0

我正在尝试从Python 中的Common Crawl解析 .warc 文件。

由于文件很大，我想从前几条记录的样本/子集开始。

如何截断文件以仅包含前 X 行，同时保留现有的换行符/回车符？

这是我已经尝试过的：

  1. head -n 250 oldfile > newfile这删除了解析文件所需的一些返回。如果我尝试在我的 Hadoop 作业中使用这个文件（使用warc包读取它），这是我得到的错误：

      Traceback (most recent call last):
      File "test.py", line 46, in <module>
        TagGrabber.run()
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/job.py", line 461, in run
        mr_job.execute()
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/job.py", line 479, in execute
        super(MRJob, self).execute()
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/launch.py", line 151, in execute
        self.run_job()
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/launch.py", line 214, in run_job
        runner.run()
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/runner.py", line 464, in run
        self._run()
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/sim.py", line 173, in _run
        self._invoke_step(step_num, 'mapper')
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/sim.py", line 264, in _invoke_step
        self.per_step_runner_finish(step_num)
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/local.py", line 152, in per_step_runner_finish
        self._wait_for_process(proc_dict, step_num)
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/mrjob/local.py", line 268, in _wait_for_process
        (proc_dict['args'], returncode, ''.join(tb_lines)))
    Exception: Command ['sh', '-ex', 'setup-wrapper.sh', '/var/cc-mrjob/venv/bin/python', 'test.py', '--step-num=0', '--mapper', '/tmp/test.root.20150520.071726.549519/input_part-00000'] returned non-zero exit status 1:
    Traceback (most recent call last):
      File "test.py", line 46, in <module>
        TagGrabber.run()
      File "/tmp/test.root.20150520.071726.549519/job_local_dir/0/mapper/0/mrjob.tar.gz/mrjob/job.py", line 461, in run
        mr_job.execute()
      File "/tmp/test.root.20150520.071726.549519/job_local_dir/0/mapper/0/mrjob.tar.gz/mrjob/job.py", line 470, in execute
        self.run_mapper(self.options.step_num)
      File "/tmp/test.root.20150520.071726.549519/job_local_dir/0/mapper/0/mrjob.tar.gz/mrjob/job.py", line 535, in run_mapper
        for out_key, out_value in mapper(key, value) or ():
      File "/var/cc-mrjob/mrcc.py", line 33, in mapper
        for i, record in enumerate(f):
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/warc/warc.py", line 390, in __iter__
        record = self.read_record()
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/warc/warc.py", line 373, in read_record
        header = self.read_header(fileobj)
      File "/var/cc-mrjob/venv/local/lib/python2.7/site-packages/warc/warc.py", line 331, in read_header
        raise IOError("Bad version line: %r" % version_line)
    IOError: Bad version line: 'WARC/1.0\n'

  2. 与 #1 相同，但使用tail命令

  3. 与 #1 相同，但使用tror sedafter 替换任何丢失的换行符或^M（回车符）字符。这会导致warc包仍然抱怨预期的回车或换行符没有到位。
  4. unix2dos oldfile
4

1 回答 1

1

由于 .warc 文件也可能包含二进制数据，因此很难正确处理换行符。截断也可能会产生损坏的 .warc 文件，因为例如 python 库相信 Content-Length 标头是有效的。

warc python 库一次只从 .warc 文件中读取一条记录（避免一次将整个文件读取到内存中），因此可以仅使用 python 处理子集。例如：

import warc
from itertools import islice

N = 10
warc_file = warc.open('/path/to/file.warc')
for record in islice(warc_file, N):
    do_stuff_with(record)
于 2015-05-21T10:07:00.457 回答