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 …

py4e_ex_07_02

# Use the file name mbox-short.txt as the file name
fname = input("Enter file name: ")
fhand = open(fname)

count = 0
for line in fhand:
    if line.startswith("X-DSPAM-Confidence:") : 
        count = count + 1

total = 0
for line in fhand:
    if line.startswith("X-DSPAM-Confidence:"):
       line = float(line[21:])
       total = line + total
       
average = total/ count

print("Average spam confidence:",average)

could you please explain the concept of float(line[21:]) and how did that total thing work?

it is basically string slicing. it means it will take the data in the string from the 21st character to the end of the string since we have not given any end. if we had specified like [21:30] so it will take the 21st character to 29th character.

fname = input("Enter file name: ")
try:
fh = open(fname)
except:
print("FILE NOT FOUND..!")
quit()

total = 0
count = 0
for line in fh:
if line.startswith("X-DSPAM-Confidence:"):
count = count + 1
line = float(line[20:26])
total = line + total

average = total / count

print("Average spam confidence:", average)

What is total = line + total do

Try this code easy and simpe

fname = input("Enter file name: ")
fhand = open(fname)

total = 0
count = 0

for line in fhand:
if line.startswith("X-DSPAM-Confidence:") :
line = float(line[21:])
total = line + total
count = count + 1

average = total/ count

print("Average spam confidence:", average)

Note: use the file name mbox-short.txt as the file name

SIMPLE AND SHORT

fname = input("Enter file name: ")
fh = open(fname)
total = 0
count = 0
for line in fh:
if line.startswith("X-DSPAM-Confidence:") :
line = float(line[21:])
total = line + total
count = count + 1
average = (total / count)
print("Average spam confidence: " + str(average) )

# Use the file name mbox-short.txt as the file name
fname = input("Enter file name: ")
fh = open(fname)
total = 0
count = 0
for line in fh:
    if not line.startswith("X-DSPAM-Confidence:") : continue
    parts = line.split()
    total = float(parts[1]) + total
    count = count + 1
        

print("Average spam confidence:", total/count)

Use the file name mbox-short.txt as the file name

fname = input("Enter file name: ")
fh = open(fname)
tot = 0
count = 0
for line in fh:
if line.startswith("X-DSPAM-Confidence:"):
count+=1
line = float(line[21:])
tot=tot+line
average = tot/count
print("Average spam confidence:",average)

Use mnemonic variable names and a function.

# Use the file name mbox-short.txt as the file name
def getValue(sLine):
    c = sLine.find(':')
    return float(sLine[c+1:])

fname = input("Enter file name: ")
fh = open(fname)
fSum = 0
nCount = 0

for line in fh:
    if not line.startswith("X-DSPAM-Confidence:") : continue
    fValue = getValue(line)
    fSum = fSum + fValue
    nCount = nCount + 1
    # print ("Each:", fValue, fSum, nCount)

print("Average spam confidence:", fSum/nCount)

fname = input("Enter file name: ")
fh = open(fname)
counter =0
result =0
for line in fh:
if not line.startswith("X-DSPAM-Confidence:") : continue
index = line.find(":")
value = line[index+1:len(line)]
number = value.strip()
float_number =float(number)
result = result + float_number
counter = counter + 1
print("Average spam confidence: {}".format(result/counter))

Easiest answer:
fil = open('C:\Users\admin\OneDrive\Desktop\mbox-short.txt','r')
cnt = 0
a=0
for ch in fil:
if not ch.startswith('X-DSPAM-Confidence:'):
continue
print(ch.rstrip())
cnt+=1
i=ch[20:]
a+=float(i)
print("Average spam Confidence:",a/cnt)

Use the file name mbox-short.txt as the file name

fname = input("Enter file name: ")
fhand = open(fname)

count = 0
for line in fhand:
if line.startswith("X-DSPAM-Confidence:") :
count = count + 1

total = 0
for line in fhand:
if line.startswith("X-DSPAM-Confidence:"):
line = float(line[21:])
total = line + total

average = total/ count

print("Average spam confidence:",average)

In the above code the logic in the line i couldn't got can anyone explain me please?
line = float(line[21:])
total = line + total
how 21 ?