来自输出变量的Python搜索字符串，并打印下两条线

Question

如何从命令输出中搜索字符串，并从输出中打印下两行。

以下是代码：

a = """
Some lines I do not want 
----- -------- --
I need this line
I need this line also
Again few lines i do not want
"""
for line in a.split("n"):
    if line.startswith("----"):
        print "I need this line"
        print "I need this line also"

我在上面的代码中所做的是，我正在检查行是否以" ---"开头，这可以正常工作。现在，如何在行以" ---"开头后精确打印两行。在此示例代码打印中："我需要这条线，我还需要此行"

Answer 1

您可以从列表中创建一个迭代器(文件句柄无需使用btw(。然后让for迭代，但允许在循环中手动使用next：

a = """
Some lines I do not want
----- -------- --
I need this line
I need this line also
Again few lines i do not want
"""
my_iter = iter(a.splitlines())
for line in my_iter:
    if line.startswith("----"):
        print(next(my_iter))
        print(next(my_iter))

如果破折号之后没有足够的线路，则此代码将升高StopIteration。避免此问题的一种替代方法是(礼貌乔恩·克莱门茨(

from itertools import islice
my_iter = iter(a.splitlines(True))  # preserves n (like file handle would do)
for line in my_iter:
    if line.startswith("----"):
        print(''.join(islice(my_iter, 2)))

另一种方式，不拆分字符串：

print(re.search("-----.*n(.*n.*)",a).group(1))

这将在 unsplitted ，多行字符串中的模式之后搜索2行。如果re.search返回None，可能会崩溃

在这两种情况下，您都会得到：

I need this line
I need this line also

Answer 2

这是一种简单的方法：

a = """
Some lines I do not want 
----- -------- --
I need this line
I need this line also
Again few lines i do not want
"""
lines = a.split("n")
for i in range(len(lines)):
    if lines[i].startswith("----"):  # if current line starts with ----
        print(lines[i+1])  # print next line.
        print(lines[i+2])  # print line following next line.
# I need this line
# I need this line also                                      

Answer 3

您可以存储当前行的索引，从而获取下一个n行：

a = """
Some lines I do not want 
----- -------- --
I need this line
I need this line also
Again few lines i do not want
"""
lines = a.split("n")
for index, line in enumerate(lines):
    if line.startswith("----"):
        print lines[index+1]
        print lines[index+2]

您可能需要检查IndexErrorS。

Answer 4

平原方式(几乎c(：

>>> a = """
Some lines I do not want
----- -------- --
I need this line
I need this line also
Again few lines i do not want
No nee
---- ------- --
Need this
And this
But Not this
"""
>>> start_printing, lines_printed = False, 0
>>> for line in a.split('n'):
        if line.startswith('----'):
            start_printing = True
        elif start_printing:
            print line
            lines_printed += 1
        if lines_printed>=2:
            start_printing=False
            lines_printed = 0

I need this line
I need this line also
Need this
And this

Answer 5

在这里列表综合的东西：

    a = """
    Some lines I do not want 
    ----- -------- --
    I need this line
    I need this line also
    -----------------------
    A line after (---)
    A consecutive line after (---)
    """
   lines = a.split("n")
   test = [print(lines[index+1] + 'n' + lines[index+2]) for index in range(len(lines)) if lines[index].startswith("----")]
 #Output:I need this line
         #I need this line also
         #A line after (---)
         #A consecutive line after (---)

我在进一步测试中碰到IndexError，并增加了更多句子，因此我添加了一个例外块：

a = """
Some lines I do not want 
----- -------- --
I need this line
I need this line also
-----------------------
A line after (---)
A consecutive line after (---)
-------------------------
Just for fun
Another one
-------------------------
"""
lines = a.split("n")
try:
    test = [print(lines[index+1] + 'n' + lines[index+2]) for index in range(len(lines)) if lines[index].startswith("----")]
except:
    pass

现在，所需的输出毫无例外：

I need this line
I need this line also
A line after (---)
A consecutive line after (---)
Just for fun
Another one