##language:zh
'''
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!
'''

-- 218.25.65.133 [<<DateTime(2004-09-30T04:40:07Z)>>]
<<TableOfContents>>
= 描述 =

Computing Directory  Sizes in a Cross-Platform Way

平台无关地计算目录大小

Credit: Frank Fejes



== 问题 Problem ==
You need to compute the total size of a directory (or set of directories) in a way that works under both Windows and Unix-like platforms. 

需要计算目录(或者目录集合)的大小，要求在Windows和类Unix系统上代码都适用。 



== 解决 Solution ==
There are easier platform-dependent solutions, such as Unix's du, but Python also makes it quite feasible to have a cross-platform solution: 

特定平台上有简单的方法，如Unix上的du命令。使用Python可以更容易的获得平台无关的方法：

{{{
#!python
import os
from os.path import *

class DirSizeError(Exception): pass

def dir_size(start, follow_links=0, start_depth=0, max_depth=0, skip_errs=0):

    # Get a list of all names of files and subdirectories in directory start
    try: dir_list = os.listdir(start)
    except:
        # If start is a directory, we probably have permission problems
        if os.path.isdir(start):                                    #译注：没有读权限
            raise DirSizeError('Cannot list directory %s'%start)
        else:  # otherwise, just re-raise the error so that it propagates
            raise

    total = 0L
    for item in dir_list:
        # Get statistics on each item--file and subdirectory--of start
        path = join(start, item)
        try: stats = os.stat(path)
        except: 
            if not skip_errs:
                raise DirSizeError('Cannot stat %s'%path)           #译注：没有读权限
        # The size in bytes is in the seventh item of the stats tuple, so:
        total += stats[6]
        # recursive descent if warranted
        if isdir(path) and (follow_links or not islink(path)):      #译注：遍历计算子目录
            bytes = dir_size(path, follow_links, start_depth+1, max_depth)
            total += bytes
            if max_depth and (start_depth < max_depth):
                print_path(path, bytes)
    return total

def print_path(path, bytes, units='b'):
    if units == 'k':
        print '%-8ld%s' % (bytes / 1024, path)
    elif units == 'm':
        print '%-5ld%s' % (bytes / 1024 / 1024, path)
    else:
        print '%-11ld%s' % (bytes, path)

def usage (name):
    print "usage: %s [-bkLm] [-d depth] directory [directory...]" % name
    print '\t-b\t\tDisplay in Bytes (default)'
    print '\t-k\t\tDisplay in Kilobytes'
    print '\t-m\t\tDisplay in Megabytes'
    print '\t-L\t\tFollow symbolic links (meaningful on Unix only)'
    print '\t-d, --depth\t# of directories down to print (default = 0)'

if _ _name_ _=='_ _main_ _':
    # When used as a script:
    import string, sys, getopt

    units = 'b'
    follow_links = 0
    depth = 0

    try:
        opts, args = getopt.getopt(sys.argv[1:], "bkLmd:", ["depth="])           #译注：解析命令行参数 
    except getopt.GetoptError:
        usage(sys.argv[0])
        sys.exit(1)

    for o, a in opts:
        if o == '-b': units = 'b'
        elif o == '-k': units = 'k'
        elif o == '-L': follow_links = 1
        elif o == '-m': units = 'm'
        elif o in ('-d', '--depth'):
            try: depth = int(a)
            except:
                print "Not a valid integer: (%s)" % a
                usage(sys.argv[0])
                sys.exit(1)

    if len(args) < 1:
        print "No directories specified"
        usage(sys.argv[0])
        sys.exit(1)
    else:
        paths = args

    for path in paths:
        try: bytes = dir_size(path, follow_links, 0, depth)
        except DirSizeError, x: print "Error:", x
        else: print_path(path, bytes)
}}}

== 讨论 Discussion ==

Unix-like platforms have the du command, but that doesn't help when you need to get information about disk-space usage in a cross-platform way. This recipe has been tested under both Windows and Unix, although it is most useful under Windows, where the normal way of getting this information requires using a GUI. In any case, the recipe's code can be used both as a module (in which case you'll normally call only the dir_size function) or as a command-line script. Typical use as a script is: 

类Unix平台上可以使用du命令计算目录大小，但是在其它平台上没有这个命令。上面脚本在Windows和Unix下都测试过。在Windows下面计算目录大小信息通常需要使用GUI(?)，这样脚本在windows下更有用些. 在任何平台下，脚本代码可以作为一个模块(可能仅仅使用dir-size函数)或者作为命令行脚本使用。 典型的使用方法如下：

{{{
C:\> python dir_size.py "c:\Program Files"
}}}

This will give you some idea of where all your disk space has gone. To help you narrow the search, you can, for example, display each subdirectory: 

使用上面命令行脚本可以获得全部磁盘空间的使用情况。如果想获得每个子目录的信息，可以使用'''浅'''搜索:  
{{{
C:\> python dir_size.py --depth=1 "c:\Program Files"
}}}

The recipe's operation is based on recursive descent. os.listdir provides a list of names of all the files and subdirectories of a given directory. If dir_size finds a subdirectory, it calls itself recursively. An alternative architecture might be based on os.path.walk, which handles the recursion on our behalf and just does callbacks to a function we specify, for each subdirectory it visits. However, here we need to be able to control the depth of descent (e.g., to allow the useful --depth command-line option, which turns into the max_depth argument of the dir_size function). This control is easier to attain when we administer the recursion directly, rather than letting os.path.walk handle it on our behalf. 

脚本代码中使用下向递归。os.listdir获得指定目录下所有文件名称和子目录名称的list。如果函数dir_size判断出一个子目录，会递归调用自己。另一种解决方法是以os.path.walk为基础，walk代替我们处理递归，在每个子目录上使用我们指定的回调函数获得目录大小信息。不过，这里我们需要控制递归的深度(比如，允许使用便利的命令行参数--depth来确定dir_size函数的参数max_depth)，直接处理递归而不用os.path.walk代替我们处理， 可以更容易的控制函数行为。  


== 参考 See Also ==

Documentation for the os.path and getopt modules in the Library Reference.