We Keep Coding

How to decode a string representation of a bytes object?

I have a string which includes encoded bytes inside it:
str1 = "b'Output file \xeb\xac\xb8\xed\x95\xad\xeb\xb6\x84\xec\x84\x9d.xlsx Created'"
I want to decode it, but I can't since it has become a string. Therefore I want to ask whether there is any way I can convert it into
str2 = b'Output file \xeb\xac\xb8\xed\x95\xad\xeb\xb6\x84\xec\x84\x9d.xlsx Created'
Here str2 is a bytes object which I can decode easily using
str2.decode('utf-8')
to get the final result:
'Output file 문항분석.xlsx Created'

You could use ast.literal_eval:
>>> print(str1)
b'Output file \xeb\xac\xb8\xed\x95\xad\xeb\xb6\x84\xec\x84\x9d.xlsx Created'
>>> type(str1)
<class 'str'>
>>> from ast import literal_eval
>>> literal_eval(str1).decode('utf-8')
'Output file 문항분석.xlsx Created'

Based on the SyntaxError mentioned in your comments, you may be having a testing issue when attempting to print due to the fact that stdout is set to ascii in your console (and you may also find that your console does not support some of the characters you may be trying to print). You can try something like the following to set sys.stdout to utf-8 and see what your console will print (just using string slice and encode below to get bytes rather than the ast.literal_eval approach that has already been suggested):
import codecs
import sys
sys.stdout = codecs.getwriter('utf-8')(sys.stdout.buffer)
s = "b'Output file \xeb\xac\xb8\xed\x95\xad\xeb\xb6\x84\xec\x84\x9d.xlsx Created'"
b = s[2:-1].encode().decode('utf-8')

A simple way is to assume that all the characters of the initial strings are in the [0,256) range and map to the same Unicode value, which means that it is a Latin1 encoded string.
The conversion is then trivial:
str1[2:-1].encode('Latin1').decode('utf8')

Finally I have found an answer where i use a function to cast a string to bytes without encoding.Given string
str1 = "b'Output file \xeb\xac\xb8\xed\x95\xad\xeb\xb6\x84\xec\x84\x9d.xlsx Created'"
now i take only actual encoded text inside of it
str1[2:-1]
and pass this to the function which convert the string to bytes without encoding its values
import struct
def rawbytes(s):
"""Convert a string to raw bytes without encoding"""
outlist = []
for cp in s:
num = ord(cp)
if num < 255:
outlist.append(struct.pack('B', num))
elif num < 65535:
outlist.append(struct.pack('>H', num))
else:
b = (num & 0xFF0000) >> 16
H = num & 0xFFFF
outlist.append(struct.pack('>bH', b, H))
return b''.join(outlist)
So, calling the function would convert it to bytes which then is decoded
rawbytes(str1[2:-1]).decode('utf-8')
will give the correct output
'Output file 문항분석.xlsx Created'

Python hex IP as string to DDN IP string

I have the following IP in hex: 0xac141315
I would like to convert it to its DDN equivalent.
I used to use '.'.join([str(x) for x in 0xac141315.asNumbers()]) when 0xac141315 had the following type: <class 'CiscoNetworkAddress'>
Or is there a way to convert the string back to CiscoNetworkAddress?

According to CISCO-TC MIB, CiscoNetworkAddress is actually an octet string. There are many ways to turn octet string into a DDN. For example, with ipaddress module from Python 3 stdlib:
>>> from pysnmp.hlapi import OctetString
>>> ip = OctetString(hexValue='ac141315') # this is what you have
>>>
>>> ipaddress.IPv4Address(ip.asOctets())
IPv4Address('172.20.19.21')
Or you can turn it into SNMP SMI IP address:
>>> from pysnmp.hlapi import IpAddress
>>> IpAddress(ip.asOctets()).prettyPrint()
'172.20.19.21'
Also, you could get a sequence of integer octets right from your existing object:
>>> ip.asNumbers()
(172, 20, 19, 21)
Keep in mind, that CiscoNetworkAddress is designed to hold many different address types, not just IPv4. So you should probably apply the IPv4 conversion only when it's actually IPv4 address.

Here is a complete example of how to convert to decimal ip:
#!/usr/bin/python
import sys
# Must be (0xXXXXXXXX)
if len(sys.argv)< 2:
print("Usage: %s (HEX FORMAT, for example 0xAC141315)" % sys.argv[0])
sys.exit(0)
user_option = sys.argv[1]
hex_data=user_option[2:]
#Check if length = 8
if len(hex_data)< 8:
hex_data = ''.join(('0',hex_data))
def hex_to_ip_decimal(hex_data):
ipaddr = "%i.%i.%i.%i" % (int(hex_data[0:2],16),int(hex_data[2:4],16),int(hex_data[4:6],16),int(hex_data[6:8],16))
return ipaddr
result=hex_to_ip_decimal(hex_data)
print result

How to decode base64 in python3

I have a base64 encrypt code, and I can't decode in python3.5
import base64
code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA" # Unencrypt is 202cb962ac59075b964b07152d234b70
base64.b64decode(code)
Result:
binascii.Error: Incorrect padding
But same website(base64decode) can decode it,
Please anybody can tell me why, and how to use python3.5 decode it?
Thanks

Base64 needs a string with length multiple of 4. If the string is short, it is padded with 1 to 3 =.
import base64
code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA="
base64.b64decode(code)
# b'admin:202cb962ac59075b964b07152d234b70'

According to this answer, you can just add the required padding.
code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA"
b64_string = code
b64_string += "=" * ((4 - len(b64_string) % 4) % 4)
base64.b64decode(b64_string) #'admin:202cb962ac59075b964b07152d234b70'

I tried the other way around. If you know what the unencrypted value is:
>>> import base64
>>> unencoded = b'202cb962ac59075b964b07152d234b70'
>>> encoded = base64.b64encode(unencoded)
>>> print(encoded)
b'MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA='
>>> decoded = base64.b64decode(encoded)
>>> print(decoded)
b'202cb962ac59075b964b07152d234b70'
Now you see the correct padding. b'MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA=

It actually seems to just be that code is incorrectly padded (code is incomplete)
import base64
code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA"
base64.b64decode(code+"=")
returns b'admin:202cb962ac59075b964b07152d234b70'

Python struct string to bin

I´m learning Python.
Seeing the module struct, I found a doubt:
Is it possible to convert a "string" to "bin" without giving the length.
For the case (with chars length)
F = open("data.bin", "wb")
import struct
data = struct.pack("24s",b"This is an unknown string")
print(data)
F.write(data)
F.close()
I´m trying to do the same but with unknown length.
Thanks a lot!

If you have the string, use len to determine the length of the string.
i.e
data = struct.pack("{0}s".format(len(unknown_string)), unknown_string)

The Bytes type is a binary data type, it just stores a bunch of 8bit characters. Note that the code with struct.pack ends up creating a bytes object:
>>> import struct
>>> data = struct.pack("24s",b"This is an unknown string")
>>> type(data)
<class 'bytes'>
>>> len(data)
24
The length of this is 24 as per your format specifier. If you just want to place the bytes-string directly into the file without doing any length checking you don't even need to use the struct module, you can just write it directly to the file:
F = open("data.bin", "wb")
F.write(b"This will work")
If however you wanted to keep the 24 bytes length you could keep using struct.pack:
>>> data = struct.pack("24s",b"This is an unknown st")
>>> len(data)
24
>>> print(data)
b'This is an unknown st\x00\x00\x00'
>>> data = struct.pack("24s",b"This is an unknown string abcdef")
>>> print(data)
b'This is an unknown strin'
In the case of supplying a bytes that is too short struct.pack pads the remainder with 0's and in the case where it's too long it truncates it.
If you don't mind getting the missing space padded out with zeros you can just pass in the bytes object directly to struct.pack and it will handle it.

Thanks to both...
My new code:
F = open("data.bin", "wb")
strs = b"This is an unkown string"
import struct
data = struct.pack("{0}s".format(len(strs)),strs)
print(data)
F.write(data)
F.close()

Print python os.urandom output on terminal

how can i print the output of os.urandom(n) in terminal?
I try to generate a SECRET_KEY with fabfile and will output the 24 bytes.
Example how i implement both variants in the python shell:
>>> import os
>>> out = os.urandom(24)
>>> out
'oS\xf8\xf4\xe2\xc8\xda\xe3\x7f\xc75*\x83\xb1\x06\x8c\x85\xa4\xa7piE\xd6I'
>>> print out
oS�������5*������piE�I

If what you want is hex-encoded string, use binascii.a2b_hex (or hexlify):
>>> out = 'oS\xf8\xf4\xe2\xc8\xda\xe3\x7f\xc75*\x83\xb1\x06\x8c\x85\xa4\xa7piE\xd6I'
>>> import binascii
>>> print binascii.hexlify(out)
6f53f8f4e2c8dae37fc7352a83b1068c85a4a7706945d649

To use just built-ins, you can get the integer value with ord and then convert that back to a hex number:
list_of_hex = [str(hex(ord(z)))[2:] for z in out]
print " ".join(list_of_hex)
If you just want the hex list, then the str() and [2:] are unnecessary
The output of this and the hexify() version are both type str and should work fine for the web app.