Adding values to binary string

Question

I would like to add hexvalues to a binary string so that I end up with a binary string that can be transmitted. What I want is: StringToAppend = "5ce7e615ff0000000000010202041f0140009e005d006404084c5ce82215ff1d02000000010202041f013b0097005c005e04777c" (I have this in unhexlified form and want to append it to a string a la StatusStr = chr(0) How do I do this??? This is what i have:

>>> not_macs_buffer=     unhexlify("5ce7e615ff0000000000010202041f0140009e005d006404084c5ce82215ff1d02000000010202041    f013b0097005c005e04777c")
>>> StatusStr = chr(0)
>>> for i in xrange(0,len(not_macs_buffer)):
...     StatusStr +=chr(not_macs_buffer[i])
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
TypeError: an integer is required
>>>

It isn't very clear here what you want to do. Perhaps a smaller example with a step by step bit of code would work better... — PearsonArtPhoto
– PearsonArtPhoto, Commented Nov 14, 2012 at 1:47
are you sure that's your example code? I get: TypeError: Non-hexadecimal digit found when I try to run binascii.unhexlify -- Probably due to the whitespace in there ... — mgilson
– mgilson, Commented Nov 14, 2012 at 1:48
Also, am I missing here or do you just want StatusStr = chr(0) + unhexlify(...)? — mgilson
– mgilson, Commented Nov 14, 2012 at 1:49
mgilson - no, i need to string in binary form i.e. "unhexlified" — stdcerr
– stdcerr, Commented Nov 14, 2012 at 15:25

Laurence Dougal Myers · Accepted Answer · 2012-11-14 02:30:33Z

1

What are you transmitting the string to/from? Does it have to be in hex?

The issue seems to be that are you are converting your hex string into a binary string, then in your loop you are attempting to convert a string character into a character, using chr(). This fails because chr() only takes an integer value representing a 256-value ASCII code, not a string.

To fix your problem, just change StatusStr +=chr(not_macs_buffer[i]) to this:

StatusStr += not_macs_buffer[i]

Of course, you could forgo the loop completely.

StatusStr = chr(0) + not_macs_buffer

And if you really did need to convert a list of integers to a string, you could use a list comprehension and then join the list. (I won't give an example since it's not relevant)

EDIT:

If you want to add the null value to your original hex string, you can do this:

StringToAppend = '5ce7e6' # ... snip the real value
StatusStr = hexlify(chr(0)) + StringToAppend 
# or
StatusStr = hexlify('\x00') + StringToAppend 
# or
StatusStr = '0000' + StringToAppend

edited Nov 14, 2012 at 2:30

answered Nov 14, 2012 at 1:49

Laurence Dougal Myers

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2 Comments

stdcerr Over a year ago

No, I actually want to compile a binary strong like: "000b13AB" = list of values like 0x00 0x0b 0x13 0xab

Laurence Dougal Myers Over a year ago

I think you need to be clear on your terminology. Python stores binary values in a string using escape characters, like so: "\x00\x0B\x13\xAB". What you have listed is a string containing hexadecimal characters, "000B13AB". Hexlify will convert the binary string to hexadecimal characters, unhexlify will convert the hexadecimal characters to a binary string. If you want to add a value to the binary string, just do '\x00' + unhexlify(StringToAppend).

stdcerr · Accepted Answer · 2012-11-15 04:39:30Z

0

Well, Thanks all but what I actually ended up doing to get what I wanted, is:

>>> not_macs_buffer=         unhexlify("5ce7e615ff0000000000010202041f0140009e005d006404084c5ce82215ff1d02000000010202041      f013b0097005c005e04777c")
>>> StatusStr = chr(0)
>>> for i in xrange(0,len(not_macs_buffer)):
...     StatusStr +=chr(ord(not_macs_buffer[i]))

answered Nov 15, 2012 at 4:39

stdcerr

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2 Comments

Laurence Dougal Myers Over a year ago

Just so you know, "chr(ord(not_macs_buffer[i]))" can be replaced with just "not_macs_buffer[i]". You're converting a character in a string to an integer and back to a string, which is redundant.

stdcerr Over a year ago

no, that what confused me as well, it gives me an "an integer is required" - error - must be something with unicode or utf-8 or so I assumed...?

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