Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Programming > Python > Re: write binary with struct.pack_into

Reply
Thread Tools

Re: write binary with struct.pack_into

 
 
Peter Otten
Guest
Posts: n/a
 
      10-06-2012
palmeira wrote:

> Dear pythonists,
>
> I'm having a problem with read/write binary in python.
> I have a binary file that I need to read information, extract a array,
> modify this array and put these values into file again in same binary
> format.
> I need to use unpack_from and pack_into because sometimes gonna need
> read/write in the middle of file.


Use pack/unpack and file.seek() instead.

> Script:
>
> import struct
> bloco='>%df' %(252) #Binary format
>
> # READ
> fa=open('testIN.bin')
> my_array=struct.unpack_from(bloco,fa.read()[0*4:251*4]) # my_aray = 252
> elements array
> ## This read is OK!
>
> #WRITE
> fb=open('testOUT.bin')
> test=struct.pack_into(bloco,fb.write()[0*4:251*4]) # ERROR in this WRITE


However, I think you have picked the wrong API. So:

# untested

import sys
import array

offset = 0
N = 252

a = array.array("f")
with open("testIN.bin", "rb") as f:
f.seek(offset)
a.read(f, N)
if sys.byteorder == "little":
a.byteswap()

# process a

if sys.byteorder == "little":
a.byteswap()
with open("testOUT.bin", "wb") as f:
f.seek(offset)
a.write(f)


 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
x86 binary runs; x86_64 binary throws segfault Don C Programming 60 03-19-2010 05:58 AM
(8-bit binary to two digit bcd) or (8-bit binary to two digit seven segment) Fangs VHDL 3 10-26-2008 06:41 AM
writing binary file (ios::binary) Ron Eggler C++ 9 04-28-2008 08:20 AM
A 64-bit binary returning a value to a 32-bit binary? spammenotplui31@yahoo.ca C Programming 12 04-08-2007 07:02 AM
Re: ostreams, ios::binary, endian, mixed binary-ascii Marc Schellens C++ 8 07-15-2003 12:27 PM



Advertisments