6.7. Summary
The fileinfo.py program introduced
in Chapter
5 should now make perfect sense.
第五章介绍的fileinfo程序现在应该都讲得通了。
- """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("\00", "").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
Before diving into the next chapter, make sure you're
comfortable doing the following things:
在深入下一章之前,确定你已经掌握了下面的知识点:
- Catching
exceptions with try...except
- Protecting
external resources with try...finally
- Reading
from files
- Assigning
multiple values at once in a for loop
- Using
the os module
for all your cross-platform file manipulation needs
- Dynamically instantiating classes
of unknown type by treating classes as
objects and passing them around
- 使用try…except捕捉异常
- 使用try..finally保护外部资源
- 读取文件
- 在for循环一次进行多个变量赋值
- 根据你跨平台进行操作的需要,使用os模块
- 通过将类视作对并用它进行传值来动态的实例化一个未知类
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