用python计算平均值

Question

Am Writing 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

I want to count these lines and extract the floating point values from each of the lines and compute the average of those values. Can I please get some help. I just started programming so I need something very simple. This is the code I have already written.

fname = raw_input("Enter file name: ")
    if len(fname) == 0:
        fname = 'mbox-short.txt'
    fh = open(fname,'r')
    count = 0
    total = 0
    #Average = total/num of lines
    for line in fh:
        if not line.startswith("X-DSPAM-Confidence:"): continue
        count = count+1
        print line

Answer 1

Iterate over the file (using the context manager ("with") handles the closing automatically), looking for such lines (like you did), and then read them in like this:

fname = raw_input("Enter file name:")
if not fname:
    fname = "mbox-short.txt"
scores = []
with open(fname) as f:
    for line in f:
        if not line.startswith("X-DSPAM-Confidence:"):
            continue
        _, score = line.split()
        scores.append(float(score))
print sum(scores)/len(scores)

Or a bit more compact:

mean = lambda x: sum(x)/len(x)
with open(fname) as f:
    result = mean([float(l.split()[1]) if line.startswith("X-DSPAM-Confidence:") for l in f])

Answer 2

Try:

total += float(line.split(' ')[1])

so that total / count gives you the answer.

Answer 3

A program like the following should satisfy your needs. If you need to change what the program is looking for, just change the PATTERN variable to describe what you are trying to match. The code is written for Python 3.x but can be adapted for Python 2.x without much difficulty if needed.

Program:

#! /usr/bin/env python3
import re
import statistics
import sys


PATTERN = r'X-DSPAM-Confidence:\s*(?P<float>[+-]?\d*\.\d+)'


def main(argv):
    """Calculate the average X-DSPAM-Confidence from a file."""
    filename = argv[1] if len(argv) > 1 else input('Filename: ')
    if filename in {'', 'default'}:
        filename = 'mbox-short.txt'
    print('Average:', statistics.mean(get_numbers(filename)))
    return 0


def get_numbers(filename):
    """Extract all X-DSPAM-Confidence values from the named file."""
    with open(filename) as file:
        for line in file:
            for match in re.finditer(PATTERN, line, re.IGNORECASE):
                yield float(match.groupdict()['float'])


if __name__ == '__main__':
    sys.exit(main(sys.argv))

---

You may also implement the get_numbers generator in the following way if desired.

Alternative:

def get_numbers(filename):
    """Extract all X-DSPAM-Confidence values from the named file."""
    with open(filename) as file:
        yield from (float(match.groupdict()['float'])
                    for line in file
                    for match in re.finditer(PATTERN, line, re.IGNORECASE))