Delete duplicate rows in textfile - except it contains a "{" or "}"

[Joon Ki Choi]

lines_seen = set() # holds lines already seen
outfile = open("literatur_clean.txt", "w")
for line in open("literatur_dupl.txt", "r"):
    if ('{' in line or '}' in line) or line not in lines_seen:
        outfile.write(line)
        lines_seen.add(line)
outfile.close()