无法使用readlines（）索引同时读取两行超出范围

Question

我有一些文本文件包含7行当我试图打印第3行和第4行使用以下代码，它打印第3行，然后给我一个索引超出范围的错误

for root, subFolders, files in os.walk(folder):
    for file in files:
        if file.endswith('Init.txt'):
            with open(os.path.join(root, file), 'r') as fRead:
                line_3 = fRead.readlines()[3]
                line_4 = fRead.readlines()[4]
                print line_3
                print line_4

但是，当我运行以下任何一个代码时，我没有得到任何错误

代码1:第3行打印正确

for root, subFolders, files in os.walk(folder):
    for file in files:
        if file.endswith('Init.txt'):
            with open(os.path.join(root, file), 'r') as fRead:
                line_3 = fRead.readlines()[3]
                print line_3

代码2:第4行打印正确

for root, subFolders, files in os.walk(folder):
    for file in files:
        if file.endswith('Init.txt'):
            with open(os.path.join(root, file), 'r') as fRead:
                line_4 = fRead.readlines()[4]
                print line_4

好像我不能同时读两行字。这太令人沮丧了

Answer 1

方法readlines()读取文件中的所有行，直到到达EOF（文件结尾）。 “cursor”位于文件的末尾，随后对readlines()的调用不会产生任何结果，因为EOF是直接找到的

因此，在line_3 = fRead.readlines()[3]之后，您已经使用了整个文件，但只存储了第四个（！）文件的行（如果您从1开始计算行数）

如果你这样做了

all_lines =  fRead.readlines()
line_3 = all_lines[3]
line_4 = all_lines[4]

您只读取了一次文件并保存了所需的所有信息

Answer 2

如文件所述：

Help on built-in function readlines:

readlines(hint=-1, /) method of _io.TextIOWrapper instance Return a list of lines from the stream.

hint can be specified to control the number of lines read: no more
lines will be read if the total size (in bytes/characters) of all
lines so far exceeds hint.

用完所有行后，对readlines的下一个调用将为空

更改函数以将结果存储在临时变量中：

with open(os.path.join(root, file)) as fRead:
    lines = fRead.readlines()
    line_3 = lines[3]
    line_4 = lines[4]
    print line_3
    print line_4