为什么我的程序不能使用整数7和9，而是所有其他程序？

I have pinpointed the error to the make_barcode function, and the gc_cont function, but can't figure it out. Also, I'm not sure if i'm using the class instances correct... I can't seem to generate a random barcode that has between 45% and 55% gc content.I have pinpointed the error to the make_barcode