文件(file)操作
创建文件
verse.txt:
床前明月光 疑是地上霜
open(path(文件路径),mode(模式:r/r+[读],w/w+[写],a/a+[追加])):返回文件句柄(对象)
verse_file = open('verse.txt','r',encoding="utf-8")
r/r+[读],w/w+[写],a/a+[追加]的区别
| mode | 可做操作 | 若文件不存在 | 是否覆盖 |
| r | 只读 | 报错 | - |
| r+ | 读写 | 报错 | 是 |
| w | 只写 | 创建 | 是 |
| w+ | 读写 | 创建 | 是 |
| a | 只写 | 创建 | 追加 |
| a+ | 读写 | 创建 | 追加 |
readlines():获取所有行,返回list
verse_file = open('verse.txt','r',encoding="utf-8")
print(verse_file.readlines())
verse_file.close()
#result:
#['床前明月光\n', '疑是地上霜']
read():读取所有字符,返回string
verse_file = open('verse.txt','r',encoding="utf-8")
print(verse_file.read())
verse_file.close()
#result:
# 床前明月光
# 疑是地上霜
遍历文件最优法(懒加载)
verse_file = open('verse.txt','r',encoding="utf-8")
for row in verse_file:
print(row.strip())
#result:
# 床前明月光
# 疑是地上霜
write():写入.当mode为'w'[写]时,会清空之前的内容再写入;当mode为'a'[追加]时,会在原来基础上继续追加写入
verse_file = open('verse.txt','w',encoding="utf-8")
input_str = '举头望明月\n低头思故乡'
verse_file.write(input_str)
verse_file.close()
"""
verse.txt:
举头望明月
低头思故乡
"""
verse_file = open('verse.txt','a',encoding="utf-8")
input_str = '举头望明月\n低头思故乡'
verse_file.write(input_str)
verse_file.close()
"""
verse.txt:
床前明月光
疑是地上霜举头望明月
低头思故乡
"""
seek(position):定位光标位置
verse_file = open('verse.txt','r',encoding="utf-8")
verse_file.seek(6)#utf-8中一个中文字符占3个字节
print(verse_file.read())
verse_file.close()
"""
verse.txt:
明月光
疑是地上霜
"""
tell():获取光标位置
verse_file = open('verse.txt','r',encoding="utf-8")
verse_file.seek(6)
print(verse_file.tell());#result:6
练习
多级目录文件持久化增删改查
address.dic:
{}
file.py:
file = open('address.dic', 'r', encoding='utf8')
history_list = []
address_dic = eval(file.read())
while True:
print('---当前地址---')
for current in address_dic:
print(current)
choose = input('请选择---0:返回上一层,1:新增,2:删除,3:修改,4:查询,5:保存退出:')
':
if history_list:
address_dic = history_list.pop();
':
insert_name = input('请输入新增项名称:')
if insert_name in address_dic:
print('新增失败!该名称项已存在!')
continue;
else:
address_dic[insert_name] = {}
':
delete_name = input('请输入删除项名称:')
if delete_name not in address_dic:
print('删除失败!该名称项不存在!')
continue;
else:
del address_dic[delete_name];
':
modify_name = input('请输入修改项名称:')
if modify_name not in address_dic:
print('修改失败!该名称项不存在!')
continue;
else:
modify_to_name = input('请输入修改后的名称:')
modify_value = address_dic[modify_name];
address_dic[modify_to_name] = modify_value
del address_dic[modify_name]
':
select_name = input("请输入查询项名称:")
if select_name not in address_dic:
print('查询失败!该名称项不存在!')
continue;
else:
history_list.append(address_dic)
address_dic = address_dic[select_name]
if not address_dic:
print('当前无地址')
':
file = open('address.dic', 'w+', encoding='utf8')
if history_list:
file.write(str(history_list[0]))
else:
file.write(str(address_dic))
file.close();
break;
else:
print("输入错误")
运行结果:
address.dic:
{'湖北': {'武汉': {}}, '广东': {'深圳': {}}}
扩展
eval(str):可将对应格式字符串转成相应类型对象.例:
dic_str = "{'1':'a','2':'b'}"
list_str = "['1','2','3']"
dic = eval(dic_str)
list = eval(list_str)
print(dic,type(dic))
print(list,type(list))
#result:
# {'1': 'a', '2': 'b'} <class 'dict'>
# ['1', '2', '3'] <class 'list'>
with:类似C#中Using块,当前块执行完释放对象.下面两块代码等价.
with open("test",'r') as file:
file.read();
file = open("test",'r')
file.read()
file.close()