Python 3
I want to send a binary string over a socket. I am using
socket.send(b"Hello from {0}",client_id)
however I find the it is not properly substitution clientid.
what am I doing wrong? I do I accomplish this in a binary string
{0} is a placeholder for the str.format method, which you should be using, but bytes objects do not have a format method; instead, you can format it as a string first and then convert it to bytes with the encode method:
socket.send("Hello from {0}".format(client_id).encode())
Related
I have a question regarding the interpretation of a string as bytes
Within python, I have the situation that one variable contains e.g. this value
"bytearray(b'\x13\x02US')"
this is unfortunately due to the behavior of a module I am using. My question is, how could i get this string into bytes?
I have tried stripping away the "bytearray(b'" and the "')" at the end, and use .encode() as a function, but the result then is:
b'\\x13\\x02US'
Which clearly escapes the \ in order to prevent the interpretation as bytes.
How could i get this converted into
b'\x13\x02US'
instead though?
Thank you very much!
You could use .decode().replace('\\', '\'), this way it replaces the double slashes with single ones. Either attache it after your .encode() function or do it on your string seperately.
i currently pack hex number in little endian with struct.pack() or p32() from pwnlib, i always got bytes object output.
b'\xde\xad\xbe\xef'
i tried str.decode('utf-8') but in some case there is error output.
is there a way to decode this ?
im using python3 and pwntools 4.3
The byte object prefix is important, it is wrong to delete it.
It is just a python-internal representation of the object. If you need it to write a C string containing the same bytes, you should write a function for it, or encode it using hex escapes or octal escapes.
In python 3 bytes is not text. It is a sequence of octets, array of bytes.
Text is a sequence of unicode codepoints, like unicode type in python 2.
'\xaa' is just a shorthand for '\u00aa', and the shorthand is only creating confusion, so avoid it if possible. Use bytes objects where you mean binary data and unicode string text objects where you mean text.
See https://github.com/Gallopsled/pwntools-tutorial/blob/master/bytes.md
Python 3.6
I converted a string from utf8 to this:
b'\xe6\x88\x91\xe6\xb2\xa1\xe6\x9c\x89\xe7\x94\xb5#xn--ssdcsrs-2e1xt16k.com.au'
I now want that chunk of ascii back into string form, so there is no longer the little b for bytes at the beginning.
BUT I don't want it converted back to UTF8, I want that same sequence of characters that you ses above in my Python string.
How can I do so? All I can find are ways of converting bytes to string along with encoding or decoding.
The (wrong) answer is quite simple:
chr(asciiCode)
In your special case:
myString = ""
for char in b'\xe6\x88\x91\xe6\xb2\xa1\xe6\x9c\x89\xe7\x94\xb5#xn--ssdcsrs-2e1xt16k.com.au':
myString+=chr(char)
print(myString)
gives:
æ没æçµ#xn--ssdcsrs-2e1xt16k.com.au
Maybe you are also interested in the right answer? It will probably not please you, because it says you have ALWAYS to deal with encoding/decoding ... because myString is now both UTF-8 and ASCII at the same time (exactly as it already was before you have "converted" it to ASCII).
Notice that how myString shows up when you print it will depend on the implicit encoding/decoding used by print.
In other words ...
there is NO WAY to avoid encoding/decoding
but there is a way of doing it a not explicit way.
I suppose that reading my answer provided HERE: Converting UTF-8 (in literal) to Umlaute will help you much in understanding the whole encoding/decoding thing.
What you have there is not ASCII, as it contains for instance the byte \xe6, which is higher than 127. It's still UTF8.
The representation of the string (with the 'b' at the start, then a ', then a '\', ...), that is ASCII. You get it with repr(yourstring). But the contents of the string that you're printing is UTF8.
But I don't think you need to turn that back into an UTF8 string, but it may depend on the rest of your code.
I have an error message that was built using PyUnicode_FromString. I need to pass this message to PyErr_SetString. Is there an equivalence to PyBytes_AsString for unicode to convert it back to an Ascii character string?
Since you have an object for the message, use PyErr_SetObject() instead.
I've contered a Python 2 code to Python 3.
In doing so, I've changed
print 'String: ' + somestring
into
print(b'String: '+somestring)
because I was getting the following error:
Can't convert 'bytes' object to str implicitly
But then now I can't implement string attributes such as strip(), because they are no longer treated as strings...
global name 'strip' is not defined
for
if strip(somestring)=="":
How should I solve this dilemma between switching string to bytes and being able to use string attributes? Is there a workaround?
Please help me out and thank you in advance..
There are two issues here, one of which is the actual issue, the other is confusing you, but not an actual issue. Firstly:
Your string is a bytes object, ie a string of 8-bit bytes. Python 3 handles this differently from text, which is Unicode. Where do you get the string from? Since you want to treat it as text, you should probably convert it to a str-object, which is used to handle text. This is typically done with the .decode() function, ie:
somestring.decode('UTF-8')
Although calling str() also works:
str(somestring, 'UTF8')
(Note that your decoding might be something else than UTF8)
However, this is not your actual question. Your actual question is how to strip a bytes string. And the asnwer is that you do that the same way as you string a text-string:
somestring.strip()
There is no strip() builtin in either Python 2 or Python 3. There is a strip-function in the string module in Python 2:
from string import strip
But it hasn't been good practice to use that since strings got a strip() method, which is like ten years or so now. So in Python 3 it is gone.
>>> b'foo '.strip()
b'foo'
Works just fine.
If what you're dealing with is text, though, you probably should just have an actual str object, not a bytes object.
I believe you can use the "str" function to cast it to a string
print str(somestring).strip()
or maybe
print str(somestring, "utf-8").strip()
However, if the object is already a string, you don't get a new one. So if you're not sure whether an object is a string and need it to be and call str(obj), you won't create another if it's already a string.
x='123'
id(x)
2075707536496
y=str(x)
id(y)
2075707536496