Working with two's complement in Python

Question

I am using python as the main scripting language on a micro controller. The micro controller reads two 8-bit hex numbers from the I2C bus; for example:

out_L = C2
out_H = F2

Both these are received as strings in python. F2C2 represents a two's complement number. I need the decimal value of the number.

I can convert the hex strings to binary strings with

bin_out = "0b" + ( bin(int(hex_out, 16))[2:] ).zfill(8)

Now I have to convert the binary value to a decimal value which is where I am stuck. I first have to do two's complement convertion and then convert to decimal. Because the binary value is still a string I can't do normal binary operations on it and can't convert it to decimal. Please assist. All my efforts to correctly change the binary string to binary value provides me with the incorrect value.

Hongzheng · Accepted Answer · 2015-11-23 06:54:02Z

1

You may just apply the 2's compliment directly to the original int value:

out_L = "C2"
out_H = "F2"

hex_out = ''.join((out_H, out_L))
value = int(hex_out, 16) # value = 62146
if value> 0x7FFF:
    value -= 0x10000

print value # output -3390

answered Nov 23, 2015 at 6:54

Hongzheng

3654 silver badges10 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Aswin Murugesh · Accepted Answer · 2015-11-23 06:53:40Z

0

Convert binary to decimal in python by using:

int(binary_number,2)

answered Nov 23, 2015 at 6:53

Aswin Murugesh

11.1k11 gold badges46 silver badges73 bronze badges

1 Comment

Henro Ritchie Over a year ago

This also works - I somehow could not get it working earlier.

Collectives™ on Stack Overflow

Working with two's complement in Python

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related