"""
7.2 Write a program that prompts for a file name, then opens that file and reads through the file
looking for lines of the form: X-DSPAM-Confidence:    0.8475
Count these lines and extract the floating point values from each of the lines and compute the average
of those values and produce an output as shown below. Do not use the sum() function or a variable named sum
in your solution.
You can download the sample data at http://www.py4e.com/code3/mbox-short.txt when you are testing below enter
 mbox-short.txt as the file name or it is in the github repository.
"""
# Use the file name mbox-short.txt as the file name
fname = input("Enter file name: ")
fh = open(fname)
Sumatoria=0
count=0
for line in fh:
    if not line.startswith("X-DSPAM-Confidence:") : continue
    l=line.rstrip()
    pos=l.find(" ")
    num=float(l[pos:])
    Sumatoria+=num
    count+=1
try:
    print("Average spam confidence:",Sumatoria/count)
except:
    print("Error: division por cero")