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BytesThe data type has a numerical range of 0~255 (0x00~0xFF). A byte has 8 bits of data, that's why its maximum value is 0xFF. In some cases, you need to convert a byte or byte array to an integer for further data processing. Let's see how to convert a byte Bytesto an integer integer.

Bytes in Python 2.7Bytes

bytesThere is no built-in data type in Python 2.7 . The keywords byteare strequivalent to . We can isconclude this by the following .

>>> bytes is str
True

bytearrayUsed to define a bytesor an byte arrayobject.

>>> byteExample1 = bytearray([1])
>>> byteExample1
bytearray(b'\x01')
>>> byteExample2 = bytearray([1,2,3])
>>> byteExample2
bytearray(b'\x01\x02\x03')

Converting bytes to integers in Python 2.7

Python internal module structcan convert binary data (bytes) to integers. It can convert bytes (actually strings) and integers in Python 2.7 in both directions. Here is a basic introduction to it,

struct.unpack(fmt, string)
# Convert the string according to the given format `fmt` to integers. The result is a tuple even if there is only one item inside.

import struct

testBytes = b"\x00\x01\x00\x02"
testResult = struct.unpack(">HH", testBytes)
print testResult

(1, 2)

The format string >HHconsists of two parts,

1. >Indicates that binary data is big-endian, or in other words, the data is sorted from the high end (most significant bit). For example, \x00\0x1middle, \x00is the high byte, and \x01is the low byte.
2. HHIndicates that there are two objects of type in the byte string H. HIndicates that it is unsigned shortan integer, occupying 2 bytes.

You can get different results from the same string if the data is assigned in a different format.

>>> testResult = struct.unpack('<HH', testBytes)
>>> testResult
(256, 512)

Here, <indicates that the byte order is little-endian. Therefore \x00\x01becomes 00+1*256 = 256not 0*256+1 = 1.

>>> testResult = struct.unpack('<BBBB', testBytes)
>>> testResult
(0, 1, 0, 2)

Bindicates the data type unsigned char, and it occupies 1 byte. Therefore, it \x00\x01\x00\x02will be converted into 4 unsigned charvalues ​​instead of 2 unsigned shortvalues.

>>> testResult = struct.unpack('<BBB', b'\x00\x01\x00\x02')

Traceback (most recent call last):
  File "<pyshell#35>", line 1, in <module>
    testResult = struct.unpack('<BBB', b'\x00\x01\x00\x02')
error: unpack requires a string argument of length 3

You can check out structthe official documentation of the module for more information on format strings.

Bytes in Python 3Bytes

bytesIt is a built-in data type in Python 3, so you can bytesdefine bytes directly using the keyword.

>>> testByte = bytes(18)
>>> type(testByte)
<class 'bytes'>

You can also define one or more bytes directly as follows.

>>> testBytes = b'\x01\x21\31\41'
>>> type(testBytes)
<class 'bytes'>

Convert bytes to integers in Python 3

In addition to the module that was introduced in Python 2.7 struct, you can also use the new Python 3 built-in integer method to perform bytes-to-integer conversion, the int.from_bytes()method.

int.from_bytes()example

>>> testBytes = b'\xF1\x10'
>>> int.from_bytes(testBytes, byteorder='big')
61712

This byteorderoption is similar to struct.unpack()the definition of byte order format.

The byteorderoption is similar to struct.unpack()format byte order definition.

int.from_bytes()There is a third option signed, which assigns an integer type to signedor unsigned.

>>> testBytes = b'\xF1\x10'
>>> int.from_bytes(testBytes, byteorder='big', signed=True)
-3824

unsigned chartUsed when the byte is[]

If the data format is unsigned charand contains only one byte, you can directly access it using the object index to get the integer.

>>> testBytes = b'\xF1\x10'
>>> testBytes[0]
241
>>> testBytes[1]
16