CODEWITHSUNDEEP
python-3.xcastingarrays
user2236181
user2236181

Reputation: 21

Python3: Converting or 'Casting' byte array string from string to bytes array

New to this python thing. A little while ago I saved off output from an external device that was connected to a serial port as I would not be able to keep that device. I read in the data at the serial port as bytes with the intention of creating an emulator for that device. The data was saved one 'byte' per line to a file as example extract below.

b'\x9a'
b'X'
b'}'
b'}'
b'x'
b'\x8c'

I would like to read in each line from the data capture and append what would have been the original byte to a byte array. I have tried various append() and concatenation operations (+=) on a bytearray but the above lines are python string objects and these operations fail.

Is there an easy way (a built-in way?) to add each of the original byte values of these lines to a byte array?

Thanks.

M

Update I came across the .encode() string method and have created a crude function to meet my needs.

def string2byte(str):
    # the 'byte' string will consist of 5, 6 or 8 characters including the newline
    # as in b',' or b'\r' or b'\x0A'
    if len(str) == 5:
        return str[2].encode('Latin-1')
    elif len(str) == 6:
        return str[3].encode('Latin-1')
    else:
        return str[4:6].encode('Latin-1')

...well, it is functional.

If anyone knows of a more elegant solution perhaps you would be kind enough to post this.

Upvotes: 0

Views: 1044

Answers (1)

jfs
jfs

Reputation: 414079

b'\x9a' is a literal representation of the byte 0x9a in Python source code. If your file literally contains these seven characters b'\x9a' then it is bad because you could have saved it using only one byte. You could convert it to a byte using ast.literal_eval():

import ast

with open('input') as file:
    a = b"".join(map(ast.literal_eval, file)) # assume 1 byte literal per line

Upvotes: 1

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