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I am working with Python3.2. I need to take a hex stream as an input and parse it at bit-level. So I used
bytes.fromhex(input_str)
to convert the string to actual bytes. Now how do I convert these bytes to bits?
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Getting the size of an integer Note that 1 byte equals 8 bits. Therefore, you can think that Python uses 24 bytes as an overhead for storing an integer object. It returns 28 bytes. Since 24 bytes is an overhead, Python uses 4 bytes to represent the number 100.
Let us see how to write bytes to a file in Python. First, open a file in binary write mode and then specify the contents to write in the form of bytes. Next, use the write function to write the byte contents to a binary file.
To convert from bits to bytes, simply divide the number of bits by 8. For example, 256 bits are equal to 256 / 8 = 32 bytes.
To convert bytes to int in Python, use the int. from_bytes() method. A byte value can be interchanged to an int value using the int. from_bytes() function.
Another way to do this is by using the bitstring module:
>>> from bitstring import BitArray >>> input_str = '0xff' >>> c = BitArray(hex=input_str) >>> c.bin '0b11111111' And if you need to strip the leading 0b:
>>> c.bin[2:] '11111111' The bitstring module isn't a requirement, as jcollado's answer shows, but it has lots of performant methods for turning input into bits and manipulating them. You might find this handy (or not), for example:
>>> c.uint 255 >>> c.invert() >>> c.bin[2:] '00000000' etc.
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Operations are much faster when you work at the integer level. In particular, converting to a string as suggested here is really slow.
If you want bit 7 and 8 only, use e.g.
val = (byte >> 6) & 3 (this is: shift the byte 6 bits to the right - dropping them. Then keep only the last two bits 3 is the number with the first two bits set...)
These can easily be translated into simple CPU operations that are super fast.
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