exercise11_2.py

#!/usr/bin/env python3
"""
Exercise  11.2: Write a program to look for lines of the form

'New Revision: 39771'

and extract the number from each of the lines using a regular expression and
the findall() method. Compute the average of the numbers and print out the
average.

Enter file:mbox.txt
38549.7949721

Enter file:mbox-short.txt
39756.9259259

Python for Everybody: Exploring Data Using Python 3
by Charles R. Severance
"""
import re


rev = []
rev_ave = 0

fname = input('Enter file: ')
try:
    fhand = open(fname)
except FileNotFoundError:
    print('File cannot be opened: ', fname)
    exit()


for line in fhand:
    line = line.rstrip()
    rev_temp = re.findall('^New Revision: ([0-9.]+)', line)
    for val in rev_temp:
        val = float(val)            # Convert the strings to floats
        rev = rev + [val]           # Combine all values

rev_sum = sum(rev)
count = float(len(rev))
if count:
    rev_ave = rev_sum / count
print(rev_ave)