用Python获取文件的最后n行,类似于尾部 [英] Get last n lines of a file with Python, similar to tail
问题描述
我正在为Web应用程序编写日志文件查看器,为此我想通过日志文件的行分页。所以我需要一个尾巴()
>方法,它可以从底部读取 n
行并支持偏移量。
$ $ $ $ $ $ $ $ $ def尾(f,n,offset = 0)
avg_line_length = 74
to_read = n + offset
while 1:
try:
f.seek( - (avg_line_length * to_read),2)
除了IOError:
#woops。显然文件是小于我们想要的
#退后一步,去开始,而不是
f.seek(0)
pos = f.tell()
lines = f .read()。splitlines()
if len(lines)> = to_read或pos == 0:
return lines [-to_read:offset and -offset or None]
avg_line_length * = 1.3
这是一个合理的方法吗?推荐使用偏移量来记录日志文件的方法是什么?
我最终使用的代码。我认为这是迄今为止最好的:
$ $ $ $ $ $ $ $ $ def尾(f,n,offset =无):
从偏移行的偏移量中读取f行,返回的
值是一个以``(lines,has_more)``形式存在的元组,其中`has_more`是
指示符是`如果文件中有更多的行,则为真。
avg_line_length = 74
to_read = n +(offset or 0)
while 1:
试试:
f.seek( - (avg_line_length * to_read),2)
除了IOError:
#woops。显然文件是小于我们想要的
#退后一步,去开始,而不是
f.seek(0)
pos = f.tell()
lines = f .read()。splitlines()
if len(lines)> = to_read或pos == 0:
return lines [-to_read:offset and -offset or None],\
len(行)> to_read或pos> 0
avg_line_length * = 1.3
I'm writing a log file viewer for a web application and for that I want to paginate through the lines of the log file. The items in the file are line based with the newest item on the bottom.
So I need a tail()
method that can read n
lines from the bottom and supports an offset. What I came up with looks like this:
def tail(f, n, offset=0):
"""Reads a n lines from f with an offset of offset lines."""
avg_line_length = 74
to_read = n + offset
while 1:
try:
f.seek(-(avg_line_length * to_read), 2)
except IOError:
# woops. apparently file is smaller than what we want
# to step back, go to the beginning instead
f.seek(0)
pos = f.tell()
lines = f.read().splitlines()
if len(lines) >= to_read or pos == 0:
return lines[-to_read:offset and -offset or None]
avg_line_length *= 1.3
Is this a reasonable approach? What is the recommended way to tail log files with offsets?
The code I ended up using. I think this is the best so far:
def tail(f, n, offset=None):
"""Reads a n lines from f with an offset of offset lines. The return
value is a tuple in the form ``(lines, has_more)`` where `has_more` is
an indicator that is `True` if there are more lines in the file.
"""
avg_line_length = 74
to_read = n + (offset or 0)
while 1:
try:
f.seek(-(avg_line_length * to_read), 2)
except IOError:
# woops. apparently file is smaller than what we want
# to step back, go to the beginning instead
f.seek(0)
pos = f.tell()
lines = f.read().splitlines()
if len(lines) >= to_read or pos == 0:
return lines[-to_read:offset and -offset or None], \
len(lines) > to_read or pos > 0
avg_line_length *= 1.3
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