[newbie] Saving binaries in a specific way

[Tim Chase]

On 2013-12-16 14:19, Djoser wrote:
> I am new to this forum and also to Python, but I'm trying hard to
> understand it  better.

Welcome aboard!

> I need to create a binary file, but the first 4 lines must be in
> signed-Integer16 and all the others in signed-Integer32. I have a
> program that does that with Matlab and other with Mathematica, but
> I'm converting all for Python.

You seem to be conflating ideas here:  a binary file doesn't really
have "lines".  Do you mean "first 4 bytes"?  If so, then a
signed-Integer16 really only occupies 2 bytes, so you'd have to pad
it somehow.  That said, I suspect that the "struct" module will get
you what you want:

  from struct import pack
  header16bit = 31415
  data = list(range(10))
  with open('output.bin', 'wb') as f:
    f.write(pack('h', header16bit))
    for signed_32bit_number in data:
      f.write(pack('i', signed_32bit_number))
    f.write(other_stuff)

You might need to specify the byte-ordering, which you can do by
prefixing the "h" or "i" with ">", "<" or "=" s documented at [1]

-tkc

[1]
http://www.python.org/doc//current/library/struct.html





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