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file.read problem

 
 
wscrsurfdude
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      02-17-2006
f = open('myfile,'r')
a = f.read(5000)

When I do this I get the first 634 bytes. I tried using the:
f = open('myfile,'rb')
option, but now there are a few 0x0D bytes extra in myfile. 0x0D =
Carriage return. How can I make a program that not puts in the 0x0D
bytes in windows.

In linux the first 2 lines are working perfectly.

 
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Farshid Lashkari
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      02-17-2006
> When I do this I get the first 634 bytes. I tried using the:
> f = open('myfile,'rb')
> option, but now there are a few 0x0D bytes extra in myfile. 0x0D =
> Carriage return. How can I make a program that not puts in the 0x0D
> bytes in windows.



Try opening the file in 'rbU' mode. This will use universal newline mode
and convert all carriage returns to line feeds.

-Farshid
 
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wscrsurfdude
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      02-17-2006
>Try opening the file in 'rbU' mode. This will use universal newline mode
>and convert all carriage returns to line feeds.


I tried this, but as you say, now there are 0x0A bytes extra in my
files, is there also a possibility to let all these things out, and
just get the file.

I am working on a script to get parts of raw data out of a file, and
the data I read has to be the data written in the file without CR or
LF.

 
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Farshid Lashkari
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      02-17-2006
> I am working on a script to get parts of raw data out of a file, and
> the data I read has to be the data written in the file without CR or
> LF.


So you just want to remove all the linefeeds? This should work then:

data = data.replace('\n','')

-Farshid

 
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wscrsurfdude
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      02-17-2006

Farshid Lashkari wrote:
> > I am working on a script to get parts of raw data out of a file, and
> > the data I read has to be the data written in the file without CR or
> > LF.

>
> So you just want to remove all the linefeeds? This should work then:
>
> data = data.replace('\n','')
>
> -Farshid


The problem is if I remove the linefeeds, I also delete readout data if
it is 0x0A, and I don't want this, because the files I readout has to
be a part of the original data. Another idea??

But still my question is why is the:
f = open('myfile,'r')
a = f.read(5000)
working in linux??

 
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Fredrik Lundh
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      02-17-2006
"wscrsurfdude" wrote:

> >Try opening the file in 'rbU' mode. This will use universal newline mode
> >and convert all carriage returns to line feeds.

>
> I tried this, but as you say, now there are 0x0A bytes extra in my
> files, is there also a possibility to let all these things out, and
> just get the file.
>
> I am working on a script to get parts of raw data out of a file, and
> the data I read has to be the data written in the file without CR or
> LF.


what kind of file are you reading? if it's a text file, it's supposed to have
LF in it (or CR LF if you read it in binary mode); the LF:s are there to tell
you where each line ends.

if it's a binary file, open with mode "rb".

</F>



 
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wscrsurfdude
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      02-17-2006
>if it's a binary file, open with mode "rb".
You are right about opening it in the rb mode (flaw in the start post),
but also when I do this in windows in front of every 0x0A is put a
0x0D. I found a explanation why it is working in linux it is below in
my post.

But what i get of this that in windows in front of every 0x0A is put a
0x0D as a line feed. II have to get rid of these. But if there is
already binary data in my original file with the data 0x0D0A the 0x0D
also is deleted, someone has an idea??

############################################
The whole subject of newlines and text files is a murky area of non
standard implementation by different operating systems. These
differences have their roots in the early days of data communications
and the control of mechanical teleprinters. Basically there are 3
different ways to indicate a new line:

Carriage Return (CR) character ('\r')
Line Feed (LF) character ('\n')
CR/LF pair ('\r\n').
All three techniques are used in different operating systems. MS DOS
(and therefore Windows) uses method 3. Unix (including Linux) uses
method 2. Apple in its original MacOS used method 1, but now uses
method 2 since MacOS X is really a variant of Unix.

So how can the poor programmer cope with this multiplicity of line
endings? In many languages she just has to do lots of tests and take
different action per OS. In more modern languages, including Python,
the language provides facilities for dealing with the mess for you. In
the case of Python the assistance comes in the form of the os module
which defines a variable called linesep which is set to whatever the
newline character is on the current operating system. This makes adding
newlines easy, and rstrip() takes account of the OS when it does its
work of removing them, so really the simple way to stay sane, so far as
newlines are concerned is: always use rstrip() to remove newlines from
lines read from a file and always add os.linesep to strings being
written to a file.

That still leaves the awkward situation where a file is created on one
OS and then processed on another, incompatible, OS and sadly, there
isn't much we can do about that except to compare the end of the line
with os.linesep to determine what the difference is.
######################################

 
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wscrsurfdude
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      02-17-2006
I have the solution, the flaw was not in the opening of the file, but
in the writing of the file. Stupid me, i opened it with mode rb, but
wrote it with w instead of with wb

Everybody thanks for helping me.

 
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Steven D'Aprano
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      02-17-2006
On Fri, 17 Feb 2006 00:15:31 -0800, wscrsurfdude wrote:

>
> Farshid Lashkari wrote:
>> > I am working on a script to get parts of raw data out of a file, and
>> > the data I read has to be the data written in the file without CR or
>> > LF.

>>
>> So you just want to remove all the linefeeds? This should work then:
>>
>> data = data.replace('\n','')
>>
>> -Farshid

>
> The problem is if I remove the linefeeds, I also delete readout data if
> it is 0x0A, and I don't want this, because the files I readout has to
> be a part of the original data. Another idea??


Er, have I understood you correctly? You seem to be saying that some
linefeeds are significant data, and some are not, and you want somebody to
tell you how to remove the insignificant "linefeed = end of line"
characters without removing the significant "linefeed = important data"
characters.

That's easy:

from blackmagic import readmymind, dowhatiwant
fp = file("data", "rb")
readmymind()
data = dowhatiwant(fp.read())

You'll need Python 3.0 for the blackmagic module.

*wink*

Seriously, if this is your problem, then you will have no choice but to
carefully analyse the file yourself, looking at each linefeed and tossing
it away if it is insignificant. We can't tell you how to do that, because
we don't know which linefeeds are data and which are not.



> But still my question is why is the:
> f = open('myfile,'r')
> a = f.read(5000)
> working in linux??


Why shouldn't it work in Linux? The question should be, why is it not
working in Windows? (When did "my code is broken" become the excepted
state of affairs, and "my code works" the mystery that needs solving?)

I wonder whether there is a ctrl-Z in your data, and Windows is
interpreting that as end of file.


--
Steven.

 
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Fredrik Lundh
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      02-17-2006
"wscrsurfdude" wrote:

> >if it's a binary file, open with mode "rb".


> You are right about opening it in the rb mode (flaw in the start post),
> but also when I do this in windows in front of every 0x0A is put a
> 0x0D. I found a explanation why it is working in linux it is below in
> my post.
>
> But what i get of this that in windows in front of every 0x0A is put a
> 0x0D as a line feed. II have to get rid of these.


if you open a file in binary mode ("rb"), you get the data that's in the
file. no more, no less. if someone's adding CR to the files, that happens
before you opened them in Python.

have you, perhaps, copied binary files between the systems using FTP
in text mode? if so, you've damaged the files, and there's no way to fix
them, in general.

</F>



 
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