Converting Byte to String and Back Properly in Python3?
Question:
Given a random byte (i.e. not only numbers/characters!), I need to convert it to a string and then back to the inital byte without loosing information. This seems like a basic task, but I ran in to the following problems:
Assuming:
rnd_bytes = b'wx12x96xb8'
len(rnd_bytes)
prints: 4
Now, converting it to a string. Note: I need to set backslashreplace as it otherwise returns a ‘UnicodeDecodeError’ or would loose information setting it to another flag value.
my_str = rnd_bytes.decode('utf-8' , 'backslashreplace')
Now, I have the string.
I want to convert it back to exactly the original byte (size 4!):
According to python ressources and this answer, there are different possibilities:
conv_bytes = bytes(my_str, 'utf-8')
conv_bytes = my_str.encode('utf-8')
But len(conv_bytes) returns 10.
I tried to analyse the outcome:
>>> repr(rnd_bytes)
"b'w\x12\x96\xb8'"
>>> repr(my_str)
"'w\x12\\x96\\xb8'"
>>> repr(conv_bytes)
"b'w\x12\\x96\\xb8'"
It would make sense to replace '\\'. my_str.replace('\\','\') doesn’t change anything. Probably, because four backslashes represent only two. So, my_str.replace('\','') would find the '\\', but leads to
SyntaxError: EOL while scanning string literal
due to the last argument ''. This had been discussed here, where the following suggestion came up:
>>> my_str2=my_str.encode('utf_8').decode('unicode_escape')
>>> repr(my_str2)
"'w\x12\x96¸'"
This replaces the '\\' but seems to add / change some other characters:
>>> conv_bytes2 = my_str2.encode('utf8')
>>> len(conv_bytes2)
6
>>> repr(conv_bytes2)
"b'w\x12\xc2\x96\xc2\xb8'"
There must be a prober way to convert a (complex) byte to a string and back. How can I achieve that?
Answers:
Note: Some codes found on the Internet.
You could try to convert it to hex format. Then it is easy to convert it back to byte format.
Sample code to convert bytes to string:
hex_str = rnd_bytes.hex()
Here is how ‘hex_str’ looks like:
'771296b8'
And code for converting it back to bytes:
new_rnd_bytes = bytes.fromhex(hex_str)
The result is:
b'wx12x96xb8'
For processing you can use:
readable_str = ''.join(chr(int(hex_str[i:i+2], 16)) for i in range(0, len(hex_str), 2))
But newer try to encode readable string, here is how readable string looks like:
'wx12x96¸'
After processing readable string convert it back to hex format before converting it back to bytes string like:
hex_str = ''.join([str(hex(ord(i)))[2:4] for i in readable_str])
Now, converting it to a string. Note: I need to set backslashreplace as it otherwise returns a ‘UnicodeDecodeError’ or would loose information setting it to another flag value.
The UTF-8 encoding cannot interpret every possible sequence of bytes as a string. Using backslashreplace gives you a string that preserves the information for bytes that couldn’t be converted:
>>> rnd_bytes = b'wx12x96xb8'
>>> rnd_bytes.decode('utf-8', 'backslashreplace')
'wx12\x96\xb8'
but that representation is not very useful for converting back.
Instead, use an encoding that does interpret every possible sequence of bytes as a string. The most straightforward of these is ISO-8859-1, which simply maps each byte one at a time to the first 256 Unicode code points respectively.
>>> rnd_bytes.decode('iso-8859-1')
'wx12x96¸'
>>> rnd_bytes.decode('iso-8859-1').encode('iso-8859-1') == rnd_bytes
True
Given a random byte (i.e. not only numbers/characters!), I need to convert it to a string and then back to the inital byte without loosing information. This seems like a basic task, but I ran in to the following problems:
Assuming:
rnd_bytes = b'wx12x96xb8'
len(rnd_bytes)
prints: 4
Now, converting it to a string. Note: I need to set backslashreplace as it otherwise returns a ‘UnicodeDecodeError’ or would loose information setting it to another flag value.
my_str = rnd_bytes.decode('utf-8' , 'backslashreplace')
Now, I have the string.
I want to convert it back to exactly the original byte (size 4!):
According to python ressources and this answer, there are different possibilities:
conv_bytes = bytes(my_str, 'utf-8')
conv_bytes = my_str.encode('utf-8')
But len(conv_bytes) returns 10.
I tried to analyse the outcome:
>>> repr(rnd_bytes)
"b'w\x12\x96\xb8'"
>>> repr(my_str)
"'w\x12\\x96\\xb8'"
>>> repr(conv_bytes)
"b'w\x12\\x96\\xb8'"
It would make sense to replace '\\'. my_str.replace('\\','\') doesn’t change anything. Probably, because four backslashes represent only two. So, my_str.replace('\','') would find the '\\', but leads to
SyntaxError: EOL while scanning string literal
due to the last argument ''. This had been discussed here, where the following suggestion came up:
>>> my_str2=my_str.encode('utf_8').decode('unicode_escape')
>>> repr(my_str2)
"'w\x12\x96¸'"
This replaces the '\\' but seems to add / change some other characters:
>>> conv_bytes2 = my_str2.encode('utf8')
>>> len(conv_bytes2)
6
>>> repr(conv_bytes2)
"b'w\x12\xc2\x96\xc2\xb8'"
There must be a prober way to convert a (complex) byte to a string and back. How can I achieve that?
Note: Some codes found on the Internet.
You could try to convert it to hex format. Then it is easy to convert it back to byte format.
Sample code to convert bytes to string:
hex_str = rnd_bytes.hex()
Here is how ‘hex_str’ looks like:
'771296b8'
And code for converting it back to bytes:
new_rnd_bytes = bytes.fromhex(hex_str)
The result is:
b'wx12x96xb8'
For processing you can use:
readable_str = ''.join(chr(int(hex_str[i:i+2], 16)) for i in range(0, len(hex_str), 2))
But newer try to encode readable string, here is how readable string looks like:
'wx12x96¸'
After processing readable string convert it back to hex format before converting it back to bytes string like:
hex_str = ''.join([str(hex(ord(i)))[2:4] for i in readable_str])
Now, converting it to a string. Note: I need to set backslashreplace as it otherwise returns a ‘UnicodeDecodeError’ or would loose information setting it to another flag value.
The UTF-8 encoding cannot interpret every possible sequence of bytes as a string. Using backslashreplace gives you a string that preserves the information for bytes that couldn’t be converted:
>>> rnd_bytes = b'wx12x96xb8'
>>> rnd_bytes.decode('utf-8', 'backslashreplace')
'wx12\x96\xb8'
but that representation is not very useful for converting back.
Instead, use an encoding that does interpret every possible sequence of bytes as a string. The most straightforward of these is ISO-8859-1, which simply maps each byte one at a time to the first 256 Unicode code points respectively.
>>> rnd_bytes.decode('iso-8859-1')
'wx12x96¸'
>>> rnd_bytes.decode('iso-8859-1').encode('iso-8859-1') == rnd_bytes
True