Combining two bytes in Python

Question

I have a problem where I get two bytes represented as an int from 0-255, two bytes are supposed to represent one value. Right now I am doing it like this, but it takes way to a long time. Any tips?

bin_string = '0b' + bin(int(second_byte))[2:].zfill(8) + bin(int(first_byte))[2:].zfill(8)
result = float(literal_eval(bin_string))

example: 
203 -> 11001011
101 -> 01100101
-> 1100101101100101 -> 52069

I feel like there could be a simple mathematical formula but I cannot seem to figure it out ...

Possible duplicate of How do you combine two bytes in python? — Georgy
– Georgy, Commented Mar 18, 2019 at 11:02

meowgoesthedog · Accepted Answer · 2019-03-18 10:36:54Z

5

Left-shift the second byte by 8 bits and bitwise OR it with the first byte:

(second_byte << 8) | first_byte

For extra safety clamp both bytes to [0, 255] with a bitwise AND:

((second_byte & 0xFF) << 8) | (first_byte & 0xFF)

answered Mar 18, 2019 at 10:36

meowgoesthedog

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GBrandt · Accepted Answer · 2019-03-18 10:37:21Z

0

Binary shift operator:

(second_byte << 8) + first_byte

Same as:

second_byte * 256 + first_byte

answered Mar 18, 2019 at 10:37

GBrandt

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Alfe · Accepted Answer · 2019-03-18 10:37:45Z

0

If you get your bytes in a bytes value, i. e. a string of bytes, or if you want to put your bytes into one, then you should have a look at the struct module:

 struct.unpack('h', b'\x00\x01')

will return (256,) which is a tuple of all the unpacked stuff from the string b'\x00\x01' according to the format 'h'.

answered Mar 18, 2019 at 10:37

Alfe

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