Python从fi中提取数据

Question

我正在尝试提取其中包含特定文本文件的文本：

----
data1
data1
data1
extractme
----
data2
data2
data2
----
data3
data3
extractme
----

然后将其转储到文本文件中，以便

----
data1
data1
data1
extractme
---
data3
data3
extractme
---

谢谢你的帮助。

Answer 1

对于Python2

#!/usr/bin/env python

with open("infile.txt") as infile:
    with open("outfile.txt","w") as outfile:
        collector = []
        for line in infile:
            if line.startswith("----"):
                collector = []
            collector.append(line)
            if line.startswith("extractme"):
                for outline in collector:
                    outfile.write(outline)

Python3号

#!/usr/bin/env python3

with open("infile.txt") as infile, open("outfile.txt","w") as outfile:
    collector = []
    for line in infile:
        if line.startswith("----"):
            collector = []
        collector.append(line)
        if line.startswith("extractme"):
            for outline in collector:
                outfile.write(outline)

Answer 2

我认为破折号数量的变化（输入中有4个破折号，输出中有时有4个，有时有3个）是一个错误，并不是实际需要的（因为甚至没有暗示任何算法，以解释在不同情况下要输出多少破折号）。

我将按照阅读和一次生成一段行的方式来组织任务：

def readbyblock(f):
  while True:
      block = []
      for line in f:
          if line = '----\n': break
          block.append(line)
      if not block: break
      yield block

以便（选择性）输出可以与输入整齐地分开：

with open('infile.txt') as fin:
    with open('oufile.txt', 'w') as fou:
        for block in readbyblock(fin):
            if 'extractme\n' in block:
                fou.writelines(block)
                fou.write('----\n')

如果块很大，这就不是最佳性能，因为它在if子句中隐含的块中的所有行上都有一个单独的循环。因此，一个好的重构可能是：

def selectivereadbyblock(f, marker='extractme\n'):
  while True:
      block = []
      extract = False
      for line in f:
          if line = '----\n': break
          block.append(line)
          if line==marker: extract = True
      if not block: break
      if extract: yield block

with open('infile.txt') as fin:
    with open('oufile.txt', 'w') as fou:
        for block in selectivereadbyblock(fin):
            fou.writelines(block)
            fou.write('----\n')

参数化分隔符（对于输入和输出，现在硬编码为“---\n”）是另一个合理的编码调整。

Answer 3

这对我来说足够了。示例数据位于名为“data.txt”的文件中，输出转到“result.txt”

inFile = open("data.txt")
outFile = open("result.txt", "w")
buffer = []
keepCurrentSet = True
for line in inFile:
    buffer.append(line)
    if line.startswith("----"):
        #---- starts a new data set
        if keepCurrentSet:
            outFile.write("".join(buffer))
        #now reset our state
        keepCurrentSet = False
        buffer = []
    elif line.startswith("extractme"):
        keepCurrentSet = True
inFile.close()
outFile.close()