read from source file and write to target file line by line until the end of the source file. use a function to add the numbers in the source file and write to target file the sum.

def add(a, b):
  return a + b
    
def copy(sourceFileName, targetFileName):
  f = open(sourceFileName, 'r')
  g = open(targetFileName, 'w')
  nextLine = f.readline()
  while nextLine != "":
    g.write(nextLine)
    nextLine = f.readline()
  f.close()
  g.close()

def sum(sourceFileName, targetFileName):
  f = open(sourceFileName, 'r')
  g = open(targetFileName, 'w')
  nextLine = f.readline()
  s = 0
  while nextLine != "":
    nextLine = f.readline()
    s = s + int(nextLine)
  f.close()
  g.write("The sum of the numbers in the source file is ")
  g.writeline(s)
  g.close()