python中字典相关问题

Question

sentence="Life is short,we need python." sentence=sentence.lower() counts={} for c in sentence: if c in counts: counts[c]=counts[c]+1 else: counts[c]=1 print(counts) 提问：counts不是一个空字典吗？也没有将sentence中的内容写入counts怎么内容自己就进去了？

Answer 1

counts[c]=1 这样已经对字典的键值赋值了啊

for c in sentence: 是循环 sentence字符串中每一字符，

循环中c的值每次循环依次是 “l”,“i”,“f”......

比如第一次循环 c的值是 “l”，执行counts[c]=1就是对counts字典中添加一个"l"的键,值初始设置为1 

counts字典就变成 {"l":1}