使用8位编码将二进制转换为字节数组

Question

I am writing code which create messages to be sent over a CANBUS using a particular protocol. An example format for a data field of such a message is:

[from_address (1 byte)][control_byte (1 byte)][identifier (3 bytes)][length (3 bytes)]

The data field needs to be formatted as a list or bytearray. My code currently does the following:

 data = dataFormat((from_address << 56)|(control_byte << 48)|(identifier << 24)|(length))

where dataFormat is defined as follows:

 def dataFormat(num):
     intermediary = BitArray(bin(num))
     return bytearray(intermediary.bytes)

This does exactly what I want it to, except for when from_address is a number that can be described in less than 8 bits. In these cases bin() returns a binary of character length not divisible by 8 (extraneous zeroes are discarded), and so intermediary.bytes complains that the conversion is ambiguous:

 InterpretError: Cannot interpret as bytes unambiguously - not multiple of 8 bits.

I am not tied to anything in the above code - any method to take a sequence of integers and convert it to a bytearray (with correct sizing in terms of bytes) would be greatly appreciated.

Answer 1

If it's a bytearray that you'd like, then the simple option would be to jump straight there and build it up directly. Something like this:

# Define some values:
from_address = 14
control_byte = 10
identifier = 80
length = 109

# Create a bytearray with 8 spaces:
message = bytearray(8)

# Add from and control:
message[0] = from_address
message[1] = control_byte

# Little endian dropping in of the identifier:
message[2] = identifier & 255
message[3] = (identifier >> 8) & 255
message[4] = (identifier >> 16) & 255

# Little endian dropping in of the length:
message[5] = length & 255
message[6] = (length >> 8) & 255
message[7] = (length >> 16) & 255

# Display bytes:
for value in message:
    print(value)

Here's a working example of that .

Health warning

The above assumes that the message is expected to be little endian . There may also be built in ways of doing this in Python, but it's not a language I use often.