Python之路:Python 基础(三)-文件操作
操作文件时,一般需要经历如下步骤:
- 打开文件
- 操作文件
一、打开文件
文件句柄 = file('文件路径', '模式') # 还有一种方法open
例1、创建文件
f = file('myfile.txt','w') w、r、a 'rb'二进制读文件
f.write('Hello world!')
f.close( )
例2、遍历文件内容 (一行一行的读内文件内容)
a = file('myfile.txt')
for line in a.readlines():
print line
a.close( )
例3、追加
f = file('test1.txt','a')
f = write('append to the end')
f.close( )
例4、文件内容替换
for line in fileinput.input('test1.txt',inplace=1,backup='.bak'): #表示把匹配的内容写到文件中,并先备份原文件
line = line.replace('oldtext','newtext')
print line
例5、 with open('test1.txt','r+') as f: 相当于‘例3’
二、打开文件的模式有:
- r,只读模式(默认)。
- w,只写模式。【不可读;不存在则创建;存在则删除内容;】
- a,追加模式。【可读; 不存在则创建;存在则只追加内容;】
"+" 表示可以同时读写某个文件
- r+,可读写文件。【可读;可写;可追加】
- w+,无意义
- a+,同a
"U"表示在读取时,可以将 \r \n \r\n自动转换成 \n (与 r 或 r+ 模式同使用)
- rU
- r+U
"b"表示处理二进制文件(如:FTP发送上传ISO镜像文件,linux可忽略,windows处理二进制文件时需标注)
- rb
- wb
- ab
>>> dir(file)
['__class__', '__delattr__', '__doc__', '__enter__', '__exit__', '__format__', '__getattribute__', '__hash__', '__init__', '__iter__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'close', 'closed', 'encoding', 'errors', 'fileno', 'flush', 'isatty', 'mode', 'name', 'newlines', 'next', 'read', 'readinto', 'readline', 'readlines', 'seek', 'softspace', 'tell', 'truncate', 'write', 'writelines', 'xreadlines']
三、with
为了避免打开文件后忘记关闭,可以通过管理上下文,即:
with open('log','r') as f: ...
如此方式,当with代码块执行完毕时,内部会自动关闭并释放文件资源。
在Python 2.7 后,with又支持同时对多个文件的上下文进行管理,即:
with open('log1') as obj1, open('log2') as obj2: pass
四、修改配置文件
原文件:
global log 127.0.0.1 local2 daemon maxconn 256 log 127.0.0.1 local2 info frontend oldboy.org bind 0.0.0.0:80 option httplog option httpclose option forwardfor log global acl www hdr_reg(host) -i www.oldboy.org use_backend www.oldboy.org if www backend www.oldboy.org server 100.1.7.9 100.1.7.9 weight 20 maxconn 3000
需求:
1、查 输入:www.oldboy.org 获取当前backend下的所有记录 2、新建:backend字段 3、删除:backend字段
代码如下:
#!/usr/bin/env python # -*- coding:utf-8 -*- import json import os def fetch(backend): backend_title = 'backend %s' % backend record_list = [] with open('ha') as obj: flag = False for line in obj: line = line.strip() if line == backend_title: flag = True continue if flag and line.startswith('backend'): flag = False break if flag and line: record_list.append(line) return record_list def add(dict_info): backend = dict_info.get('backend') record_list = fetch(backend) backend_title = "backend %s" % backend current_record = "server %s %s weight %d maxconn %d" % (dict_info['record']['server'], dict_info['record']['server'], dict_info['record']['weight'], dict_info['record']['maxconn']) if not record_list: record_list.append(backend_title) record_list.append(current_record) with open('ha') as read_file, open('ha.new', 'w') as write_file: flag = False for line in read_file: write_file.write(line) for i in record_list: if i.startswith('backend'): write_file.write(i+'\n') else: write_file.write("%s%s\n" % (8*" ", i)) else: record_list.insert(0, backend_title) if current_record not in record_list: record_list.append(current_record) with open('ha') as read_file, open('ha.new', 'w') as write_file: flag = False has_write = False for line in read_file: line_strip = line.strip() if line_strip == backend_title: flag = True continue if flag and line_strip.startswith('backend'): flag = False if not flag: write_file.write(line) else: if not has_write: for i in record_list: if i.startswith('backend'): write_file.write(i+'\n') else: write_file.write("%s%s\n" % (8*" ", i)) has_write = True os.rename('ha','ha.bak') os.rename('ha.new','ha') def remove(dict_info): backend = dict_info.get('backend') record_list = fetch(backend) backend_title = "backend %s" % backend current_record = "server %s %s weight %d maxconn %d" % (dict_info['record']['server'], dict_info['record']['server'], dict_info['record']['weight'], dict_info['record']['maxconn']) if not record_list: return else: if current_record not in record_list: return else: del record_list[record_list.index(current_record)] if len(record_list) > 0: record_list.insert(0, backend_title) with open('ha') as read_file, open('ha.new', 'w') as write_file: flag = False has_write = False for line in read_file: line_strip = line.strip() if line_strip == backend_title: flag = True continue if flag and line_strip.startswith('backend'): flag = False if not flag: write_file.write(line) else: if not has_write: for i in record_list: if i.startswith('backend'): write_file.write(i+'\n') else: write_file.write("%s%s\n" % (8*" ", i)) has_write = True os.rename('ha','ha.bak') os.rename('ha.new','ha') data = "www.oldboy.org" fetch(data) data = '{"backend": "tettst.oldboy.org","record":{"server": "100.1.7.90","weight": 20,"maxconn": 30}}' dict_data = json.loads(data) add(dict_data) remove(dict_data)