Develop Reference

How do I convert hex to utf-8?

I want to convert a hex string to utf-8
a = '0xb3d9'
to
동 (http://www.unicodemap.org/details/0xB3D9/index.html)

First, obtain the integer value from the string of a, noting that a is expressed in hexadecimal:
a_int = int(a, 16)
Next, convert this int to a character. In python 2 you need to use the unichr method to do this, because the chr method can only deal with ASCII characters:
a_chr = unichr(a_int)
Whereas in python 3 you can just use the chr method for any character:
a_chr = chr(a_int)
So, in python 3, the full command is:
a_chr = chr(int(a, 16))

How can I concatenate string to a string as a hex in python?

data = "\xAA\x12\xFF\x01\x21\x33"
ser.write(data)
This is the original code. How can I concatenate a string to a string (which contains hexa numbers) and use the all as a hexa number to send it as a hexa oder like the second code?
var = 21
data = "\xAA\x12\xFF\x01" + var + "\x33"
ser.write(data)

What you're looking for is hex() function:
>>> var = 21
>>> data = "\xAA\x12\xFF\x01" + hex(var) + "\x33"
>>> data
'\xaa\x12\xff\x01\0x153'
>>>
hex() job is to convert an integer number (of any size) to a lowercase hexadecimal string prefixed with “0x”.
EDIT:
I noticed you need the backslash to keep the formatting, so chr() will return the hexa value with the backslash.
>>> chr(var)
'\x15'
>>> hex(var)
'0x15'
chr(i) returns a string of one character whose ASCII code is the integer i.

How to remove '\x' from a hex string in Python?

I'm reading a wav audio file in Python using wave module. The readframe() function in this library returns frames as hex string. I want to remove \x of this string, but translate() function doesn't work as I want:
>>> input = wave.open(r"G:\Workspace\wav\1.wav",'r')
>>> input.readframes (1)
'\xff\x1f\x00\xe8'
>>> '\xff\x1f\x00\xe8'.translate(None,'\\x')
'\xff\x1f\x00\xe8'
>>> '\xff\x1f\x00\xe8'.translate(None,'\x')
ValueError: invalid \x escape
>>> '\xff\x1f\x00\xe8'.translate(None,r'\x')
'\xff\x1f\x00\xe8'
>>>
Any way I want divide the result values by 2 and then add \x again and generate a new wav file containing these new values. Does any one have any better idea?
What's wrong?

Indeed, you don't have backslashes in your string. So, that's why you can't remove them.
If you try to play with each hex character from this string (using ord() and len() functions - you'll see their real values. Besides, the length of your string is just 4, not 16.
You can play with several solutions to achieve your result:
'hex' encode:
'\xff\x1f\x00\xe8'.encode('hex')
'ff1f00e8'
Or use repr() function:
repr('\xff\x1f\x00\xe8').translate(None,r'\\x')

One way to do what you want is:
>>> s = '\xff\x1f\x00\xe8'
>>> ''.join('%02x' % ord(c) for c in s)
'ff1f00e8'
The reason why translate is not working is that what you are seeing is not the string itself, but its representation. In other words, \x is not contained in the string:
>>> '\\x' in '\xff\x1f\x00\xe8'
False
\xff, \x1f, \x00 and \xe8 are the hexadecimal representation of for characters (in fact, len(s) == 4, not 24).

Use the encode method:
>>> s = '\xff\x1f\x00\xe8'
>>> print s.encode("hex")
'ff1f00e8'

As this is a hexadecimal representation, encode with hex
>>> '\xff\x1f\x00\xe8'.encode('hex')
'ff1f00e8'

as I hold the string of hexadecimal format without encoding the string?

The general problem is that I need the hexadecimal string stays in that format to assign it to a variable and not to save the coding?
no good:
>>> '\x61\x74'
'at'
>>> a = '\x61\x74'
>>> a
'at'
works well, but is not as:
>>> '\x61\x74'
'\x61\x74' ????????
>>> a = '\x61\x74'
>>> a
'\x61\x74' ????????

Use r prefix (explained on SO)
a = r'\x61\x74'
b = '\x61\x74'
print (a) #prints \x61\x74
print (b) # prints at

It is the same data. Python lets you specify a literal string using different methods, one of which is to use escape codes to represent bytes.
As such, '\x61' is the same character value as 'a'. Python just chooses to show printable ASCII characters as printable ASCII characters instead of the escape code, just because that makes working with bytestrings that much easier.
If you need the literal slash, x character and the two digit 6 and 1 characters (so a string of length 4), you need to double the slash or use raw strings.
To illustrate:
>>> '\x61' == 'a' # two notations for the same value
True
>>> len('\x61') # it's just 1 character
1
>>> '\\x61' # escape the escape
'\\x61'
>>> r'\x61' # or use a raw literal instead
'\\x61'
>>> len('\\x61') # which produces 4 characters
4

Convert hex-string to string using binascii

By hex-string, it is a regular string except every two characters represents some byte, which is mapped to some ASCII char.
So for example the string
abc
Would be represented as
979899
I am looking at the binascii module but don't really know how to take the hex-string and turn it back into the ascii string.
Which method can I use?
Note: I am starting with 979899 and want to convert it back to abc

You can use ord() to get the integer value of each character:
>>> map(ord, 'abc')
[97, 98, 99]
>>> ''.join(map(lambda c: str(ord(c)), 'asd'))
'979899'
>>> ''.join((str(ord(c)) for c in 'abc'))
'979899'

You don't need binascii to get the integer representation of a character in a string, all you need is the built in function ord().
s = 'abc'
print(''.join(map(lambda x:str(ord(x)),s))) # outputs "979899"

To get the string back from the hexadecimal number you can use
s=str(616263)
print "".join([chr(int(s[x:x+2], 16)) for x in range(0,len(s),2)])
See http://ideone.com/dupgs