Is reverse reading possible?
Ivo
Python at ivonet.nl
Sun Mar 14 15:10:26 EST 2004
Please explain a bit more...
Can you tell me more about the lay-out of the file
Is it still formatted per line or per char?
I don't know how to handle chinese because I have never seen it in ASCII
Please give an example...
----- Original Message -----
From: "Anthony Liu" <antonyliu2002 at yahoo.com>
To: "py" <python-list at python.org>
Sent: Sunday, March 14, 2004 8:10 PM
Subject: Re: Is reverse reading possible?
> Jeff and Ivo,
>
> Thank you very much for your solution. Yes, I figure
> out it is easy for an ascii text.
>
> The files (nearly 4M each)I am gonna read are a
> mixture of Chinese and English, where each Chinese
> character has 2 bytes and each English (ASCII) has 1
> byte, although the majority of the texts is Chinese.
>
> So, if we reverse-read it without taking into
> consideration the 2-byte Chinese characters, we are
> gonna get the Chinese characters spelled out in the
> wrong way - unreadable!
>
> So, it might be tedious to read such a text reversely
> unless you have a smarter idea. Do you?
>
>
>
> --- Jeff Epler <jepler at unpythonic.net> wrote:
> > on seekable, byte-oriented binary files, sure.
> >
> > import errno
> >
> > SEEK_SET, SEEK_CUR, SEEK_END = range(3)
> >
> > class Reversed:
> > def __init__(self, f):
> > self.f = f
> > self.f.seek(-1, SEEK_END)
> > self.at_eof = 0
> >
> > def read_byte(self):
> > if self.at_eof: return ''
> > byte = self.f.read(1)
> > try:
> > self.f.seek(-2, SEEK_CUR)
> > except IOError, detail:
> > if detail.errno == errno.EINVAL:
> > self.at_eof = 1
> > else:
> > raise
> > return byte
> >
> > def __iter__(self): return self
> >
> > def next(self):
> > r = self.read_byte()
> > if r == '': raise StopIteration
> > return r
> >
> > >>> "".join(Reversed(file("/etc/redhat-release",
> > "rb")))
> > '\n)worraY( 1 esaeler eroC arodeF'
> >
> > Jeff
>
>
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