Why Python does not see all the rows in a file?

问题

I count number of rows (lines) in a file using Python in the following method:

n = 0
for line in file('input.txt'):
   n += 1
print n

I run this script under Windows.

Then I count the number of rows in the same file using Unix command:

wc -l input.txt

Counting with Unix command gives a significantly larger number of rows.

So, my question is: Why Python does not see all the rows in the file? Or is it a question of definition?

回答1:

You most likely have a file with one or more DOS EOF (CTRL-Z) characters in it, ASCII codepoint 0x1A. When Windows opens a file in text mode, it'll still honour the old DOS semantics and end a file whenever it reads that character. See Line reading chokes on 0x1A.

Only by opening a file in binary mode can you bypass this behaviour. To do so and still count lines, you have two options:

• read in chunks, then count the number of line separators in each chunk:

  def bufcount(filename, linesep=os.linesep, buf_size=2 ** 15):
      lines = 0
      with open(filename, 'rb') as f:
          last = ''
          for buf in iter(f.read, ''):
              lines += buf.count(linesep)
              if last and last + buf[0] == linesep:
                  # count line separators straddling a boundary
                  lines += 1
              if len(linesep) > 1:
                  last = buf[-1]
      return lines
  

  Take into account that on Windows os.linesep is set to \r\n, adjust as needed for your file; in binary mode line separators are not translated to \n.

• Use io.open(); the io set of file objects open the file in binary mode always, then do the translations themselves:

  import io
  
  with io.open(filename) as f:
      lines = sum(1 for line in f)
  

来源：https://stackoverflow.com/questions/36727446/why-python-does-not-see-all-the-rows-in-a-file