User defined writefile function won't save output to txt file

Question

I've created two functions to read and write text files as a larger part of a caeser cipher program where I need to encode and decode content from and to different text files. These are:

def readfile(f):
   try:
      file_object = open(f, 'r+')
      message = file_object.read()
      file_object.close()
      return message
   except:
      print("No such file or dictionary!")
      quit()

and

def writefile(message):
   try:
      f = open("file", 'a')
      f.write(message + '\n')
      f.close()
   except ValueError:
      print("No such file or dictionary!")
      quit()
   except:
      print("Input must be a string!")
      quit()

The problem seems to be that my write function won't actually save the program's output to the next text file. I've been stumped for sometime, could use a hand.

EDIT Thanks Barmar! my write function was writing to a set file that didn't exist. This worked for me:

def writefile(message):
   try:
      f = open(input("Please enter a file for writing:"), 'w')
      f.write(message + '\n')
      f.close()
   except ValueError:
      print("The selected file cannot be open for writing!")
      quit()
   except:
      quit()

Answer 1

Thanks Barmar! my write function was writing to a set file that didn't exist. This worked for me:

def writefile(message):
   try:
      f = open(input("Please enter a file for writing:"), 'w')
      f.write(message + '\n')
      f.close()
   except ValueError:
      print("The selected file cannot be open for writing!")
      quit()
   except:
      quit()