Python problem

7.5 Grade Point Average (GPA)

Prompt the user for successive input lines, with the prompt "Enter course number, units, and grade, separated by spaces". So a sample input line might be "ECS10 4 B-". Continue to prompt until a blank line is entered, that is a line with nothing before the new line character, which will be read in by input() as an empty string. Then compute the GPA as a weighted average of the points assigned for each grade, weighted by the number of units. The point values of the grades are 4 for A, 3 for B, 2 for C, 1 for D, and 0 for F. Except for the grade A, where + has no effect, a + after the letter increases the point value by 0.3, and except for F, where a - has no effect, a - after a letter decreases the point value by 0.3, so, for example, B- is worth 3 - 0.3 = 2.7 points. The weighted points for a course is the point value of the grade, multiplied by the number of units for the course. The weighted average for the GPA is then the sum of these weighted points, divided by sum of the units. Print the GPA with exactly two decimal places, preceded by the text "The GPA is ". So a sample session might look like:

The arithmetic for the GPA in the above example would be

(4 * 2.7 + 4 * 2.3 + 3 * 4.0 + 2 * 1.0) / (4 + 4 + 3 + 2)