How to find and extract values from a txt file?

Question

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, 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.*

This is my code:

fname = input("Enter a file name:",)
fh = open(fname)
count = 0
# this variable is to add together all the 0.8745's in every line
num = 0
for ln in fh:
    ln = ln.rstrip()
    count += 1
    if not ln.startswith("X-DSPAM-Confidence:    ") : continue
    for num in fh:
        if ln.find(float(0.8475)) == -1:
            num += float(0.8475)
        if not ln.find(float(0.8475)) : break
    # problem: values aren't adding together and gq variable ends up being zero
gq = int(num)
jp = int(count)
avr = (gq)/(jp)
print ("Average spam confidence:",float(avr))

The problem is when I run the code it says there is an error because the value of num is zero. So I then receive this:

ZeroDivisionError: division by zero

When I change the initial value of num to None a similar problem occurs:

int() argument must be a string or a number, not 'NoneType'

This is also not accepted by the python COURSERA autograder when I put it at the top of the code:

from __future__ import division

The file name for the sample data they have given us is "mbox-short.txt". Here's a link http://www.py4e.com/code3/mbox-short.txt

Answer 1

I edited your code like below. I think your task is to find numbers next to X-DSPAM-Confidence: . And i used your code to identify the X-DSPAM-Confidence: line. Then I splitted the string by ':' then I took the 1st index and I converted to float.

fname = input("Enter a file name:",)
fh = open(fname)
count = 0
# this variable is to add together all the 0.8745's in every line
num = 0
for ln in fh:
    ln = ln.rstrip()
    if not ln.startswith("X-DSPAM-Confidence:") : continue
    count+=1 
    num += float(ln.split(":")[1])
gq = num
jp = count
avr = (gq)/(jp)
print ("Average spam confidence:",float(avr))

Answer 2

• Open files using with , so the file is automatically closed.
• See the in-line comments.
• Desired lines are in the form X-DSPAM-Confidence: 0.6961 , so split them on the space.
  • 'X-DSPAM-Confidence: 0.6961'.split(' ') creates a list with the number is at list index 1.

fname = input("Enter a file name:",)
with open(fname) as fh:
    count = 0
    num = 0  # collect and add each found value
    for ln in fh:
        ln = ln.rstrip()
        if not ln.startswith("X-DSPAM-Confidence:"):  # find this string or continue to next ln
            continue
        num += float(ln.split(' ')[1])  # split on the space and add the float
        count += 1  # increment count for each matching line
    avr = num / count  # compute average
    print(f"Average spam confidence: {avr}")  # print value