TypeError: 'NoneType' object is not iterable 一次错误场景

TypeError: 'NoneType' object is not iterable

源码

def get_url(lines):
    
    urls=[]
    for line in lines:
        if 'img' in urls:
            url=line.split('src=')[-1].split('"')[1]
            urls.append(url) 
    
def outputto(urls):
    count=0
    for line in urls:
        print('第{:2}个url为{}'.format(count,line))
        count=count+1

意思是urls里面的内容为空
向上找发现 上面的get_url 函数未添加return 返回值
需要在下面的函数调用，所以返回报错
运行后在for line in urls 报错