8. Python自定义模块humansize

我们在提取一个文件元信息的时候，经常会使用到获取元信息的size， 但是默认提取出来的是字节为单位计算的大小，我们需要转换成MB或者GB 或者TB的大小。

因此就需要使用到humansize这个模块， 这个模块不是系统内置的， 你可以通过help（）查询内置模块是没有这个的模块的。 需要从其他地方导入才可以进行使用。

将下面的文件保存成humansize.py 放在默认python目录下。

 '''''Convert file sizes to human-readable form. 

 Available functions:
 approximate_size(size, a_kilobyte_is_1024_bytes)
     takes a file size and returns a human-readable string 

 Examples:
 >>> approximate_size(1024)
 '1.0 KiB'
 >>> approximate_size(1000, False)
 '1.0 KB' 

 '''  

 SUFFIXES = {1000: ['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'],
             1024: ['KiB', 'MiB', 'GiB', 'TiB', 'PiB', 'EiB', 'ZiB', 'YiB']}  

 def approximate_size(size, a_kilobyte_is_1024_bytes=True):
     '''''Convert a file size to human-readable form. 

     Keyword arguments:
     size -- file size in bytes
     a_kilobyte_is_1024_bytes -- if True (default), use multiples of 1024
                                 if False, use multiples of 1000 

     Returns: string 

     '''
     if size < 0:
         raise ValueError('number must be non-negative')  

     multiple = 1024 if a_kilobyte_is_1024_bytes else 1000
     for suffix in SUFFIXES[multiple]:
         size /= multiple
         if size < multiple:
             return '{0:.1f} {1}'.format(size, suffix)  

     raise ValueError('number too large')  

 if __name__ == '__main__':
     print(approximate_size(1000000000000, False))
     print(approximate_size(1000000000000))  

 # Copyright (c) 2009, Mark Pilgrim, All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without modification,
 # are permitted provided that the following conditions are met:
 #
 # * Redistributions of source code must retain the above copyright notice,
 #   this list of conditions and the following disclaimer.
 # * Redistributions in binary form must reproduce the above copyright notice,
 #   this list of conditions and the following disclaimer in the documentation
 #   and/or other materials provided with the distribution.
 #
 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 'AS IS'
 # AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 # ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 # LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 # CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 # SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 # INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 # CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE. 

 该程序的功能是将以字节为单位的文件大小转换为以更易读形式，如将1024 B转换为1KB

 >>> import sys
 >>> import os
 >>> metadata = os.stat('test.docx')
 >>> metadata
 nt.stat_result(st_mode=33206, st_ino=0L, st_dev=0L, st_nlink=0, st_uid=0, st_gid=0, st_size=4934265L, st_atime=1472518662L, st_mtime=1469435178L, st_ctime=1472518662L)
 >>> metadata.st_size
 4934265L
 >>> import humansize
 >>> humansize.approximate_size(metadata.st_size )
 '4.0 MiB'
 >>>