fix .mesh file generated by tetgen to fit igllib

f_in = open("character2_5000.1.mesh")  
f_out = open("character2_5000.2.mesh", "w")  
lines = f_in.readlines()
start = False
num = -1
for line in lines:
        if not(start):
                f_out.write(line)
                if line.strip() == 'Triangles':
                        start = True
        else:
                if num == -1:
                        num = int(line.strip())
                        f_out.write(line)
                else:
                        if num != 0:
                                numbers = list(map(int, line.split()))  
                                f_out.write("%d %d %d %d\n" % (numbers[0], numbers[2], numbers[1], numbers[3]))
                                num -= 1
                        else:
                                start = False
                                
print("done!")  
f_out.close()  
f_in.close()