python 3.x - Run one .py file from another .py file -

I have created a program that calculates the size of files I have created another program that sends mail to the user. Program names are filesize.py and mailsend.py respectively. Mailsend.py is working perfectly, when I run it, I can see the mail in my Gmail inbox. But I want to run this code from mailsend.py filesize.py

I have done this file in filesize.py: (I'm sure what I'm trying to do is stupid, but I Programming is the only dragon)

  import Mailsend.py cmd = "python mailsend.py" os.system (cmd)   
 and this does not work Any suggestions?   
 
 
 Change  Import mailsend.py  to  import os .  
 The recommended method is ...  
  mailsend.py   
  DIF main (): # old ` Mailseng 'content here if __name__ ==' __main__ ': main ()   
  filesize.py   
  import mailed mails .man ()