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
例如：
obj = open('log','r+')
obj.write('')
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，
obj.close()
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
class file(object):
def close(self): # real signature unknown; restored from __doc__
关闭文件
"""
close() -> None or (perhaps) an integer. Close the file.
Sets data attribute .closed to True. A closed file cannot be used for
further I/O operations. close() may be called more than once without
error. Some kinds of file objects (for example, opened by popen())
may return an exit status upon closing.
"""
def fileno(self): # real signature unknown; restored from __doc__
文件描述符
"""
fileno() -> integer "file descriptor".
This is needed for lower-level file interfaces, such os.read().
"""
return 0
def flush(self): # real signature unknown; restored from __doc__
刷新文件内部缓冲区
""" flush() -> None. Flush the internal I/O buffer. """
pass
def isatty(self): # real signature unknown; restored from __doc__
判断文件是否是同意tty设备
""" isatty() -> true or false. True if the file is connected to a tty device. """
return False
def next(self): # real signature unknown; restored from __doc__
获取下一行数据，不存在，则报错
""" x.next() -> the next value, or raise StopIteration """
pass
def read(self, size=None): # real signature unknown; restored from __doc__
读取指定字节数据 默认读取所有字节
"""
read([size]) -> read at most size bytes, returned as a string.
If the size argument is negative or omitted, read until EOF is reached.
Notice that when in non-blocking mode, less data than what was requested
may be returned, even if no size parameter was given.
"""
pass
def readinto(self): # real signature unknown; restored from __doc__
读取到缓冲区，不要用，将被遗弃
""" readinto() -> Undocumented. Don't use this; it may go away. """
pass
def readline(self, size=None): # real signature unknown; restored from __doc__
仅读取一行数据
"""
readline([size]) -> next line from the file, as a string.
Retain newline. A non-negative size argument limits the maximum
number of bytes to return (an incomplete line may be returned then).
Return an empty string at EOF.
"""
pass
def readlines(self, size=None): # real signature unknown; restored from __doc__
读取所有数据，并根据换行保存值列表
"""
readlines([size]) -> list of strings, each a line from the file.
Call readline() repeatedly and return a list of the lines so read.
The optional size argument, if given, is an approximate bound on the
total number of bytes in the lines returned.
"""
return []
def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
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。
"""
seek(offset[, whence]) -> None. Move to new file position.
Argument offset is a byte count. Optional argument whence defaults to
0 (offset from start of file, offset should be >= 0); other values are 1
(move relative to current position, positive or negative), and 2 (move
relative to end of file, usually negative, although many platforms allow
seeking beyond the end of a file). If the file is opened in text mode,
only offsets returned by tell() are legal. Use of other offsets causes
undefined behavior.
Note that not all file objects are seekable.
"""
pass
def tell(self): # real signature unknown; restored from __doc__
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()
""" tell() -> current file position, an integer (may be a long integer). """
pass
def truncate(self, size=None): # real signature unknown; restored from __doc__
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。
"""
truncate([size]) -> None. Truncate the file to at most size bytes.
Size defaults to the current file position, as returned by tell().
"""
pass
def write(self, p_str): # real signature unknown; restored from __doc__
写内容
"""
write(str) -> None. Write string str to file.
Note that due to buffering, flush() or close() may be needed before
the file on disk reflects the data written.
"""
pass
def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
将一个字符串列表写入文件
"""
writelines(sequence_of_strings) -> None. Write the strings to the file.
Note that newlines are not added. The sequence can be any iterable object
producing strings. This is equivalent to calling write() for each string.
"""
pass
def xreadlines(self): # real signature unknown; restored from __doc__
可用于逐行读取文件，非全部
"""
xreadlines() -> returns self.
要被以下形式替代了
f = file(xxxx)
for line in f:
For backward compatibility. File objects now include the performance
optimizations previously implemented in the xreadlines module.
"""
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：
with open('log','r') as f: ##打开文件的同时，并建立文件句柄
f.write(xxxxxx)
...
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'，‘r’) as obj1, open('log2','w') as obj2:
pass
old.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
log 127.0.0.1 local2
daemon
maxconn 256
log 127.0.0.1 local2 info
defaults
log global
mode http
timeout connect 5000ms
timeout client 50000ms
timeout server 50000ms
option dontlognull listen stats :8888
stats enable
stats uri /admin
stats auth admin:1234 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 1、查
输入：www.oldboy.org
获取当前backend下的所有记录 2、新建
输入：
arg = {
'bakend': 'www.oldboy.org',
'record':{
'server': '100.1.7.9',
'weight': 20,
'maxconn': 30
}
} 3、删除
输入：
arg = {
'bakend': 'www.oldboy.org',
'record':{
'server': '100.1.7.9',
'weight': 20,
'maxconn': 30
}
}
####dome
1 #!/usr/bin/env python
# -*- coding:utf-8 -*-
import json
import os def fetch(backend): #查询
backend_title = 'backend %s' % backend
record_list = [] #先设置一个空列表，用于放置查询出来的数据
with open('ha') as obj:
flag = False
for line in obj: #一行一行读取文件中的数据
line = line.strip() #两边去掉空格
if line == backend_title: #如果这行等于我输入的这行后
flag = True #标志位指为真，为下面的行插入做准备
continue #结束本次循环，下一行就进来了
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
flag = False
break if flag and line:
record_list.append(line) return record_list ##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。
def add(dict_info):
backend = dict_info.get('backend')
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
backend_title = "backend %s" % backend #拼接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']) #拼接记录
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
record_list.append(backend_title)
record_list.append(current_record)
with open('ha') as read_file, open('ha.new', 'w') as write_file: #新生成一个文件，
flag = False
for line in read_file:
write_file.write(line) #从老的配置文件中写入到新文件中
for i in record_list: #
if i.startswith('backend'):
write_file.write(i+'\n')
else:
write_file.write("%s%s\n" % (8*" ", i)) #拼接字符串
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）
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: #找到我们要添加的那一行了，
flag = True
continue
if flag and line_strip.startswith('backend'):
flag = False
#上下部分
if not flag:
write_file.write(line)
else:
#中间部分
if not has_write: #没写过，就写一遍
for i in record_list:
if i.startswith('backend'):
write_file.write(i+'\n')
else:#否则 写过就不在写了，
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') if __name__ == '__main__':
"""
print '1、获取；2、添加；3、删除'
num = raw_input('请输入序号：')
data = raw_input('请输入内容：')
if num == '1':
fetch(data)
else:
dict_data = json.loads(data) 利用json转换成字典
if num == '2':
add(dict_data)
elif num == '3':
remove(dict_data)
else:
pass
"""
#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)
2、文件处理中xreadlines的内部是如何实现的呢？