Send a single byte over TCP socket python

Question

I am trying to write a function in python 3.x that returns a single byte of data to send over a TCP connection.

The data I am trying to send is an unsigned integer from 0-100.

I am checking the bytes used by the data with sys.getsizeof(data), but I have not come across an instance where sys.getsizeof(data) == 1 .

lets say data = 10

I have tried several different ways to store a byte:

 1) struct.pack('>b', 10)

 2) bytes(10), bytes([10])

 3) 0x10

 4) bytearray(10)

 5) b'10'

all of these have returned over double digits in byte size.

I am looking for a way in python to send a single byte over a TCP socket.

If you only have a single byte, it doesn't matter if you have dozens of bytes of overhead, because you're only paying that overhead once. You have billions of bytes of memory. — user2357112
– user2357112, Commented Jan 3, 2018 at 17:43
Can you explain a little more? Sure its not using those bytes, but I don't want the overhead because of space constraints. — Jake
– Jake, Commented Jan 3, 2018 at 17:43
Now, if you're calling this function more than once, so you have a bunch of bytes to store, then store them together in the same bytearray. — user2357112
– user2357112, Commented Jan 3, 2018 at 17:44
Python objects don't work like that. You can't just have a sigle byte, or a single machine integer, you always get a fully-fledged object, with the overhead that comes with that. Perhaps you should explain what you're really trying to do. For example, if you need to pass a byte from Python to a library written in C, then there's a way to do that. — PM 2Ring
– PM 2Ring, Commented Jan 3, 2018 at 17:48

Robᵩ · Accepted Answer · 2018-01-03 18:03:58Z

5

Answering OP's underlying question:

I am trying to send that single byte over a TCP socket.

The Python representation that you use to hold your byte is irrelevant. You don't send a copy of Python object, you send the value contained in the Python object. Since socket.send() requires a buffer or string, I'd have your function return a bytestring: b'\x0a' should work.

Here is a simple client program that sends exactly one byte to a server:

import socket

def return_one_byte():
    return b'\x10'

s = socket.socket()
s.connect(('localhost', 1234))
s.send(return_one_byte())
s.close()

edited Jan 3, 2018 at 18:03

answered Jan 3, 2018 at 17:58

Robᵩ

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user10495809 · Accepted Answer · 2018-10-12 15:06:17Z

Python is not like C or C++. Python inherently has high overhead. You can not store data in memory, but instead, get a fully-fledged object that is stored in memory.

When you try things like

 1) struct.pack('>b', 10)
 2) bytes(10), bytes([10])
 3) 0x10
 4) bytearray(10)
 5) b'10'

These are not storing bytes directly to memory, they are creating python objects to store byte data in. Thats why sys.getsizeof(data) != 1.

That being said there is a way around this to answer the underlying question. socket.send() requires a buffer or string and python has byte-strings. so socket.send('\x0a') would send exactly one byte. You could also return a byte string from a function.

def return_byte_string():
    return b'\x0a'

Then this could be passed into socket.send(return_byte_string()) to send a single byte over a TCP connection.

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