How to convert bytes in a string back to bytes

Question

I understand that there are similar questions, but I do not understand them so here goes: I have bytes (encoded from a string) in a string form (read from a file). When I try to decode the bytes, I get an error saying that it is a string, not bytes. I understand it is in the wrong form, but do I not have the correct information? How can I convert bytes in a string back to bytes? I will also note I know this is not a secure password method and will not be used as one. (I am using python 3)

I've done some research into how I can fix this, but I am very new and either did not understand it or could not apply it. I though this would work but it does not:

password=bytes(password, 'cp037')

Oh well. Here is a short version of the code I have:

#writing to the file
password="example" 
password=password.encode('cp037') 
password=str(password)
f=open("passwordFile.txt", "w+")
f.write(password)
f.close

#reading from the file
f=open("passwordFile.txt","r")
password=f.read()
#this is where I need to turn password back into bytes
password=password.decode('cp037') 
print(password)

I expected to get example as output, but have a error: AttributeError: 'str' object has no attribute 'decode'

Answer 1

A quick possibility to convert from a string representation of bytes literals

"b'\x85\xa7\x81\x94\x97\x93\x85'"

to the actual bytes would be

bytes_as_bytes = eval(bytes_literals_as_str)

ie

bytes_as_bytes = eval("b'\\x85\\xa7\\x81\\x94\\x97\\x93\\x85'")

Answer 2

write byte, read byte and convert into string using decode

#writing to the file
password="example"
password=password.encode('cp037')
#password=str(password) (remove this line)
f=open("passwordFile.txt", "wb")
f.write(password)
f.close()

#reading from the file
f=open("passwordFile.txt","rb")
password=f.read()
#this is where I need to turn password back into bytes
y=password.decode('cp037')
print(y)

Answer 3

The simplest solution is to write the password as bytes object without converting it to str .

But anyway, the problem here is you've wrote a byte codded string, so the file will contains this b'\x85\xa7\x81\x94\x97\x93\x85' .

And when you read the line, it is actually an str , if you want to decode it you need to convert the encoded byte array to an actual bytes object , ~~I don't know if there is a ready-to-use function in python that allows to do that,~~ but one possible solution is to convert the line to a Hex coded line (by removing the b' from the beginning, and all the \x s, and the last quote ' ).

#writing to the file
password="example" 
password=password.encode('cp037') 
password=str(password)
f=open("passwordFile.txt", "w+")
f.write(password)
f.close()

#reading from the file
f=open("passwordFile.txt","r")
password=f.read()
#this is where I need to turn password back into bytes
# -------
# we converts the string 
# from "b'\x85\xa7\x81\x94\x97\x93\x85'" 
# to "85a78194979385"
# then pass it to the bytes.fromhex to get the bytes objet.
password=bytes.fromhex(password[2:-1].replace('\\x', '')).decode('cp037')
# -------
print(password)

Answer 4

Use hex() and fromhex() methods. Even if you convert to string (to simulate writing to a file, it works.)

Btw, this is just a password hashing example.

from hashlib import scrypt
from os import urandom

secret = "password"
salt = urandom(16).hex()

def hashing(secret, salt):
    return scrypt(secret.encode(), salt=salt.encode(), n=16384, r=8, p=1)

def checking(attempt, real_secret, salt):
    return real_secret == hashing(attempt, salt)

hashed = hashing(secret, salt)

# convert to hex, save it (convert to string) and convert it back to hex and then to bytes
new = hashed.hex() # convert it to hex
new = str(new) # simulate writing to a file
new = bytes.fromhex(new) # convert it back to bytes from hex/str type
print(checking(secret, new, salt)) # just testing if the conversion worked properly by checking if the passwords match