list(str[3,4])=[3,4]
时间: 2024-01-09 07:06:05 浏览: 16
这段代码有问题,应该改成以下形式才能实现将列表中第3到第4个元素修改为3和4:
```python
lst = [1, 2, 3, 4, 5]
lst[2:4] = [3, 4]
print(lst)
```
输出结果为:`[1, 2, 3, 4, 5]`。注意,这里的索引是从0开始的,所以第3到第4个元素的索引分别是2和3。
相关问题
Dict[str, List[str]] = defaultdict(list)
This line of code creates a default dictionary where the keys are strings and the values are lists of strings. The default value for any new key is an empty list.
For example, if we have the following code:
```
from collections import defaultdict
my_dict: Dict[str, List[str]] = defaultdict(list)
my_dict["key1"].append("value1")
my_dict["key2"].append("value2")
my_dict["key1"].append("value3")
print(my_dict)
```
The output will be:
```
defaultdict(<class 'list'>, {'key1': ['value1', 'value3'], 'key2': ['value2']})
```
Here, we can see that the dictionary has two keys, "key1" and "key2". The values for "key1" are the list ["value1", "value3"], and the value for "key2" is the list ["value2"]. Since we used a default dictionary, we did not need to check if the keys had been initialized with an empty list before appending values to them.
list(str[3,4])==[3,4]的值为什么是false
这是因为你使用了错误的语法。`str[3,4]`表示获取字符串 `str` 中下标为 3 和 4 的字符,但是这样的语法是错误的,应该使用 `str[3:5]` 表示获取字符串 `str` 中下标从 3 到 4 的字符子串。而 `list(str[3:5])` 表示将字符子串转换为列表,其值为 `['3', '4']`,因此 `list(str[3:5])==[3,4]` 的值是 `False`。