为什么 Python 字节数组的值 >= 256

Question

The Python documentation for bytearray states:

The bytearray type is a mutable sequence of integers in the range 0 <= x < 256.

However the following code suggests values can be >= 256. I store a 9 bit binary number which has a maximum value of: 2^9-1 = 512-1 = 511

ba = bytes([0b111111111])
print '%s' % (ba)

The 9 bit binary number is printed as decimal 511:

[511]

I don't know what the intended behavior is, but I assumed the most significant bit(s) would be dropped to give an 8 bit number.

Answer 1

You aren't actually creating a bytearray or a bytes object, you're just creating a string containing '[511]' , since bytes in Python 2 is just a synonym for str . In Python 3, you would get an error message:

ValueError: byte must be in range(0, 256)

The following code works in Python 2 or Python 3; note that I'm passing an 8 bit number, so it's in range.

ba = bytearray([0b11111111])
print(repr(ba))

output

bytearray(b'\xff')

Answer 2

code:

a = 511
byte = a.to_bytes(byte length goes here, 'little')

to decode:

a = int.from_bytes(byte, 'little')