I'm working on the internet connection programming, including Server and Client Socket, FTP, SMTP. But there is an error that depending on internet connection condition that I must handle it. But I don't know what the ConnnectionAbortedError, ConnectionRefusedError and ConnectionResetError do. And whether to catch an exception. I definitely understand that TimeoutError is catch for the connection is not respond for long time then raise an error. But I can't identify what are the three connection errors on above do.

FTPManager.py module for using in another module.

from ftplib import *

blockSize = 1024

host = "localhost"
instance = None

def login():
  global instance
  while True:
    try:
      instance = FTP(host)
      instance.login(user="NetPro",passwd="12345678")
      instance.retrlines("LIST")
      instance.cwd("Final Assignment")
      print("FTP Connected!")
      break
    except TimeoutError:
      print("FTP Login Timeout Error. Retrying...")

def logout():
  global instance
  instance.quit()

def changeDirectory(directory):
  global instance
  instance.cwd(directory)
  instance.retrlines("LIST")

def listAllFiles():
  global instance
  return instance.nlst()

def isFileExists(filename):
  global instance
  fileList = instance.nlst()
  if filename in fileList:
    return True
  return False

def downloadFile(filename):
  while True:
    try:
      with open(filename,"wb") as f:
        instance.retrbinary("RETR " + filename, f.write, blockSize)
      print("Download file " + filename + " completed.")
      break
    except ConnectionRefusedError:
      print("FTP Connection has been aborted.")
      login()

def uploadFile(filename):
  while True:
    try:
      with open(filename,"rb") as f:
        instance.storbinary("STOR " + filename, f, blockSize)
      print("Upload file " + filename + " completed.")
      break
    except ConnectionAbortedError:
      print("FTP Connection has been aborted.")
      login()

login()

The error exception is also used in SMTPManager.py for handling the internet connection error.

Thank you. Any help is appreciated.