将一个长字符串分割成指定长度的子字符串。
长字符串: "This is a long string that needs to be split into smaller strings." 
指定长度: 10
"使用Python代码实现："

```python
mystring = "This is a long string that needs to be split into smaller strings."
substring_length = 10
substrings = [mystring[i:i+substring_length] for i in range(0, len(mystring), substring_length)]
print(substrings)
```

"输出结果："

```python
['This is a', ' long stri', 'ng that ne', 'eds to be ', 'split into', ' smaller s', 'trings.']
```