python工具函数

# 创建一个目录。若该目录存在，则删除该目录并重新创建
import shutil

def make_empty_dir(dir_path):
    try:
        shutil.rmtree(dir_path)
    except:
        pass
    os.mkdir(dir_path)

# 将（中文）字典保存为json文件
import json

d = {'浙江':['杭州','宁波','温州'],
     '江苏':['南京','苏州','无锡'],
     '福建':['福州','厦门','泉州']}

with open('d:/sample.json', 'w', encoding='utf-8-sig') as f:
    json_data = json.dumps(d, indent=4, ensure_ascii=False)
    f.write(json_data)

# 求集合(实际是列表)所有子集
def PowerSetsRecursive(items):
    """Use recursive call to return all subsets of items, include empty set"""
    if len(items) == 0:
        return [[]]
    subsets = []
    first_elt = items[0] #first element
    rest_list = items[1:]   
    for partial_sebset in PowerSetsRecursive(rest_list):
        subsets.append(partial_sebset)
        next_subset = partial_sebset[:] +[first_elt]
        subsets.append(next_subset)
    return subsets