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| 使用标准模块'''linecache'''处理，手到擒来！ | 使用标准模块'''linecache'''处理，很简单： |
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| The standard linecache module is usually the optimal Python solution for this task, particularly if you have to do this repeatedly for several of a file's lines, as it caches the information it needs to avoid uselessly repeating work. Just remember to use the module's clearcache function to free up the memory used for the cache, if you won't be getting any more lines from the cache for a while but your program keeps running. You can also use checkcache if the file may have changed on disk and you require the updated version. | |
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| 使用标准模块'''linecache'''处理这个任务，一般来说是最佳方法。由于lincecache缓存了文件(行?)的信息，当需要多次提取文件的某些特定行时，可以避免无用的重复操作。 | 使用标准模块'''linecache'''处理这个任务，一般来说是最佳方法。由于lincecache缓存了文件的信息，当需要多次提取文件的某些特定行时，可以避免无用的重复操作。 |
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| 如果硬盘上文件有了变化，可以使 | 使用'''checkcache'''方法可以检查磁盘文件是否已经变化，如果变化可以更新缓存信息。 |
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| '''linecache'''读取并缓存作为参数传入的文件的全部信息。如果处理一个很大的文件，而且只需要读取某一个特定行，使用'''linecache'''可能会进行不是严格必须的操作。如果这个例程恰好是程序性能瓶颈，可以使用显示 reads and caches all of the text file whose name you pass to it, so if it's a very large file and you need only one of its lines, linecache may be doing more work than is strictly necessary. Should this happen to be a bottleneck for your program, you may get some speed-up by coding an explicit loop, encapsulated within a function. Here's how to do this in Python 2.2: def getline(thefilepath, desired_line_number): if desired_line_number < 1: return '' current_line_number = 0 for line in open(thefilepath): current_line_number += 1 if current_line_number == desired_line_number: return line return '' |
文章来自《Python cookbook》. 翻译仅仅是为了个人学习,其它商业版权纠纷与此无关!
-- 61.182.251.99 [DateTime(2004-09-20T22:17:38Z)] TableOfContents
描述
读取文件特定行
问题 Problem
读取文件的指定一行
4.5.2 Solution
解决 Solution
The standard linecache module makes this a snap:
使用标准模块linecache处理，很简单：
import linecache theline = linecache.getline(thefilepath, desired_line_number)
讨论 Discussion
使用标准模块linecache处理这个任务，一般来说是最佳方法。由于lincecache缓存了文件的信息，当需要多次提取文件的某些特定行时，可以避免无用的重复操作。
如果不再需要读取文件特定行而且脚本需要继续运行，应该使用linecache的clearcache方法释放缓存占用的内存。
使用checkcache方法可以检查磁盘文件是否已经变化，如果变化可以更新缓存信息。
linecache读取并缓存作为参数传入的文件的全部信息。如果处理一个很大的文件，而且只需要读取某一个特定行，使用linecache可能会进行不是严格必须的操作。如果这个例程恰好是程序性能瓶颈，可以使用显示 reads and caches all of the text file whose name you pass to it, so if it's a very large file and you need only one of its lines, linecache may be doing more work than is strictly necessary. Should this happen to be a bottleneck for your program, you may get some speed-up by coding an explicit loop, encapsulated within a function. Here's how to do this in Python 2.2:
def getline(thefilepath, desired_line_number):
if desired_line_number < 1: return current_line_number = 0 for line in open(thefilepath):
- current_line_number += 1 if current_line_number == desired_line_number: return line
return
...