def open_pdb(code):
    url = "https://files.rcsb.org/view/%s.pdb" % code
    import urllib.request, io
    return io.TextIOWrapper(urllib.request.urlopen(url))

def average_coord(code):
    f = open_pdb(code)
    sum_x = sum_y = sum_z = 0.0
    num_atoms = 0
    for line in f:
        if not line.startswith("ATOM"):
            continue
        sum_x += float(line[30:38])
        sum_y += float(line[38:46])
        sum_z += float(line[46:54])
        num_atoms += 1
    if num_atoms == 0:
        print("no atoms were found")
    else:
        avg_x = sum_x / num_atoms
        avg_y = sum_y / num_atoms
        avg_z = sum_z / num_atoms
        print("average coordinates of ", num_atoms, "atoms:", avg_x, avg_y, avg_z)
    f.close()

average_coord("3FX2")