Question

我试图遍历一堆文本文件，并将每个文件的第二行附加到列表中。以下是我的示例代码。看起来应该很接近了，但是什么都没有添加到我的列表中。

import os
directory = 'C:\\my_path\\'
i=0
list2 = []
for filename in os.listdir(directory):
    with open(directory + filename) as infile:
        try:
            print(filename)
            i=i+1
            print(i)
            data = infile.readlines()
            for line in data:
                if (line == 2):
                    list2.append(line)
                    infile.close()
        except:
            print(filename + ' is throwing an error')
print('DONE!!')
print(list2)

Answer 1

写作时：

for line in data:
    if (line == 2):
        list2.append(line)
        infile.close()

line变量不是行的索引，而是行本身作为字符串。

还要注意，第二行的索引为1，而不是2，因为索引在Python中从0开始。

您至少应将此循环更改为：

for index, line in enumerate(data):
    if (index == 1):
        list2.append(line)
        infile.close()

此外，正如@ bruno-desthuilliers所建议的那样，您不需要使用占用内存的readlines()方法，而是可以像这样直接在文件上进行迭代：

#no infile.readlines() needed
for index, line in enumerate(infile):
    if (index == 1):
        list2.append(line)
        infile.close()

最后，在将语句包装在infile.close()块中时，不需要调用with。通话已为您完成。

Answer 2

当您测试Subscribe时，是否在询问您从line == 2读取的行是否等于infile（从来没有）。相反，您需要一些计数器来测试您是否在第2行。甚至更好的是，只需对其进行索引：

Answer 3

您的代码中的

line == 2试图将文本/字符串与数字2进行比较，这无助于捕获正在读取的行的序数。

相反，只需跳过第一行并将下一行附加到结果列表中即可。

注意：

如果您只需要第二行，则无需阅读所有行infile.readlines()！
使用上下文管理器close时不需要with ...文件处理程序

import os

directory = 'C:\\my_path\\'
list2 = []
for filename in os.listdir(directory):
    with open(directory + filename) as infile:
        try:
            print(filename)
            next(infile)
            list2.append(next(infile))
        except:
            print(filename + ' is throwing an error')
print('DONE!!!')
print(list2)

Answer 4

尝试此版本：

import os
directory = 'C:\\my_path\\'

secondLines = []

for filename in os.listdir(directory):
    try:
        #Use open() because it is optimized and does not read the whole file into RAM
        with open(directory + "\\" + filename) as infile:
            for lineIndex, line in enumerate(infile):
                if lineIndex == 1:
                    secondLines.append(line)
    except:
        print(filename + ' is throwing an error')

print(secondLines)

您的版本：

import os
directory = 'C:\\my_path\\'
i=0
list2 = []
for filename in os.listdir(directory):
    #add "\\" to read the correct file
    with open(directory + "\\" + filename) as infile:
        try:
            print(filename)
            i=i+1
            print(i)
            data = infile.readlines()  
            #To get the second line, you have to use indexes
            for line in range(len(data)):
                #if line (index) equals 1, it is the second line (0th element is first)
                if (line == 1):
                    #If the index of the line is 1, append it to the list
                    #data[line] = take the element on index 1 from list data. Indexing starts at 0
                    list2.append(data[line])
                    infile.close()
        except:
            print(filename + ' is throwing an error')
print('DONE!!')
print(list2)

Answer 5

接下来是另一种优雅的实现方式，该方式可以避免迭代所有数据以及自动打开和关闭文件。

# With open should take care of automatic opening and closing of file. You don't need to close it explicitly. 
 with open(directory + filename) as infile:
        try:
            print(filename)
            i=i+1
            print(i)
            skip_count = 0
            line in infile:
                 skip_count += 1
                 if skip_count == 2:
                    list2.append(line)
                    break # This will go out of loop and you don't have to iterate through all the data
        except:
            print(filename + ' is throwing an error')

尝试遍历多个文本文件并将第二行附加到列表中

5 个答案: