How to convert int to bytes?

Question

How to convert int to bytes?

I work with the controller ESP8266 on the firmware MicroPython, I receive data on the bus I2C; to configure the controller, I need to send single bytes to write to registers.

Due to the fact that the functions working with I2С accept only objects of the bytes type for input/output, it is necessary to store the configuration data in this form, which is extremely inconvenient.

It looks like this:

__scales = {
    "0.88":[b'\x00', 0.73],
    "1.3": [b'\x20', 0.92],
    "1.9": [b'\x40', 1.22],
    "2.5": [b'\x60', 1.52],
    "4.0": [b'\x80', 2.27],
    "4.7": [b'\xA0', 2.56],
    "5.6": [b'\xC0', 3.03],
    "8.1": [b'\xE0', 4.35]}

Vriants of the solution:

Create a table of configuration parameters bytes in a tabular way, write to a file and forget.

The disadvantages of this solution: the frenzied volume of the table; extremely weak suitability for making modifications.

Work with data in numeric form. Create configuration parameters by applying masks.

For example:

>>> d = 0b00000000
>>> c = 0b10000001
>>> bin (c | (1 << 4))
'0b10010001'

This is where the problem arises: I do not know how to transform the resulting object of type int into an object of type bytes.

How do I do this myself? language?

2

python python-3.x micropython микроконтроллеры esp8266

Author: insolor, 2017-04-17

Source

1 answers

score 3 · Accepted Answer

Py3 has a special method just for this case int.to_bytes.

a = 123
a.to_bytes(8, byteorder='big', signed=true)
>>> b'\x00\x00\x00\x00\x00\x00\x00{'

The first argument is actually the number of bytes. If 8 is a lot, use as many as necessary.

Minus - not available on the second version.

There is another way out, which is suitable for all versions: module struct, which serializes simple types. To do this, use a special format table, in which you can also specify the size and order byte sequence (endiannes). For example, I is an unsigned integer of 4 bytes, and > is the BigEndian order. For 8 signed bytes, q:

import struct

a = 123

print(struct.pack(">q", a))

>>> b'\x00\x00\x00\x00\x00\x00\x00{'

Again, if 8 is a lot, then there is C, then there is char - 1 byte.