How to process huge text files that contain EOF / Ctrl-Z characters using Python on Windows?

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Question :

How to process huge text files that contain EOF / Ctrl-Z characters using Python on Windows?

I have a number of large comma-delimited text files (the biggest is about 15GB) that I need to process using a Python script. The problem is that the files sporadically contain DOS EOF (Ctrl-Z) characters in the middle of them. (Don’t ask me why, I didn’t generate them.) The other problem is that the files are on a Windows machine.

On Windows, when my script encounters one of these characters, it assumes it is at the end of the file and stops processing. For various reasons, I am not allowed to copy the files to any other machine. But I still need to process them.

Here are my ideas so far:

  1. Read the file in binary mode, throwing out bytes that equal chr(26). This would work, but it would take approximately forever.
  2. Use something like sed to eliminate the EOF characters. Unfortunately, as far as I can tell, sed on Windows has the same problem and will quit when it sees the EOF.
  3. Use some kind of Notepad program and do a find-and-replace. But it turns out that Notepad-type programs don’t cope well with 15GB files.

My IDEAL solution would be some way to just read the file as text and simply ignore the Ctrl-Z characters. Is there a reasonable way to accomplish this?

Asked By: Joel

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Answer #1:

It’s easy to use Python to delete the DOS EOF chars; for example,

def delete_eof(fin, fout):
    BUFSIZE = 2**15
    EOFCHAR = chr(26)
    data = fin.read(BUFSIZE)
    while data:
        fout.write(data.translate(None, EOFCHAR))
        data = fin.read(BUFSIZE)

import sys
ipath = sys.argv[1]
opath = ipath + ".new"
with open(ipath, "rb") as fin, open(opath, "wb") as fout:
    delete_eof(fin, fout)

That takes a file path as its first argument, and copies the file but without chr(26) bytes to the same file path with .new appended. Fiddle to taste.

By the way, are you sure that DOS EOF characters are your only problem? It’s hard to conceive of a sane way in which they could end up in files intended to be treated as text files.

Answered By: Tim Peters

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