Python下的tail库 tail.py修正版
尊重作者，贴上链接，
第一版作者：一个斯里兰卡程序员
https://github.com/kasun/python-tail
第二版作者：
http://www.cnblogs.com/bufferfly/p/4878688.html
但其中有bug，修复后代码见下文
bug描述：
1、在 _size = os.path.getsize(self.tailed_file) 处， 可能有文件不存在的异常，需要正确处理一下，否则运行时间长了，会导致程序退出
修复后的代码，见wait_file_get_size函数
#!-*- coding: utf-8 -*-
################################################################################
#
# Copyright (c) 2015 XX.com, Inc. All Rights Reserved
#
################################################################################
################################################################################
# This module provide ...
# Third libs those depend on:
################################################################################
"""
Compiler Python 2.7.10
Authors: [email protected]
Date: 2017-07-31
Desc:类似于tail命令的python lib ， 可以注册一个回调函数，每读取一行，则触发一次回调
Modify: 1、修复一个bug， _size=os.path.getsize 那一行，会出现异常，提示文件不存在，加了try和等待
"""
"""SYS LIBS
"""
import os
import re
import sys
import time
"""THIRD LIBS
"""
try:
# import the third libs there.
pass
except ImportError as e:
print e
os._exit(-1)
"""CUSTOM libs
Strongly recommend using abs path when using custmo libs.
"""
# Good behaviors.
# It means refusing called like from xxx import *
# When `__all__` is []
__all__ = []
reload(sys)
sys.setdefaultencoding('utf-8')
def send_error(msg):
""" Send error to email.
"""
print msg
#********************************************************
#* Global defines start. *
#********************************************************
#********************************************************
#* Global defines end. *
#********************************************************
class Tail(object):
"""
Python-Tail - Unix tail follow implementation in Python.
python-tail can be used to monitor changes to a file.
Example:
import tail
# Create a tail instance
t = tail.Tail('file-to-be-followed')
# Register a callback function to be called when a new line is found in the followed file.
# If no callback function is registerd, new lines would be printed to standard out.
t.register_callback(callback_function)
# Follow the file with 5 seconds as sleep time between iterations.
# If sleep time is not provided 1 second is used as the default time.
t.follow(s=5)
"""
''' Represents a tail command. '''
def __init__(self, tailed_file):
''' Initiate a Tail instance.
Check for file validity, assigns callback function to standard out.
Arguments:
tailed_file - File to be followed. '''
self.check_file_validity(tailed_file)
self.tailed_file = tailed_file
self.callback = sys.stdout.write
self.try_count = 0
try:
self.file_ = open(self.tailed_file, "r")
self.size = os.path.getsize(self.tailed_file)
# Go to the end of file
self.file_.seek(0, 2)
except:
raise
def reload_tailed_file(self):
""" Reload tailed file when it be empty be `echo "" > tailed file`, or
segmentated by logrotate.
"""
try:
self.file_ = open(self.tailed_file, "r")
self.size = os.path.getsize(self.tailed_file)
# Go to the head of file
self.file_.seek(0, 1)
return True
except:
return False
def wait_file_get_size(self, file):
while 1:
try:
_size = os.path.getsize(self.tailed_file)
return _size
except:
print("Error when getsize of tailed_file")
time.sleep(0.1)
continue
def follow(self, s=0.01):
""" Do a tail follow. If a callback function is registered it is called with every new line.
Else printed to standard out.
Arguments:
s - Number of seconds to wait between each iteration; Defaults to 1. """
while True:
_size = self.wait_file_get_size(self.tailed_file)
if _size < self.size:
while self.try_count < 10:
if not self.reload_tailed_file():
self.try_count += 1
else:
self.try_count = 0
self.size = os.path.getsize(self.tailed_file)
break
time.sleep(0.1)
if self.try_count == 10:
raise Exception("Open %s failed after try 10 times" % self.tailed_file)
else:
self.size = _size
curr_position = self.file_.tell()
line = self.file_.readline()
if not line:
self.file_.seek(curr_position)
elif not line.endswith("\n"):
self.file_.seek(curr_position)
else:
self.callback(line)
time.sleep(s)
def register_callback(self, func):
""" Overrides default callback function to provided function. """
self.callback = func
def check_file_validity(self, file_):
""" Check whether the a given file exists, readable and is a file """
if not os.access(file_, os.F_OK):
raise TailError("File '%s' does not exist" % (file_))
if not os.access(file_, os.R_OK):
raise TailError("File '%s' not readable" % (file_))
if os.path.isdir(file_):
raise TailError("File '%s' is a directory" % (file_))
class TailError(Exception):
""" Custom error type.
"""
def __init__(self, msg):
""" Init.
"""
self.message = msg
def __str__(self):
""" str.
"""
return self.message
if __name__ == '__main__':
t = Tail(sys.argv[1])
def print_msg(msg):
print msg
#print msg.split(']')[0]
t.register_callback(filter_and_post)
t.follow()
""" vim: set ts=4 sw=4 sts=4 tw=100 et: """