Splitting a float into bytes:

2006-07-26 Thread Michael Yanowitz 
Hello:

  For some reason I can't figure out how to split
a 4-byte (for instance) float number (such as 3.14159265359)
into its 4-bytes so I can send it via a socket to another
computer.
  For integers, it is easy, I can get the 4 bytes by anding like:
byte1 = int_val  0x00FF
byte2 = int_val  0xFF00
byte3 = int_val  0x00FF
byte4 = int_val  0xFF00
  But if I try to do that with floats I get:
 pi  0xFF
Traceback (most recent call last):
  File stdin, line 1, in ?
TypeError: unsupported operand type(s) for : 'float' and 'int'

  Is there some easy way to get what the bytes of the float are?

Thanks in advance:
Michael Yanowitz


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Re: Splitting a float into bytes:

2006-07-26 Thread Simon Forman 
Michael Yanowitz wrote:
 Hello:

   For some reason I can't figure out how to split
 a 4-byte (for instance) float number (such as 3.14159265359)
 into its 4-bytes so I can send it via a socket to another
 computer.
   For integers, it is easy, I can get the 4 bytes by anding like:
 byte1 = int_val  0x00FF
 byte2 = int_val  0xFF00
 byte3 = int_val  0x00FF
 byte4 = int_val  0xFF00
   But if I try to do that with floats I get:
  pi  0xFF
 Traceback (most recent call last):
   File stdin, line 1, in ?
 TypeError: unsupported operand type(s) for : 'float' and 'int'

   Is there some easy way to get what the bytes of the float are?

 Thanks in advance:
 Michael Yanowitz

The struct module.  (It also works for ints. ;-)  )

http://docs.python.org/lib/module-struct.html


HTH,
~Simon

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RE: Splitting a float into bytes:

2006-07-26 Thread Michael Yanowitz 

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf
Of Simon Forman
Sent: Wednesday, July 26, 2006 2:56 PM
To: python-list@python.org
Subject: Re: Splitting a float into bytes:


Michael Yanowitz wrote:
 Hello:

   For some reason I can't figure out how to split
 a 4-byte (for instance) float number (such as 3.14159265359)
 into its 4-bytes so I can send it via a socket to another
 computer.
   For integers, it is easy, I can get the 4 bytes by anding like:
 byte1 = int_val  0x00FF
 byte2 = int_val  0xFF00
 byte3 = int_val  0x00FF
 byte4 = int_val  0xFF00
   But if I try to do that with floats I get:
  pi  0xFF
 Traceback (most recent call last):
   File stdin, line 1, in ?
 TypeError: unsupported operand type(s) for : 'float' and 'int'

   Is there some easy way to get what the bytes of the float are?

 Thanks in advance:
 Michael Yanowitz

The struct module.  (It also works for ints. ;-)  )

http://docs.python.org/lib/module-struct.html


HTH,
~Simon

   Thanks, but maybe I am missing something.
If I use pack, doesn't it have to be unpacked at the other end
to make sense? The data will be picked up on some other computer
by some other application probably written in C or C++. Would
it have to be rewritten to unpack the data?

Thanks in advance:
Michael Yanowitz 


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Re: Splitting a float into bytes:

2006-07-26 Thread spartacus 
Yes i think you can. If you use the struct module.

 import struct
 import math
y = struct.pack('!f', math.pi)
print repr(y)
'@I\x0f\xdb'


Michael Yanowitz [EMAIL PROTECTED] wrote in message 
news:[EMAIL PROTECTED]
 Hello:

  For some reason I can't figure out how to split
 a 4-byte (for instance) float number (such as 3.14159265359)
 into its 4-bytes so I can send it via a socket to another
 computer.
  For integers, it is easy, I can get the 4 bytes by anding like:
 byte1 = int_val  0x00FF
 byte2 = int_val  0xFF00
 byte3 = int_val  0x00FF
 byte4 = int_val  0xFF00
  But if I try to do that with floats I get:
 pi  0xFF
 Traceback (most recent call last):
  File stdin, line 1, in ?
 TypeError: unsupported operand type(s) for : 'float' and 'int'

  Is there some easy way to get what the bytes of the float are?

 Thanks in advance:
 Michael Yanowitz

 


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Re: Splitting a float into bytes:

2006-07-26 Thread Simon Forman 
Michael Yanowitz wrote:
 -Original Message-
 From: [EMAIL PROTECTED]
 [mailto:[EMAIL PROTECTED] Behalf
 Of Simon Forman
 Sent: Wednesday, July 26, 2006 2:56 PM
 To: python-list@python.org
 Subject: Re: Splitting a float into bytes:


 Michael Yanowitz wrote:
  Hello:
 
For some reason I can't figure out how to split
  a 4-byte (for instance) float number (such as 3.14159265359)
  into its 4-bytes so I can send it via a socket to another
  computer.
For integers, it is easy, I can get the 4 bytes by anding like:
  byte1 = int_val  0x00FF
  byte2 = int_val  0xFF00
  byte3 = int_val  0x00FF
  byte4 = int_val  0xFF00
But if I try to do that with floats I get:
   pi  0xFF
  Traceback (most recent call last):
File stdin, line 1, in ?
  TypeError: unsupported operand type(s) for : 'float' and 'int'
 
Is there some easy way to get what the bytes of the float are?
 
  Thanks in advance:
  Michael Yanowitz

 The struct module.  (It also works for ints. ;-)  )

 http://docs.python.org/lib/module-struct.html


 HTH,
 ~Simon

Thanks, but maybe I am missing something.
 If I use pack, doesn't it have to be unpacked at the other end
 to make sense? The data will be picked up on some other computer
 by some other application probably written in C or C++. Would
 it have to be rewritten to unpack the data?

 Thanks in advance:
 Michael Yanowitz

It says in the docs This module performs conversions between Python
values and C structs represented as Python strings.  This means, to
me, that the packed data will be in the format that C (and C++ I would
assume) uses.

You might have to mind the endian-ness if you're transferring data
between different architectures, but struct includes format specifiers
for this.

Have fun,
~Simon

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Re: Splitting a float into bytes:

2006-07-26 Thread John Machin 

Michael Yanowitz wrote:
 Hello:

   For some reason I can't figure out how to split
 a 4-byte (for instance) float number (such as 3.14159265359)
 into its 4-bytes so I can send it via a socket to another
 computer.
   For integers, it is easy, I can get the 4 bytes by anding like:
 byte1 = int_val  0x00FF
 byte2 = int_val  0xFF00
 byte3 = int_val  0x00FF
 byte4 = int_val  0xFF00

Errrmmm ... I think you need the right shift operator e.g.
 byte4 = (int_val  0xFF00)  24
but assert 0 = byte4 = 255 may fail under some circumstances
so (better):
 byte4 = (int_val  24)  0xFF
# absolutely guaranteed to pass that assertion

BUT why muck around with all that when you can use struct.pack???

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