dict的len的意外行为

Question

我期望len（邮件）返回100，但我得到101。有人能解释我为什么会有这种行为吗

items_by_post = {}

for i in joined:
    if i['post_code'] in items_by_post:
        items_by_post[i['post_code']].append(i)
    elif len(items_by_post)<=100 and i['post_code'] not in items_by_post:
        items_by_post[i['post_code']]=items_by_post.get(i['post_code'],[])
        items_by_post[i['post_code']].append(i)
    else:
        continue

Answer 1

您的代码调用append()，而len(items_by_post) <= 100。因此，当len(items_by_post) == 100时，您的代码将append()另一项，将len(items_by_post)增加到101