I'm currently working on an encryption/decryption program and I need to be able to convert bytes to an integer. I know that:
bytes([3]) = b'\x03'
Yet I cannot find out how to do the inverse. What am I doing terribly wrong?
6 Answers
Assuming you're on at least 3.2, there's a built in for this:
int.from_bytes(bytes,byteorder, *,signed=False)...
The argument
bytesmust either be a bytes-like object or an iterable producing bytes.The
byteorderargument determines the byte order used to represent the integer. Ifbyteorderis"big", the most significant byte is at the beginning of the byte array. Ifbyteorderis"little", the most significant byte is at the end of the byte array. To request the native byte order of the host system, usesys.byteorderas the byte order value.The
signedargument indicates whether two’s complement is used to represent the integer.
## Examples:
int.from_bytes(b'\x00\x01', "big") # 1
int.from_bytes(b'\x00\x01', "little") # 256
int.from_bytes(b'\x00\x10', byteorder='little') # 4096
int.from_bytes(b'\xfc\x00', byteorder='big', signed=True) #-1024
Lists of bytes are subscriptable (at least in Python 3.6). This way you can retrieve the decimal value of each byte individually.
>>> intlist = [64, 4, 26, 163, 255]
>>> bytelist = bytes(intlist) # b'@\x04\x1a\xa3\xff'
>>> for b in bytelist:
... print(b) # 64 4 26 163 255
>>> [b for b in bytelist] # [64, 4, 26, 163, 255]
>>> bytelist[2] # 26
int.from_bytes( bytes, byteorder, *, signed=False )
doesn't work with me I used function from this website, it works well
def bytes_to_int(bytes):
result = 0
for b in bytes:
result = result * 256 + int(b)
return result
def int_to_bytes(value, length):
result = []
for i in range(0, length):
result.append(value >> (i * 8) & 0xff)
result.reverse()
return result
In case of working with buffered data I found this useful:
int.from_bytes([buf[0],buf[1],buf[2],buf[3]], "big")
Assuming that all elements in buf are 8-bit long.
An old question that I stumbled upon while looking for an existing solution. Rolled my own and thought I'd share because it allows you to create a 32-bit integer from a list of bytes, specifying an offset.
def bytes_to_int(bList, offset):
r = 0
for i in range(4):
d = 32 - ((i + 1) * 8)
r += bList[offset + i] << d
return r
list() can be used to convert bytes to int (works in Python 3.7):
list(b'\x03\x04\x05')
[3, 4, 5]
