python获取目录下指定后缀名的文件

import os
all_file_list =[]
## 获取路径下的png文件
def get_all_filepath(dir):
    parents = os.listdir(dir)
    for parent in parents:
        child = os.path.join(dir,parent)
        if os.path.isdir(child):
            get_all_filepath(child)
        else:
            suffix = os.path.splitext(child)[1]
            #print(suffix)
            if suffix ==".png":
                all_file_list.append(child)