How To Convert Hex String To Float (little Endian)

I just learned Python (3.x) and I am stuck with HEX String conversion to Float. I have this HEX String values: '0x22354942F31AFA42CE6A494311518A43082CAF437C6BD4C35F78FA433BF10F442A

Solution 1:

Let's break things down here, because you seem to be confused a bit with all of the juggling of representations. You have some hexadecimal string (that's base 16 encoding) of some binary data. That's your 0x22354942F31AFA42CE6A494311.... You correctly identified that you can convert this from its encoded form to python bytes with bytes.fromhex:

hex_encoded = '0x22354942F31AFA42CE6A494311518A43082CAF437C6BD4C35F78FA433BF10F442A5222448D3D3544200749C438295C4468AF6E4406B4804450518A4423B0934450E99CC4'binary_data = bytes.fromhex(hex_encoded[2:])  # we do 2: to remove the leading '0x'

At this point, unless we know how binary_data was constructed we can't do anything. But we can take some guesses. You know the first few numbers are floating points: 50.3018875, 125.052635, 201.4172, .... Typically floats are encoded using the IEEE 754 standard. This provides 3 different encodings of a floating point number: binary16 (16 bits), float (32 bits), and double (64 bits). You can see these in the struct documentation, they are format codes 'e', 'f', and 'd', respectively. We can try each to see which of (if any) your binary data is encoded as. By trial and error, we discover your data was encoded as 32-bit floats, so you can decode them with:

FLOAT = 'f'
fmt = '<' + FLOAT * (len(binary_data) // struct.calcsize(FLOAT))
numbers = struct.unpack(fmt, binary_data)
print(numbers)

Why did what you tried not work? Well you used the format code 'H' which is for an unsigned short. This is an integer, which is why you were getting back numbers with no fractional part!