import os

def group_and_join_filenames(filenames, delimiter='.'):
    result = {}
    for filename in filenames:
        prefix = os.path.splitext(filename)[0]   # 获取文件名前缀
        if prefix not in result:
            result[prefix] = []
        result[prefix].append(filename)
    for key in result:
        result[key] = delimiter.join(result[key])
    return result

示例:

filenames = ['file1.txt', 'file2.txt', 'file3.jpg', 'file4.jpg', 'file5.png']
result = group_and_join_filenames(filenames)
print(result)

输出:

{'file1': 'file1.txt', 'file2': 'file2.txt', 'file3': 'file3.jpg', 'file4': 'file4.jpg', 'file5': 'file5.png'}