i am building a simple sync program,
whan the program starts it takes all the bandwith,
i need to set the speed limit,
i am using using ftplib

file = open(local_file_path, 'r')
    print ftp.storlines('STOR '+ file_name , file)

You could use a modified file object which sleeps between the lines. The following code works for me

# python 2
HOST, USER, PASSWD = "", "", "" # <--- your values here

from ftplib import FTP
from time import sleep

class SlowFile(object):
    def __init__(self, name, mode="r", delay = 0.1):
        self.src = open(name, mode)
        self.delay = delay
        
    def readline(self):
        line = self.src.readline()
        if line:
            sleep(self.delay) # sleep between the lines
        return line

def main():
    ftp = FTP(HOST, USER, PASSWD)
    try:
        name = "foo.txt"
        src = SlowFile(name, "r", delay = 0.2)
        ftp.storlines("STOR " + name, src)
    finally:
        ftp.quit()
    
if __name__ == "__main__":
    main()

This should be very slow. You may set the delay according to your file's size.

Grib. SlowFile.readline was not called therefore the delay will not work.
it should be like......

def main():
    ftp = FTP(HOST, USER, PASSWD)
    try:
        name = "foo.txt"
        src = SlowFile(name, "r", delay = 0.2)
        ftp.storlines("STOR " + name, src.readline()) # this part....
    finally:
        ftp.quit()
    
if __name__ == "__main__":
    main()

Grib. SlowFile.readline was not called therefore the delay will not work.
it should be like......

def main():
    ftp = FTP(HOST, USER, PASSWD)
    try:
        name = "foo.txt"
        src = SlowFile(name, "r", delay = 0.2)
        ftp.storlines("STOR " + name, src.readline()) # this part....
    finally:
        ftp.quit()
    
if __name__ == "__main__":
    main()

I don't think so: first, the code worked for me as it is, second, the second argument of ftp.storlines() is an open file object with a readline() method, according to the python documentation. In your snippet, you're passing a string (the first line of the file).