Python内置函数
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内置函数 一
详细见python文档，猛击这里
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
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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。
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；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+，写读
- 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
二、操作操作
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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 """ 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(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 """ 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 """ 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. 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：
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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：
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with open(\'log1\') as obj1, open(\'log2\') as obj2: pass |
四、那么问题来了...
1、如何在线上环境优雅的修改配置文件?
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
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
}
}
#!/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\')
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)
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？
自定义函数
一、背景
在学习函数之前，一直遵循：面向过程编程，即：根据业务逻辑从上到下实现功能，其往往用一长段代码来实现指定功能，开发过程中最常见的操作就是粘贴复制，也就是将之前实现的代码块复制到现需功能处，如下
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while True： if cpu利用率 > 90%: #发送邮件提醒 连接邮箱服务器 发送邮件 关闭连接 if 硬盘使用空间 > 90%: #发送邮件提醒 连接邮箱服务器 发送邮件 关闭连接 if 内存占用 > 80%: #发送邮件提醒 连接邮箱服务器 发送邮件 关闭连接 |
腚眼一看上述代码，if条件语句下的内容可以被提取出来公用，如下：
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