# Read a two-dimensional array from a file, then 
# compute the weighted average of the first column
# using the weights in the second column.
# Use two methods read_2d_array and weighted_ave.

# Define method to read values of two-dimensional 
# array from an input file.  Fields beyond 0 and 1
# are ignormed.
def read_2d_array(the_filename):
    data = [ ]
    f = open(the_filename, "r")
    line = f.readline( )
    while line:
        fields = line.split(",")
        value = float(fields[0].strip( ))
        weight = float(fields[1].strip( ))
        data.append([value, weight])
        line = f.readline( )
        
    return data

# Define method to compute weighted average of
# values in a data matrix.  The values are in
# column 0 and the weights are in column 1.
# Here is the formula for the weighted average:
# weighted_ave = 
#   (sum of value * weight) / (sum of weights)
def weighted_ave(the_data_array):
    sum_weighted_values = 0.0
    sum_weights = 0.0
    for row in the_data_array:
        sum_weighted_values += row[0] * row[1]
        sum_weights += row[1]

    return sum_weighted_values / sum_weights

# Use methods to compute weighted average 
# of values in file
data = read_2d_array("course-scores.txt")
print("Course Score: {0:.2f}".format(weighted_ave(data)))