()):<EOL><INDENT>if tag[:<NUM_LIT:2>] == '<STR_LIT>' and rec[tag][<NUM_LIT:0>][<NUM_LIT:3>]:<EOL><INDENT>del rec[tag]<EOL><DEDENT><DEDENT>
Remove all non-empty controlfields from the record.

:param rec:  A record dictionary structure
:type  rec:  dictionary