Re: [Jython-users] Binary data changed in read

[John M. <joh...@ya...>]

Yes, binary mode of course.  I think I have a mental block in this
area.  This is twice that I've asked about this sort of thing.  Thanks
for your patience.

$ jython
Jython 2.0 on javaVM-1.3.0.01 (JIT: null)
Type "copyright", "credits" or "license" for more information.
>>> tiffObj = open('john.tif', 'rb').read()
>>> open('junk.tif', 'wb').write(tiffObj)
>>> 
$ sum -r  junk.tif john.tif
16525    25 junk.tif
16525    25 john.tif
$ 

--- Finn Bock <bc...@wo...> wrote:
> [D-Man]
> 
> >On Thu, Mar 08, 2001 at 05:09:42PM -0800, John Mudd wrote:
> >| This should be easy.  Reading a binary file in Jython causes
> changes to
> >| the data?  But it works in Python.
> >
> >You forgot to mention that you are using a kernel/OS that likes to
> >mangle your data.  ;-)
> 
> I strongly suspect that John is using a *nix for the Jython test.
> 
> >Use _binary_ mode for writing _binary_ data.
> 
> Correct.
> 
> >| $ jython
> >| Jython 2.0 on javaVM-1.3.0.01 (JIT: null)
> >| Type "copyright", "credits" or "license" for more information.
> >| >>> tiffObj = open('john.tif', 'r').read()
> >| >>> open('junk.tif', 'w').write(tiffObj)
> >                        ^
> >This is "text" mode and Windoze likes to replace every \n with \r\n
> in
> >such streams.  This is what causes your data corruption. 
> Fortunately
> >on *nix systems the kernel doesn't mangle your streams under the
> hood.
> 
> Incorrect. It is Jython that does this mangling. The issue basicly
> is:
> should a read from a file into a unicode String read the data as
> binary
> (and always set the top 8 bit to zero) or as text by passing the data
> through the default encoding.
> 
> Without the 'b' flag, Jython is reading and writing the data as if
> using
> a Reader/Writer class. When you use the 'b' flag it uses a
> InputStream/OutputStream. 
> 
> This overloading of the 'b' flag (the flag also controls the platform
> dependent newline translation) is not a good thing, but it was the
> best
> I could come up with. Normally is works as expected and I think that
> also goes for John's case.
> 
> regards,
> finn
> 
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