如何实现tail -F的pythonic等价物? [英] How to implement a pythonic equivalent of tail -F?

问题描述

在出现某些关键字时，pythonic 的观察方式是什么?

What is the pythonic way of watching the tail end of a growing file for the occurrence of certain keywords?

在 shell 中我可能会说:

In shell I might say:

tail -f "$file" | grep "$string" | while read hit; do
    #stuff
done

推荐答案

嗯，最简单的方法是不断从文件中读取，检查新内容并测试命中率.

Well, the simplest way would be to constantly read from the file, check what's new and test for hits.

import time

def watch(fn, words):
    fp = open(fn, 'r')
    while True:
        new = fp.readline()
        # Once all lines are read this just returns ''
        # until the file changes and a new line appears

        if new:
            for word in words:
                if word in new:
                    yield (word, new)
        else:
            time.sleep(0.5)

fn = 'test.py'
words = ['word']
for hit_word, hit_sentence in watch(fn, words):
    print "Found %r in line: %r" % (hit_word, hit_sentence)

这个带有 readline 的解决方案在您知道您的数据将出现在行中时有效.

This solution with readline works if you know your data will appear in lines.

如果数据是某种流，您需要一个缓冲区，该缓冲区大于您要查找的最大word，并首先填充它.这样会变得有点复杂...

If the data is some sort of stream you need a buffer, larger than the largest word you're looking for, and fill it first. It gets a bit more complicated that way...

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