I am using webpage to get data in hex to write serial modbus using python
Issue is that 0A in the string gets converted to \n.
How to stop this from happening?
rList = r'0106000600000AE9CC'
arr=str(rList)
arr = bytes.fromhex(rList)
print(arr)
Output:
b'\x01\x06\x00\x06\x00\x00\n\xe9\xcc'
The repr() representation of a bytes object uses ASCII code points wherever possible.
What this means is \x0A will be displayed as \n, because that's the ASCII code point for a newline.
More examples:
\x55 will be displayed as U, \x5A will be displayed as Z, \x0D will be displayed as \r, you get the idea.
However, the data under the hood is still the same.
Don't worry about how the output string is displayed by the Python console—it's presumably more important to process its content.
Try this
def print_me(thing: bytes):
print(''.join(
f'\\x{byte:02x}'
for byte in thing
))
print_me(bytes.fromhex("0106000600000AE9CC"))
Output:
\x01\x06\x00\x06\x00\x00\x0a\xe9\xcc
b symbol before string means you have a list of bytes. As you print it, python tries to decode bytes whenever possible to represent them in symbols for simplicity.
Byte b'\x0A' corresponds to decimal value 10, which is a newline symbol in ascii. That is why you get this symbol printed.
Under the hood your byte b'\x0A' has not been changed.
I'm trying to convert a binary I have in python (a gzipped protocol buffer object) to an hexadecimal string in a string escape fashion (eg. \xFA\x1C ..).
I have tried both
repr(<mygzipfileobj>.getvalue())
as well as
<mygzipfileobj>.getvalue().encode('string-escape')
In both cases I end up with a string which is not made of HEX chars only.
\x86\xe3$T]\x0fPE\x1c\xaa\x1c8d\xb7\x9e\x127\xcd\x1a.\x88v ...
How can I achieve a consistent hexadecimal conversion where every single byte is actually translated to a \xHH format ? (where H represents a valid hex char 0-9A-F)
The \xhh format you often see is a debugging aid, the output of the repr() applied to a string with non-ASCII codepoints. Any ASCII codepoints are left a in-place to leave what readable information is there.
If you must have a string with all characters replaced by \xhh escapes, you need to do so manually:
''.join(r'\x{0:02x}'.format(ord(c)) for c in value)
If you need quotes around that, you'd need to add those manually too:
"'{0}'".format(''.join(r'\x{:02x}'.format(ord(c)) for c in value))
I have everything working as I want it in my code, but I'm still curious. I have a string: "stación." When I convert that string to unicode, I get:
unicode('stación', 'utf-8')
>>> u'staci\xf3n'
That "\xf3" in there looks like a byte character. This is different from:
unicode('Поиск', 'utf-8')
>>> u'\u041f\u043e\u0438\u0441\u043a'
In the latter example, as with everything I've converted to unicode before, I get unicode characters starting with "\u." Normally, when I see a byte starting with "\x," I think there's a problem. What gives here? Is this because "ó" is extended ASCII?
No, it's because "ó" is a non-ASCII character within the first 255 characters. Since it's representable using a single byte, we save 2 characters in the representation. The other two representations are valid, but not required.
>>> u'\u00f3'
u'\xf3'
>>> u'\U000000f3'
u'\xf3'
u'\xf3' is not a byte; it is a Unicode string with a single Unicode codepoint (U+00f3 LATIN SMALL LETTER O WITH ACUTE).
What you see (u'\xf3') is how Python 2 chooses to represent Unicode character with Unicode ordinals (integers) in the range 0..255 that are not printable ascii characters (Python 3 would show 'ó' here, only non-printable characters use '\xhh' form there by default). As #Ignacio Vazquez-Abrams said: u'\u00f3' and u'\U000000f3' literals create exactly the same Unicode string.
You could see how the Unicode character (u'\xf3') looks like bytes in different character encodings for comparision:
>>> print(u'\xf3')
ó
>>> u'\xf3'.encode('utf-8')
b'\xc3\xb3'
>>> u'\xf3'.encode('utf-16be')
b'\x00\xf3'
>>> u'\xf3'.encode('utf-32le')
b'\xf3\x00\x00\x00'
>>> u'\xf3'.encode('cp1252')
b'\xf3'
Note: b'\xf3' and u'\xf3' are different things. The former is a bytestring that contains a single byte (an integer 243), the latter is a Unicode string that contains a single Unicode codepoint (Unicode ordinal 243). The number is the same 243 by the units are different -- 100 calories is not the same thing as 100 grams.
Working with Python 2.7, I'm wondering what real advantage there is in using the type unicode instead of str, as both of them seem to be able to hold Unicode strings. Is there any special reason apart from being able to set Unicode codes in unicode strings using the escape char \?:
Executing a module with:
# -*- coding: utf-8 -*-
a = 'á'
ua = u'á'
print a, ua
Results in: á, á
More testing using Python shell:
>>> a = 'á'
>>> a
'\xc3\xa1'
>>> ua = u'á'
>>> ua
u'\xe1'
>>> ua.encode('utf8')
'\xc3\xa1'
>>> ua.encode('latin1')
'\xe1'
>>> ua
u'\xe1'
So, the unicode string seems to be encoded using latin1 instead of utf-8 and the raw string is encoded using utf-8? I'm even more confused now! :S
unicode is meant to handle text. Text is a sequence of code points which may be bigger than a single byte. Text can be encoded in a specific encoding to represent the text as raw bytes(e.g. utf-8, latin-1...).
Note that unicode is not encoded! The internal representation used by python is an implementation detail, and you shouldn't care about it as long as it is able to represent the code points you want.
On the contrary str in Python 2 is a plain sequence of bytes. It does not represent text!
You can think of unicode as a general representation of some text, which can be encoded in many different ways into a sequence of binary data represented via str.
Note: In Python 3, unicode was renamed to str and there is a new bytes type for a plain sequence of bytes.
Some differences that you can see:
>>> len(u'à') # a single code point
1
>>> len('à') # by default utf-8 -> takes two bytes
2
>>> len(u'à'.encode('utf-8'))
2
>>> len(u'à'.encode('latin1')) # in latin1 it takes one byte
1
>>> print u'à'.encode('utf-8') # terminal encoding is utf-8
à
>>> print u'à'.encode('latin1') # it cannot understand the latin1 byte
�
Note that using str you have a lower-level control on the single bytes of a specific encoding representation, while using unicode you can only control at the code-point level. For example you can do:
>>> 'àèìòù'
'\xc3\xa0\xc3\xa8\xc3\xac\xc3\xb2\xc3\xb9'
>>> print 'àèìòù'.replace('\xa8', '')
à�ìòù
What before was valid UTF-8, isn't anymore. Using a unicode string you cannot operate in such a way that the resulting string isn't valid unicode text.
You can remove a code point, replace a code point with a different code point etc. but you cannot mess with the internal representation.
Unicode and encodings are completely different, unrelated things.
Unicode
Assigns a numeric ID to each character:
0x41 → A
0xE1 → á
0x414 → Д
So, Unicode assigns the number 0x41 to A, 0xE1 to á, and 0x414 to Д.
Even the little arrow → I used has its Unicode number, it's 0x2192. And even emojis have their Unicode numbers, 😂 is 0x1F602.
You can look up the Unicode numbers of all characters in this table. In particular, you can find the first three characters above here, the arrow here, and the emoji here.
These numbers assigned to all characters by Unicode are called code points.
The purpose of all this is to provide a means to unambiguously refer to a each character. For example, if I'm talking about 😂, instead of saying "you know, this laughing emoji with tears", I can just say, Unicode code point 0x1F602. Easier, right?
Note that Unicode code points are usually formatted with a leading U+, then the hexadecimal numeric value padded to at least 4 digits. So, the above examples would be U+0041, U+00E1, U+0414, U+2192, U+1F602.
Unicode code points range from U+0000 to U+10FFFF. That is 1,114,112 numbers. 2048 of these numbers are used for surrogates, thus, there remain 1,112,064. This means, Unicode can assign a unique ID (code point) to 1,112,064 distinct characters. Not all of these code points are assigned to a character yet, and Unicode is extended continuously (for example, when new emojis are introduced).
The important thing to remember is that all Unicode does is to assign a numerical ID, called code point, to each character for easy and unambiguous reference.
Encodings
Map characters to bit patterns.
These bit patterns are used to represent the characters in computer memory or on disk.
There are many different encodings that cover different subsets of characters. In the English-speaking world, the most common encodings are the following:
ASCII
Maps 128 characters (code points U+0000 to U+007F) to bit patterns of length 7.
Example:
a → 1100001 (0x61)
You can see all the mappings in this table.
ISO 8859-1 (aka Latin-1)
Maps 191 characters (code points U+0020 to U+007E and U+00A0 to U+00FF) to bit patterns of length 8.
Example:
a → 01100001 (0x61)
á → 11100001 (0xE1)
You can see all the mappings in this table.
UTF-8
Maps 1,112,064 characters (all existing Unicode code points) to bit patterns of either length 8, 16, 24, or 32 bits (that is, 1, 2, 3, or 4 bytes).
Example:
a → 01100001 (0x61)
á → 11000011 10100001 (0xC3 0xA1)
≠ → 11100010 10001001 10100000 (0xE2 0x89 0xA0)
😂 → 11110000 10011111 10011000 10000010 (0xF0 0x9F 0x98 0x82)
The way UTF-8 encodes characters to bit strings is very well described here.
Unicode and Encodings
Looking at the above examples, it becomes clear how Unicode is useful.
For example, if I'm Latin-1 and I want to explain my encoding of á, I don't need to say:
"I encode that a with an aigu (or however you call that rising bar) as 11100001"
But I can just say:
"I encode U+00E1 as 11100001"
And if I'm UTF-8, I can say:
"Me, in turn, I encode U+00E1 as 11000011 10100001"
And it's unambiguously clear to everybody which character we mean.
Now to the often arising confusion
It's true that sometimes the bit pattern of an encoding, if you interpret it as a binary number, is the same as the Unicode code point of this character.
For example:
ASCII encodes a as 1100001, which you can interpret as the hexadecimal number 0x61, and the Unicode code point of a is U+0061.
Latin-1 encodes á as 11100001, which you can interpret as the hexadecimal number 0xE1, and the Unicode code point of á is U+00E1.
Of course, this has been arranged like this on purpose for convenience. But you should look at it as a pure coincidence. The bit pattern used to represent a character in memory is not tied in any way to the Unicode code point of this character.
Nobody even says that you have to interpret a bit string like 11100001 as a binary number. Just look at it as the sequence of bits that Latin-1 uses to encode the character á.
Back to your question
The encoding used by your Python interpreter is UTF-8.
Here's what's going on in your examples:
Example 1
The following encodes the character á in UTF-8. This results in the bit string 11000011 10100001, which is saved in the variable a.
>>> a = 'á'
When you look at the value of a, its content 11000011 10100001 is formatted as the hex number 0xC3 0xA1 and output as '\xc3\xa1':
>>> a
'\xc3\xa1'
Example 2
The following saves the Unicode code point of á, which is U+00E1, in the variable ua (we don't know which data format Python uses internally to represent the code point U+00E1 in memory, and it's unimportant to us):
>>> ua = u'á'
When you look at the value of ua, Python tells you that it contains the code point U+00E1:
>>> ua
u'\xe1'
Example 3
The following encodes Unicode code point U+00E1 (representing character á) with UTF-8, which results in the bit pattern 11000011 10100001. Again, for output this bit pattern is represented as the hex number 0xC3 0xA1:
>>> ua.encode('utf-8')
'\xc3\xa1'
Example 4
The following encodes Unicode code point U+00E1 (representing character á) with Latin-1, which results in the bit pattern 11100001. For output, this bit pattern is represented as the hex number 0xE1, which by coincidence is the same as the initial code point U+00E1:
>>> ua.encode('latin1')
'\xe1'
There's no relation between the Unicode object ua and the Latin-1 encoding. That the code point of á is U+00E1 and the Latin-1 encoding of á is 0xE1 (if you interpret the bit pattern of the encoding as a binary number) is a pure coincidence.
Your terminal happens to be configured to UTF-8.
The fact that printing a works is a coincidence; you are writing raw UTF-8 bytes to the terminal. a is a value of length two, containing two bytes, hex values C3 and A1, while ua is a unicode value of length one, containing a codepoint U+00E1.
This difference in length is one major reason to use Unicode values; you cannot easily measure the number of text characters in a byte string; the len() of a byte string tells you how many bytes were used, not how many characters were encoded.
You can see the difference when you encode the unicode value to different output encodings:
>>> a = 'á'
>>> ua = u'á'
>>> ua.encode('utf8')
'\xc3\xa1'
>>> ua.encode('latin1')
'\xe1'
>>> a
'\xc3\xa1'
Note that the first 256 codepoints of the Unicode standard match the Latin 1 standard, so the U+00E1 codepoint is encoded to Latin 1 as a byte with hex value E1.
Furthermore, Python uses escape codes in representations of unicode and byte strings alike, and low code points that are not printable ASCII are represented using \x.. escape values as well. This is why a Unicode string with a code point between 128 and 255 looks just like the Latin 1 encoding. If you have a unicode string with codepoints beyond U+00FF a different escape sequence, \u.... is used instead, with a four-digit hex value.
It looks like you don't yet fully understand what the difference is between Unicode and an encoding. Please do read the following articles before you continue:
The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!) by Joel Spolsky
The Python Unicode HOWTO
Pragmatic Unicode by Ned Batchelder
When you define a as unicode, the chars a and á are equal. Otherwise á counts as two chars. Try len(a) and len(au). In addition to that, you may need to have the encoding when you work with other environments. For example if you use md5, you get different values for a and ua
I currently get a string as a parameters in my method,
i would like to extract the char in the I index and get it's hex value.
Currently i'm doing :
temp = string[i]
binascii.hexlify(temp);
but i get an error :
TypeError: 'str' does not support the buffer interface
Any ideas please ?
You need to encode the string to bytes:
binascii.hexlify(temp.encode('ascii'));
You'll need to pick a suitable encoding, one that can represent your text properly; I am presuming that your unicode characters fall in the 0-127 range here.
If you encode to a different encoding, the result will be a hex representation of that encoding. UTF-8 will use between 1 and 6 bytes per character for example.
Alternatively, you could use the ord() function and format the result to hex:
format(ord(temp), 'x')
and it'll work with any unicode character. It'll use the Unicode code point for the hex representation, so between 1 and 4 bytes (the latter for \Uabcdefgh wide characters). Depending on your maximum character width, you may want to pad the bytes to prevent ambiguous code points; say you need to encode up to codepoint \uffff then you'll need to use 2 bytes for every codepoint, or 4 hex characters:
format(ord(temp), '04x')