python对象及面向对象技术详解

"""Framework for getting filetype-specific metadata.
Instantiate appropriate class with filename. Returned object acts like a
dictionary, with key-value pairs for each piece of metadata.
  import fileinfo
  info = fileinfo.MP3FileInfo("/music/ap/mahadeva.mp3")
  print "\n".join(["%s=%s" % (k, v) for k, v in info.items()])
Or use listDirectory function to get info on all files in a directory.
  for info in fileinfo.listDirectory("/music/ap/", [".mp3"]):
    ...
Framework can be extended by adding classes for particular file types, e.g.
HTMLFileInfo, MPGFileInfo, DOCFileInfo. Each class is completely responsible for
parsing its files appropriately; see MP3FileInfo for example.
"""
import os
import sys
from UserDict import UserDict
def stripnulls(data):
  "strip whitespace and nulls"
  return data.replace("{post.content}", "").strip()
class FileInfo(UserDict):
  "store file metadata"
  def __init__(self, filename=None):
    UserDict.__init__(self)
    self["name"] = filename
class MP3FileInfo(FileInfo):
  "store ID3v1.0 MP3 tags"
  tagDataMap = {"title"  : ( 3, 33, stripnulls),
         "artist" : ( 33, 63, stripnulls),
         "album"  : ( 63, 93, stripnulls),
         "year"  : ( 93, 97, stripnulls),
         "comment" : ( 97, 126, stripnulls),
         "genre"  : (127, 128, ord)}
  def __parse(self, filename):
    "parse ID3v1.0 tags from MP3 file"
    self.clear()
    try:
      fsock = open(filename, "rb", 0)
      try:
        fsock.seek(-128, 2)
        tagdata = fsock.read(128)
      finally:
        fsock.close()
      if tagdata[:3] == "TAG":
        for tag, (start, end, parseFunc) in self.tagDataMap.items():
          self[tag] = parseFunc(tagdata[start:end])
    except IOError:
      pass
  def __setitem__(self, key, item):
    if key == "name" and item:
      self.__parse(item)
    FileInfo.__setitem__(self, key, item)
def listDirectory(directory, fileExtList):
  "get list of file info objects for files of particular extensions"
  fileList = [os.path.normcase(f)
        for f in os.listdir(directory)]
  fileList = [os.path.join(directory, f)
        for f in fileList
        if os.path.splitext(f)[1] in fileExtList]
  def getFileInfoClass(filename, module=sys.modules[FileInfo.__module__]):
    "get file info class from filename extension"
    subclass = "%sFileInfo" % os.path.splitext(filename)[1].upper()[1:]
    return hasattr(module, subclass) and getattr(module, subclass) or FileInfo
  return [getFileInfoClass(f)(f) for f in fileList]
if __name__ == "__main__":
  for info in listDirectory("/music/_singles/", [".mp3"]):
    print "\n".join(["%s=%s" % (k, v) for k, v in info.items()])
    print

2 使用 from module import 导入模块

我们以前学的导入模块是用下边的语法:

import 模块名

这样在需要使用该模块中的东西时. 要通过 模块名.XXX 的形式. 例如:

>>> import types
>>> types.FunctionType
<type 'function'>
>>> FunctionType

Traceback (most recent call last):
 File "", line 1, in 
NameError: name 'FunctionType' is not defined

>>> from types import FunctionType

>>> FunctionType
<type 'function'>

class A(B) :
  " this is class A. "

__init__

class A(B) :
  "this is class A. "
  def __init__ (self):
    B.__init__(self)

>>> A.__doc__
'this is class A. '
>>> a.__doc__
'this is class A. '

>>> a.__class__
<class __main__.A at 0x011394B0>

class A :
  def __init__(self) :
    self.data = []

>>> class A:
... def __init__(self):
...  self.li = range(5)
... def __getitem__(self, i):
...  return self.li[-i]
...
>>> a = A()
>>> print a[1]

def __setitem__(self, key, item):
  self.li[key] = item

def __repr__(self): return repr(self.li)

repr(a)

def __cmp__(self, x):
  if isinstance(x, A): return cmp(self.li, x.li)

a = A()
b = A()
a == b

def __len__(self): return len(self.li)

def __delitem__(self, key): del self.li[key]

class A :
  l = [1, 2, 3]

A.l

a.__class__.l