从txt文件的多行中提取特定值

Question

以前也有人问过和回答过类似的问题，但我想知道为什么我的代码不能产生正确的输出。

在我的txt文件中有几行代码如下：X-DSPAM-Confidence: 0.xxxx

0.xxxx值会有所不同。我需要从每个“X-DSPAM-置信度：”行中切出这一部分，并计算平均值。

可在此处下载txt文件：http://www.py4e.com/code3/mbox-short.txt

我的代码如下：

fname = input("Enter file name: ")
fh = open(fname)
count = 0
current = 0
for line in fh:
    if not line.startswith("X-DSPAM-Confidence:") : continue   # Please do not change this line and develop the program based on it
    count = count + 1  # I think this would count how many lines that starts with X-DSPAM-Confidence:
    pos = line.find(':')    # This should find me the position for ":"
    number = line[pos+5:]   # I think this should slice the number out
    final = float(number) + current    # Then I float the number and add to the current running number
print("Average spam confidence: ", final/count)    # Finally, when the loop finishes with the file, print the average

使用上面的代码，我得到了平均33.5925925926，但正确的答案应该是0.750718518519。

有没有人能开导一下我？

Answer 1

按照您的要求，只需进行最少但必要的更改。

    fname = input("Enter file name: ")
    with open(fname, "r") as current_file: 
        # i can not stress enough the importance of the with method over 
        #open()/close()
            content = current_file.readlines()

    count = 0
    current = 0
    for line in content:
        if not line.startswith("X-DSPAM-Confidence:"): continue
        count = count + 1  
        pos = line.find(':')    
        number = line[pos+2:]   # small error, it was not 5 but 2 instead
        current = float(number) + current
    print("Average spam confidence: ", current/count)