Python parsing through a line using for loop?

Question

Write a program to prompt for a file name, and then read through the file and look for lines of the form: X-DSPAM-Confidence: 0.8475 When you encounter a line that starts with “X-DSPAM-Confidence:” pull apart the line to extract the floating point number on the line. Count these lines and the compute the total of the spam confidence values from these lines. When you reach the end of the file, print out the average spam confidence.

Enter the file name: mbox.txt
Average spam confidence: 0.894128046745

Enter the file name: mbox-short.txt
Average spam confidence: 0.750718518519 Test your file on the mbox.txt and mbox-short.txt files.

So far I have:

 fname = raw_input("Enter file name: ")
 fh = open(fname)
 for line in fh:
     pos  = fh.find(':0.750718518519')
     x = float(fh[pos:])
     print x

What is wrong with this code?

Alex L · Accepted Answer · 2013-01-24 06:29:20Z

4

It sounds like they're asking you to average all the 'X-DSPAM-Confidence' numbers, rather than find 0.750718518519.

Personally, I'd find the word you're looking for, extract the number, then put all these numbers into a list and average them at the end.

Something like this -

# Get the filename from the user
filename = raw_input("Enter file name: ")

# An empty list to contain all our floats
spamflts = []

# Open the file to read ('r'), and loop through each line
for line in open(filename, 'r'):

    # If the line starts with the text we want (with all whitespace stripped)
    if line.strip().startswith('X-DSPAM-Confidence'):

        # Then extract the number from the second half of the line
        # "text:number".split(':') will give you ['text', 'number']
        # So you use [1] to get the second half
        # Then we use .strip() to remove whitespace, and convert to a float
        flt = float(line.split(':')[1].strip())

        print flt

        # We then add the number to our list
        spamflts.append(flt)

print spamflts
# At the end of the loop, we work out the average - the sum divided by the length
average = sum(spamflts)/len(spamflts)

print average

>>> lines = """X-DSPAM-Confidence: 1
X-DSPAM-Confidence: 5
Nothing on this line
X-DSPAM-Confidence: 4"""

>>> for line in lines.splitlines():
    print line


X-DSPAM-Confidence: 1
X-DSPAM-Confidence: 5
Nothing on this line
X-DSPAM-Confidence: 4

Using find:

>>> for line in lines.splitlines():
    pos = line.find('X-DSPAM-Confidence:')
    print pos

0
0
-1
0

We can see that find() just gives us the position of 'X-DSPAM-Confidence:' in each line, not the position of the number after it.

It's easier to find if a line starts with 'X-DSPAM-Confidence:', then extract just the number like this:

>>> for line in lines.splitlines():
    print line.startswith('X-DSPAM-Confidence')


True
True
False
True

>>> for line in lines.splitlines():
    if line.startswith('X-DSPAM-Confidence'):
        print line.split(':')


['X-DSPAM-Confidence', ' 1']
['X-DSPAM-Confidence', ' 5']
['X-DSPAM-Confidence', ' 4']

>>> for line in lines.splitlines():
    if line.startswith('X-DSPAM-Confidence'):
        print float(line.split(':')[1])


1.0
5.0
4.0

edited Jan 24, 2013 at 6:29

answered Jan 24, 2013 at 5:55

Alex L

9,0136 gold badges53 silver badges77 bronze badges

Sign up to request clarification or add additional context in comments.

14 Comments

Joran Beasley Over a year ago

heh you just did his assignment for him practically :P (still +1 for giving a right answer)

Alex L Over a year ago

@JoranBeasley Yeah, I guess so. It's probably not the best way to learn, but hopefully he'll read through and try and understand it. (There's no homework tag any more is there?)

Alex L Over a year ago

@JoranBeasley I've added a few comments that should help him understand it

user2006018 Over a year ago

still a little confused i dont believe spamflts is defined anywhere?

user2006018 Over a year ago

however if I wanted to prompt the user to enter the file without declaring an array how would i do it? or can i do it like this: x = raw_input("File name:") and then spamflts [] = x

|

Joran Beasley · Accepted Answer · 2013-01-24 06:06:18Z

-1

line.find #..... so you search the line ....

print pos #prints help with debugging ;)

float(fh[pos+1:]) #the index you got is actually the : so you need to move over 1 more

edited Jan 24, 2013 at 6:06

answered Jan 24, 2013 at 5:55

Joran Beasley

114k13 gold badges168 silver badges187 bronze badges

Collectives™ on Stack Overflow

Python parsing through a line using for loop?

2 Answers 2

14 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

14 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related