# Author:  James Tam
# Version: November 17 2011 (Python 3.X port)

# V2
# This version will convert the letter grade to a numerical
# GPA which will then be written to another (output) file.

# V1
# A program by James Tam that reads in letter grades from a file called
# 'letters.txt' and displays the grades onscreen.

# Get information about the file name at run time from the user.   
inputFileName = input ("Enter the name of input file to read the grades from: ")
outputFileName = input ("Enter the name of the output file to record the GPA's to: ")

# Open file for reading, confirm file with user.
inputFile = open (inputFileName, "r")
outputFile = open (outputFileName, "w")
   
# Update user on what is happening.
print("Opening file", inputFileName, " for reading.")
print("Opening file", outputFileName, " for writing.")
   
# While we haven't read past the end of the file continue reading from
# it.
gpa = 0
for line in inputFile:
    if (line[0] == "A"):
        gpa = 4
    elif (line[0] == "B"):
        gpa = 3
    elif (line[0] == "C"):
        gpa = 2
    elif (line[0] == "D"):
        gpa = 1
    elif (line[0] == "F"):
        gpa = 0
    else:
        gpa = -1

    # Add onto the end of the string the newline marker 
    # gpa on it's own line in the output file).
    temp = str (gpa)
    temp = temp + '\n'
    print (line[0], '\t', gpa)

    # Write the gpa (converted from a number to a string). Because the gpa is
    # followed by a newline each gpa will reside on it's own line in the output
    # file.
    outputFile.write (temp)

# Finished writing to file, provide feedback to user and close file.
inputFile.close ()
outputFile.close () 
print ("Completed reading of file", inputFileName)
print ("Completed writing to file", outputFileName)