需要在Python中阅读特定范围的文本文件

Question

我需要在特定行之后读取文本文件,例如第100行.此行具有特定数字,例如"255".然后我想用for循环阅读接下来的500行.在那500行我有一些数字要提取.如在P [3]位置.然后我需要将这些值传递给数组.最后我应该有几套如下.我使用以下代码来做到这一点.但我失败了.谁能帮我.

文件如下所示

Generated by trjconv : a bunch of waters t=   0.00000
 500
    1SOL     OW    1   1.5040   2.7580   0.6820
    2SOL     OW    4   1.5210   0.9510   2.2050

  500SOL     OW 2998   1.5310   1.7952   2.1981
   3.12736   3.12736   3.12736
Generated by trjconv : a bunch of waters t= 9000.00000
 500
    1SOL     OW    1   1.5040   2.7580   0.6820
    2SOL     OW    4   1.5210   0.9510   2.2050

  500SOL     OW 2998   1.5310   1.7952   2.1981
   3.10941   3.10941   3.10941
Generated by trjconv : a bunch of waters t=   0.00000
 500
    1SOL     OW    1   1.5040   2.7580   0.6820
    2SOL     OW    4   1.5210   0.9510   2.2050

  500SOL     OW 2998   1.5310   1.7952   2.1981
   3.12736   3.12736   3.12736
Generated by trjconv : a bunch of waters t= 9000.00000
 500
    1SOL     OW    1   1.5040   2.7580   0.6820
    2SOL     OW    4   1.5210   0.9510   2.2050

  500SOL     OW 2998   1.5310   1.7952   2.1981
   3.10941   3.10941   3.10941

编码我写的

F = open('Data.gro', 'r')
A = open('XYZ.txt', 'w')
XO = []
I = range(1,500)
for line in F:
    P = line.split()
    if P[0] == '256': # after i found this I want to read next five hundred lines.
        for R in I:
            P = line.split()
                        XO.append(P[3])
                        R +=1

    # after the for loop I want write 'XO' in to file as set 01 then should go to next P[0] == '256'

结果应如下文件名'XYZ.txt'中的结果

Set 01
X = [1.32, 4.132, 2.23, .... upto 500]
Set 02
X = [4.232, 1.162, 3.73, .... upto 500]

Answer 1

您只需要获取内部循环内的行，您可以使用next()它：

with open('filename') as f:
    for line in f:
       if line.split()[0] == '256':
          for _ in xrange(500):
              line = next(f)
              #do something with line

在上面的代码中，StopIteration如果条件为 True 后文件没有 500 行，您将收到错误，您可以使用 a 来处理该问题，try-except或者使用以下方法获取文件对象的切片itertools.islice：

from itertools import islice
with open('filename') as f:
    for line in f:
       if line.split()[0] == '256':
          XO =[line.split(None, 4)[3] for line in islice(f, 500)]
          #Write XO to a file

如果行不以前导空格开头，那么您可以使用 @zhangxaochen 建议将该line.split()[0] == '256'部分替换为line.startswith('256 '). 另一种选择是使用line.split(None, 1)[0] == '256'，它只会将线分割一次。