自己写个range函数

def f(*args):
    if len(args)==1:
        start,end,step=0,args[0],1
    elif len(args)==2:
        start,end,step=args[0],args[1],1
    elif len(args)==3:
        start,end,step=args[0],args[1],args[2]
    else:
        raise Exception
    if step>0:
        while start<end:
            yield start
            start+=step
        raise StopIteration
    elif step<0:
        while start>end:
            yield start
            start+=step
        raise StopIteration
    else:
        raise("step can't be zero")