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Converting an integer intto a byte bytesis the inverse of bytesconverting a byte to an integer . Most of the to methods intdescribed in this article are the inverse of the to methods.intbytesbytesint

Generic method for converting intto in Python 2.7 and 3bytes

You can use the struct function in the Python module packto convert integers to bytes in a specific format.

>>> import struct
>>> struct.pack("B", 2)
'\x02'
>>> struct.pack(">H", 2)
'\x00\x02'
>>> struct.pack("<H", 2)
'\x02\x00'

struct.packThe first argument in the function is the format string, which specifies the byte format such as length, byte order (little/big endian), etc.

New conversion method from intto introduced in Python 3bytes

Use bytesto convert inttobytes

As mentioned in the previous article, bytesit is a built-in data type in Python 3. You can byteseasily convert integers 0 to 255 to byte data types using .

>>> bytes([2])
b'\x02'

int.to_bytes()Convert integer to byte type by

A new integer class method was introduced in Python 3.1 int.to_bytes(). It is the reverse conversion method discussed in the previous article int.from_bytes().

>>> (258).to_bytes(2, byteorder="little")
b'\x02\x01'
>>> (258).to_bytes(2, byteorder="big")
b'\x01\x02'
>>> (258).to_bytes(4, byteorder="little", signed=True)
b'\x02\x01\x00\x00'
>>> (-258).to_bytes(4, byteorder="little", signed=True)
b'\xfe\xfe\xff\xff'

The first argument is the length of the converted byte data, the second argument byteorderdefines the byte order as little or big-endian, and the optional argument signeddetermines whether to use two's complement to represent integers.

Running speed comparison

In Python 3, you have three ways to convert intto bytes,

• bytes()method
• struct.pack()method
• int.to_bytes()method

We will measure the execution time of each method to compare their performance, and finally provide suggestions for making the program run faster.

>>> import timeint
>>> timeit.timeit('bytes([255])', number=1000000)
0.31296982169325455
>>> timeit.timeit('struct.pack("B", 255)', setup='import struct', number=1000000)
0.2640925447800839
>>> timeit.timeit('(255).to_bytes(1, byteorder="little")', number=1000000)
0.5622947660224895

Therefore, use struct.pack()the function execute to perform integer-to-byte conversion for best performance, although it has been introduced in Python 2, old still has its uses!