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
文件句柄 = file('文件路径', '模式')
注：python中打开文件有两种方式，即：open(...) 和 file(...) ，本质上前者在内部会调用后者来进行文件操作，推荐使用 open。 open会自己在Python中找。
打开文件时，需要指定文件路径和以何等方式打开文件，打开后，即可获取该文件句柄，日后通过此文件句柄对该文件操作。
打开文件的模式有：
- r，只读模式（默认）。
- w，只写模式。【不可读，也就是重写这个文件，首先就是先清空原来的内容，然后重写；不存在则创建；存在则删除内容；】
- a，追加模式。【可读，可写；不存在则创建；存在则只追加内容；】 默认指针应该在文件的最后端。
"+" 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+，写读 等同于w
- a+，同a
1 例如：
2 obj = open('log','r+')
3 obj.write('0000')
4 obj.truncate() 默认截断数据，根据当前指针截断，如果truncate(5),就只保留前5个，
5 obj.close()
6 在r+的情况下，如果要write，就是文件指针在最开始，然后0000去一个一个替换。"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），只能与r一起用。
- 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
二、操作操作
1 class file(object):
2
3 def close(self): # real signature unknown; restored from __doc__
4 关闭文件
5 """
6 close() -> None or (perhaps) an integer. Close the file.
7
8 Sets data attribute .closed to True. A closed file cannot be used for
9 further I/O operations. close() may be called more than once without
10 error. Some kinds of file objects (for example, opened by popen())
11 may return an exit status upon closing.
12 """
13
14 def fileno(self): # real signature unknown; restored from __doc__
15 文件描述符
16 """
17 fileno() -> integer "file descriptor".
18
19 This is needed for lower-level file interfaces, such os.read().
20 """
21 return 0
22
23 def flush(self): # real signature unknown; restored from __doc__
24 刷新文件内部缓冲区
25 """ flush() -> None. Flush the internal I/O buffer. """
26 pass
27
28
29 def isatty(self): # real signature unknown; restored from __doc__
30 判断文件是否是同意tty设备
31 """ isatty() -> true or false. True if the file is connected to a tty device. """
32 return False
33
34
35 def next(self): # real signature unknown; restored from __doc__
36 获取下一行数据，不存在，则报错
37 """ x.next() -> the next value, or raise StopIteration """
38 pass
39
40 def read(self, size=None): # real signature unknown; restored from __doc__
41 读取指定字节数据 默认读取所有字节
42 """
43 read([size]) -> read at most size bytes, returned as a string.
44
45 If the size argument is negative or omitted, read until EOF is reached.
46 Notice that when in non-blocking mode, less data than what was requested
47 may be returned, even if no size parameter was given.
48 """
49 pass
50
51 def readinto(self): # real signature unknown; restored from __doc__
52 读取到缓冲区，不要用，将被遗弃
53 """ readinto() -> Undocumented. Don't use this; it may go away. """
54 pass
55
56 def readline(self, size=None): # real signature unknown; restored from __doc__
57 仅读取一行数据
58 """
59 readline([size]) -> next line from the file, as a string.
60
61 Retain newline. A non-negative size argument limits the maximum
62 number of bytes to return (an incomplete line may be returned then).
63 Return an empty string at EOF.
64 """
65 pass
66
67 def readlines(self, size=None): # real signature unknown; restored from __doc__
68 读取所有数据，并根据换行保存值列表
69 """
70 readlines([size]) -> list of strings, each a line from the file.
71
72 Call readline() repeatedly and return a list of the lines so read.
73 The optional size argument, if given, is an approximate bound on the
74 total number of bytes in the lines returned.
75 """
76 return []
77
78 def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
79 指定文件中指针位置 seek(5) 指定文件指针从第5个字符开始读取文件。
80 """
81 seek(offset[, whence]) -> None. Move to new file position.
82
83 Argument offset is a byte count. Optional argument whence defaults to
84 0 (offset from start of file, offset should be >= 0); other values are 1
85 (move relative to current position, positive or negative), and 2 (move
86 relative to end of file, usually negative, although many platforms allow
87 seeking beyond the end of a file). If the file is opened in text mode,
88 only offsets returned by tell() are legal. Use of other offsets causes
89 undefined behavior.
90 Note that not all file objects are seekable.
91 """
92 pass
93
94 def tell(self): # real signature unknown; restored from __doc__
95 获取当前指针位置，也就是一个文件开始从哪开始读。
例如： obj = open('logs','r')
obj.seek(5) ###把文件指针放到第5个字节，也就是从第5个字节开始读
print obj.tell()#获取当前的指针
print obj.read()
print obj.tell()
obj.close()
96 """ tell() -> current file position, an integer (may be a long integer). """
97 pass
98
99 def truncate(self, size=None): # real signature unknown; restored from __doc__
100 截断数据，仅保留指定之前数据.默认情况下指针在哪，后面的就全部不要了。
101 """
102 truncate([size]) -> None. Truncate the file to at most size bytes.
103
104 Size defaults to the current file position, as returned by tell().
105 """
106 pass
107
108 def write(self, p_str): # real signature unknown; restored from __doc__
109 写内容
110 """
111 write(str) -> None. Write string str to file.
112
113 Note that due to buffering, flush() or close() may be needed before
114 the file on disk reflects the data written.
115 """
116 pass
117
118 def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
119 将一个字符串列表写入文件
120 """
121 writelines(sequence_of_strings) -> None. Write the strings to the file.
122
123 Note that newlines are not added. The sequence can be any iterable object
124 producing strings. This is equivalent to calling write() for each string.
125 """
126 pass
127
128 def xreadlines(self): # real signature unknown; restored from __doc__
129 可用于逐行读取文件，非全部
130 """
131 xreadlines() -> returns self.
132 要被以下形式替代了
f = file(xxxx)
for line in f:
133 For backward compatibility. File objects now include the performance
134 optimizations previously implemented in the xreadlines module.
135 """
136 pass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：
1 with open('log','r') as f: ##打开文件的同时，并建立文件句柄
2 f.write(xxxxxx)
3 ...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：
1 with open('log1'，‘r’) as obj1, open('log2','w') as obj2:
2 passold.conf ===>r new.conf w,
with open('log1','r') as obj1,open('log2','w') as obj2;
for line obj1:
new_line = line.replace('10.0.0.1','10.0.0.2')
obj2.write(new_line)四、那么问题来了...
1、如何在线上环境优雅的修改配置文件?
####原配置文件
1 global
2 log 127.0.0.1 local2
3 daemon
4 maxconn 256
5 log 127.0.0.1 local2 info
6 defaults
7 log global
8 mode http
9 timeout connect 5000ms
10 timeout client 50000ms
11 timeout server 50000ms
12 option dontlognull
13
14 listen stats :8888
15 stats enable
16 stats uri /admin
17 stats auth admin:1234
18
19 frontend oldboy.org
20 bind 0.0.0.0:80
21 option httplog
22 option httpclose
23 option forwardfor
24 log global
25 acl www hdr_reg(host) -i www.oldboy.org
26 use_backend www.oldboy.org if www
27
28 backend www.oldboy.org
29 server 100.1.7.9 100.1.7.9 weight 20 maxconn 3000###需求
1 1、查
2 输入：www.oldboy.org
3 获取当前backend下的所有记录
4
5 2、新建
6 输入：
7 arg = {
8 'bakend': 'www.oldboy.org',
9 'record':{
10 'server': '100.1.7.9',
11 'weight': 20,
12 'maxconn': 30
13 }
14 }
15
16 3、删除
17 输入：
18 arg = {
19 'bakend': 'www.oldboy.org',
20 'record':{
21 'server': '100.1.7.9',
22 'weight': 20,
23 'maxconn': 30
24 }
25 }####dome
1 #!/usr/bin/env python
2 # -*- coding:utf-8 -*-
3 import json
4 import os
5
6
7 def fetch(backend): #查询
8 backend_title = 'backend %s' % backend
9 record_list = [] #先设置一个空列表，用于放置查询出来的数据
10 with open('ha') as obj:
11 flag = False
12 for line in obj: #一行一行读取文件中的数据
13 line = line.strip() #两边去掉空格
14 if line == backend_title: #如果这行等于我输入的这行后
15 flag = True #标志位指为真，为下面的行插入做准备
16 continue #结束本次循环，下一行就进来了
17 if flag and line.startswith('backend'):#判断当前行是backend开头的，并且flag等于ture,才终止取值了
18 flag = False
19 break
20
21 if flag and line:
22 record_list.append(line)
23
24 return record_list
25
26 ##添加一条记录，可以这么去实现，我新加一个列表来拼接我要修改的数据
其他的都按照原来的方式一条一条写入。
找到www.oldboy.org ,添加一条（如存在，不操作）
1 找到制定backend的下所有记录：
2 处理记录（原来存在记录，就不定，原来不存在的，就插到列表中）
3写文件了。
27 def add(dict_info):
28 backend = dict_info.get('backend')
29 record_list = fetch(backend) #获取指定backend下的所有记录，用的是上面的字定义的函数
30 backend_title = "backend %s" % backend #拼接backend
31 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']) #拼接记录
32 if not record_list: #不存在，要添加backend和值，只需在原文件最后添加即可
33 record_list.append(backend_title)
34 record_list.append(current_record)
35 with open('ha') as read_file, open('ha.new', 'w') as write_file: #新生成一个文件，
36 flag = False
37 for line in read_file:
38 write_file.write(line) #从老的配置文件中写入到新文件中
39 for i in record_list: #
40 if i.startswith('backend'):
41 write_file.write(i+'\n')
42 else:
43 write_file.write("%s%s\n" % (8*" ", i)) #拼接字符串
44 else: #存在backend,只需在添加记录（又分为两种情况，一种是已经存在这条记录了，我们就不动，要是不存在，就添加）
45 record_list.insert(0, backend_title)
46 if current_record not in record_list:
47 record_list.append(current_record)
48
49 with open('ha') as read_file, open('ha.new', 'w') as write_file:
50 flag = False
51 has_write = False
52 for line in read_file:
53 line_strip = line.strip()
54 if line_strip == backend_title: #找到我们要添加的那一行了，
55 flag = True
56 continue
57 if flag and line_strip.startswith('backend'):
58 flag = False
#上下部分
59 if not flag:
60 write_file.write(line)
61 else:
#中间部分
62 if not has_write: #没写过，就写一遍
63 for i in record_list:
64 if i.startswith('backend'):
65 write_file.write(i+'\n')
66 else:#否则 写过就不在写了，
67 write_file.write("%s%s\n" % (8*" ", i))
68 has_write = True
69 os.rename('ha','ha.bak')
70 os.rename('ha.new','ha')
71
72
73 def remove(dict_info):
74 backend = dict_info.get('backend')
75 record_list = fetch(backend)
76 backend_title = "backend %s" % backend
77 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'])
78 if not record_list:
79 return
80 else:
81 if current_record not in record_list:
82 return
83 else:
84 del record_list[record_list.index(current_record)]
85 if len(record_list) > 0:
86 record_list.insert(0, backend_title)
87 with open('ha') as read_file, open('ha.new', 'w') as write_file:
88 flag = False
89 has_write = False
90 for line in read_file:
91 line_strip = line.strip()
92 if line_strip == backend_title:
93 flag = True
94 continue
95 if flag and line_strip.startswith('backend'):
96 flag = False
97 if not flag:
98 write_file.write(line)
99 else:
100 if not has_write:
101 for i in record_list:
102 if i.startswith('backend'):
103 write_file.write(i+'\n')
104 else:
105 write_file.write("%s%s\n" % (8*" ", i))
106 has_write = True
107 os.rename('ha','ha.bak')
108 os.rename('ha.new','ha')
109
110 if __name__ == '__main__':
111 """
112 print '1、获取；2、添加；3、删除'
113 num = raw_input('请输入序号：')
114 data = raw_input('请输入内容：')
115 if num == '1':
116 fetch(data)
117 else:
118 dict_data = json.loads(data) 利用json转换成字典
119 if num == '2':
120 add(dict_data)
121 elif num == '3':
122 remove(dict_data)
123 else:
124 pass
125 """
126 #data = "www.oldboy.org"
127 #fetch(data)
128 #data = '{"backend": "tettst.oldboy.org","record":{"server": "100.1.7.90","weight": 20,"maxconn": 30}}'
129 #dict_data = json.loads(data)
130 #add(dict_data)
131 #remove(dict_data)2、文件处理中xreadlines的内部是如何实现的呢？
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