描述

统计文件行数

问题 Problem

需要计算文件的行数

解决 Solution

The simplest approach, for reasonably sized files, is to read the file as a list of lines so that the count of lines is the length of the list.

对于具有适当大小的文件，最简单方法是拷贝文件各行到一个list中，list的长度就是文件的行数。

If the file's path is in a string bound to the thefilepath variable, that's just:

如果文件路径由下面的string变量thefilepath给出，代码如下：

count = len(open(thefilepath).readlines(  ))

For a truly huge file, this may be very slow or even fail to work. If you have to worry about humongous files, a loop using the xreadlines method always works:

对于很大的文件，readlines可能很慢，甚至操作失败。如果需要处理特别巨大的文件，使用xreadlines函数的循环可以保证不会出问题：

count = 0
for line in open(thefilepath).xreadlines(  ): count += 1

Here's a slightly tricky alternative, if the line terminator is '\n' (or has '\n' as a substring, as happens on Windows):

如果行分隔符号是'\n' (Windows中'\n'作为一个子串出现)，那么可以选用如下的小技巧：

count = 0
thefile = open(thefilepath, 'rb')
while 1:
    buffer = thefile.read(8192*1024)  
    if not buffer: break
    count += buffer.count('\n')                         #string函数count 
thefile.close(  )

Without the 'rb' argument to open, this will work anywhere, but performance may suffer greatly on Windows or Macintosh platforms.

如果不使用上面的rb参数，脚本也会正常工作，但是在Windows或Macintosh平台上可能有很大的效率损失。

讨论 Discussion

If you have an external program that counts a file's lines, such as wc -l on Unix-like platforms, you can of course choose to use that (e.g., via os.popen( )). However, it's generally simpler, faster, and more portable to do the line-counting in your program. You can rely on almost all text files having a reasonable size, so that reading the whole file into memory at once is feasible. For all such normal files, the len of the result of readlines gives you the count of lines in the simplest way. 如果可以使用外部程序，比如类Unix平台上命令 wc -l来统计文件行数，那么应该使用这个程序(在脚本中利用 os.popen()). 但更简单快捷, 具有移植性的做法是在程序中编码计算文件行数。可以认为几乎所有的文本文件具有合适的大小，一次读入内存处理是适当的。对这种文件，readlines读出的序列长度最简单地给出了文件行数。

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PyCkBk-4-7

描述

问题 Problem

解决 Solution

讨论 Discussion

参考 See Also