Convert bytes to int?
Question:
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?
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 bytes
must either be a bytes-like object or an iterable
producing bytes.
The byteorder
argument determines the byte order used to represent the
integer. If byteorder
is "big"
, the most significant byte is at the
beginning of the byte array. If byteorder
is "little"
, the most
significant byte is at the end of the byte array. To request the
native byte order of the host system, use sys.byteorder
as the byte
order value.
The signed
argument indicates whether two’s complement is used to
represent the integer.
## Examples:
int.from_bytes(b'x00x01', "big") # 1
int.from_bytes(b'x00x01', "little") # 256
int.from_bytes(b'x00x10', byteorder='little') # 4096
int.from_bytes(b'xfcx00', byteorder='big', signed=True) #-1024
int.from_bytes( bytes, byteorder, *, signed=False )
doesn’t work with me
I used function from this website, it works well
https://coderwall.com/p/x6xtxq/convert-bytes-to-int-or-int-to-bytes-in-python
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
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'@x04x1axa3xff'
>>> for b in bytelist:
... print(b) # 64 4 26 163 255
>>> [b for b in bytelist] # [64, 4, 26, 163, 255]
>>> bytelist[2] # 26
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.
list()
can be used to convert bytes to int (works in Python 3.7):
list(b'x03x04x05')
[3, 4, 5]
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
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?
Assuming you’re on at least 3.2, there’s a built in for this:
int.from_bytes
(bytes
,byteorder
, *,signed=False
)…
The argument
bytes
must either be a bytes-like object or an iterable
producing bytes.The
byteorder
argument determines the byte order used to represent the
integer. Ifbyteorder
is"big"
, the most significant byte is at the
beginning of the byte array. Ifbyteorder
is"little"
, the most
significant byte is at the end of the byte array. To request the
native byte order of the host system, usesys.byteorder
as the byte
order value.The
signed
argument indicates whether two’s complement is used to
represent the integer.
## Examples:
int.from_bytes(b'x00x01', "big") # 1
int.from_bytes(b'x00x01', "little") # 256
int.from_bytes(b'x00x10', byteorder='little') # 4096
int.from_bytes(b'xfcx00', byteorder='big', signed=True) #-1024
int.from_bytes( bytes, byteorder, *, signed=False )
doesn’t work with me
I used function from this website, it works well
https://coderwall.com/p/x6xtxq/convert-bytes-to-int-or-int-to-bytes-in-python
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
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'@x04x1axa3xff'
>>> for b in bytelist:
... print(b) # 64 4 26 163 255
>>> [b for b in bytelist] # [64, 4, 26, 163, 255]
>>> bytelist[2] # 26
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.
list()
can be used to convert bytes to int (works in Python 3.7):
list(b'x03x04x05')
[3, 4, 5]
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