[英]Read between lines in text file
首先,我的示例文本文件的内容如下所示:
Some Data
Nothing important
Start here
This is important
Grab this line too
And this ono too
End here
Text goes on, but isn't important
Next text
Blaah
现在,我想读入文本文件,并且只想在“ 从这里开始 ”和“ 从这里 结束 ”之间抓线。
所以我的Python代码看起来像:
filename = 'example_file.txt'
with open(filename, 'r') as input:
for line in input: # First loop breaks at specific line
if 'Start here' in line:
break
for line_1 in input: # Second loop grabs all lines
print line_1.strip()
for line_2 in input: # Third loop breaks at specific line
if 'End here' in line_2:
break
但这是行不通的。
这是我运行时的输出:
This is important
Grab this line too
And this on too
End here
Text goes on, but isn't important
Next text
Blaah
如您所见,我的脚本没有在End here中断。 程序从正确的行开始,但没有在正确的行中断。
怎么了?
这是需要休息的第二个循环...
for line_1 in input:
if 'End here' in line_1:
break
print line_1.strip()
您的问题是您应该在第二个循环中检查“ End Here”,因为第二个和第三个循环不会同时运行。 实际上,第三个循环甚至不会运行。
考虑到这一点,此代码将起作用:
filename = 'mydata.txt'
with open(filename, 'r') as f:
for line in f:
if 'Start here' in line:
break
for line_1 in f:
if 'End here' in line:
break
else:
print line.strip()
但是,我们仍然可以进行一些优化:
break
后的任何代码都不会运行,因此我们可以摆脱else
; open
默认情况下使用读取模式。 考虑到这一点,您的最终代码将如下所示:
filename = 'mydata.txt'
with open(filename) as f:
for line in f:
if 'Start here' in line:
break
for line in f:
if 'End here' in line:
break
print line.strip()
运行它,您将获得所需的输出:
This is important
Grab this line too
And this ono too
您可以使用带有re.DOTALL
选项的正则表达式( re
模块),以便将换行符视为正则字符。
import re
source = """Some Data
Nothing important
Start here
This is important
Grab this line too
And this ono too
End here
Text goes on, but isn't important
Next text
Blaah"""
# or else:
# source = open(filename, 'r').read() # or similar
result = re.search("Start here(.*)End here", source, re.DOTALL).group(1).strip()
print result
> This is important
> Grab this line too
> And this ono too
工作原理:
re.search
在某些字符串中寻找模式; .*
表示“任何字符,任何次数”。 需要在两个硬编码的标记之间进行所有操作(即Start Here
和End here
); re.DOTALL
是个秘密:它将换行符视为常规字符串字符。 点是“任何字符”的符号,因此“全部点”的意思是“将任何字符作为常规字符,甚至换行字符进行处理”。 group(1)
表示您想要第二个(从零开始的索引)组,它是括号内的组。 您可以先阅读所有行并进行枚举:
filename = 'example_file.txt'
useful_content = []
with open(filename, 'r') as input:
all_lines = input.readlines() # read all lines
for idx in range(len(all_lines)): # iterate all lines
if 'Start here' in all_lines[idx]:
useful_content.append(all_lines[idx].strip())
idx = idx + 1
# found start of useful contents, continue iterate till it ends
while 'End here' not in all_lines[idx]:
useful_content.append(all_lines[idx].strip())
idx = idx + 1
break
for line in useful_content:
print(line)
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.