WRITE PYTHON 3.x command line scripts. WRITE  A SINGLE FUNCTION. 
USE sys.argv, sys.stdin. 
HANDLE ERRORS. EXPLANATIONS MUST BE A COMMENT. 

# Start
# command line script. Read filename from args, open file, copy stdin to file
import sys

if (len(sys.argv) != 2:
  print("not_handled")
  sys.exit()

filename = sys.argv[1]
file = open(filename, 'w')
file.write(sys.stdin.read())
file.close()

# Done

# Start
#{{$input}}
# Read input sfrom stdin. print all output
