file.stem访问不带扩展名的文件的基本名称。
file.with_stem()（在Python 3.9中添加的）返回一个带有新词干的更新的Path：

from pathlib import Path
file = Path('/Users/my_name/PYTHON/Playing_Around/testing_lm.py')
print(file.with_stem(f'A_{file.stem}'))

\Users\my_name\PYTHON\Playing_Around\A_testing_lm.py

使用file.parent获取路径的父级，使用file.name获取最终路径组件，不包括驱动器和根目录。

from pathlib import Path
file = Path('/Users/my_name/PYTHON/Playing_Around/testing_lm.py')

file_prexif_lst = ['A','B','C']

for prefix  in file_prexif_lst:
    p = file.parent.joinpath(f'{prefix}_{file.name}')
    print(p)

/Users/my_name/PYTHON/Playing_Around/A_testing_lm.py
/Users/my_name/PYTHON/Playing_Around/B_testing_lm.py
/Users/my_name/PYTHON/Playing_Around/C_testing_lm.py

类似于@Mark Tolonen的答案，但使用的是file.with_name方法（对我来说，这比“stem”更容易记住）

from pathlib import Path

file = Path('/home/python/myFile.py')
prefix = 'hello'

new_file = file.with_name(f"{prefix}_{file.name}")
print(new_file)

OUTPUT:
/home/python/hello_myFile.py