用python计算平均值

Question

Am正在编写一个提示输入文件名的程序，然后打开该文件并读取该文件，以查找以下形式的行：

X-DSPAM-置信度：0.8475

我想对这些行进行计数，并从每行中提取浮点值，然后计算这些值的平均值。 请给我一些帮助。 我刚刚开始编程，所以我需要一些简单的东西。 这是我已经编写的代码。

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

遍历文件（使用上下文管理器（“ with”）自动处理关闭），查找此类行（就像您所做的那样），然后像这样读取它们：

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)

或更紧凑：

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

尝试：

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

这样total / count为您提供答案。

Answer 3

如下所示的程序应该可以满足您的需求。 如果您需要更改程序寻找的内容，只需更改PATTERN变量以描述您要匹配的内容。 该代码是为Python 3.x编写的，但如果需要，可以很容易地适用于Python2.x。

程序：

#! /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))

---

如果需要，您还可以按照以下方式实现get_numbers生成器。

替代方案：

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))