[python] classes help
Author
Does anyone know any good articles on classes and OOP for python?
I've read about classes in 3 different books (byte of python, thinkCS, and dive into python)
thinkCS barely covers them along with byte but when I read about them in dive it went through alot about them and I was COMPLETELY lost for the most part
I get really confused when it comes to working between ascendants and descendants and when to use self, how to call things between them etc
thanks
Is it that you get confused on the syntax that Python uses? You understand and can use OOP designs, you just have trouble with using Python and OOP together.
Or do you have trouble with OOP itself? You see the syntax, but it's like hitting a wall, or having everything go through your head? That is, you understand the syntax, but cannot fathom how you might possibly use it in any code you write?
Or do you have trouble with OOP itself? You see the syntax, but it's like hitting a wall, or having everything go through your head? That is, you understand the syntax, but cannot fathom how you might possibly use it in any code you write?
Author
I think i'm having trouble understanding some of the the syntax and rules not OOP itself ( i don't even know if that makes sense O.o) when it gets into using classes within classes and some of the more advanced things
this is the code the chapter goes through explaining:
edit: the site doesn't keep the indents so I guess it's not easy to follow on here
[Edited by - revisioned on July 25, 2008 12:14:45 AM]
this is the code the chapter goes through explaining:
[source lang=python] """Framework for getting filetype−specific metadata.Instantiate appropriate class with filename. Returned object acts like adictionary, with key−value pairs for each piece of metadata.import fileinfoinfo = 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 forparsing its files appropriately; see MP3FileInfo for example."""import osimport sysfrom UserDict import UserDictdef 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"] = filenameclass 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:Dive Into Python 47fsock = 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:passdef __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 fileListif 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 FileInforeturn [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()])printTedit: the site doesn't keep the indents so I guess it's not easy to follow on here
[Edited by - revisioned on July 25, 2008 12:14:45 AM]
Python RELIES on proper indentation, so that code you posted only MAY be readable. But, regardless, I won't bother because I never got deep enough into Python to solve your problem.
Put source lang="python" (in square brackets [] ) before your code, /source after, and repost.
Put source lang="python" (in square brackets [] ) before your code, /source after, and repost.
Quote:Original post by revisioned
this is the code the chapter goes through explaining:
"""Framework for getting filetype−specific metadata.Instantiate appropriate class with filename. Returned object acts like adictionary, with key−value pairs for each piece of metadata.import fileinfoinfo = 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 forparsing its files appropriately; see MP3FileInfo for example."""import osimport sysfrom UserDict import UserDictdef 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"] = filenameclass 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: Dive Into Python 47 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".See how much more readable that is? [smile]
Quote:like for instance the book says things like __setitem__ and __parse are special attributes so why is he defining them?
They are special attributes in that their presence enables your class to access specific functionality. For instance, implementing __setitem__ allows your class instances to behave like a writeable dictionary.
Quote:also I don't understand how everything works together and runs from this:if __name__ == "__main__": for info in listDirectory("/music/_singles/", [".mp3"]): print "\n".
First of all, that code is probably wrong. It will simply print a blank newline for each element in the list. Secondly, every module in Python, including the currently executing one, has a name. You can access (read) that name by checking the __name__ property. The module invokved from the shell, etc, is named"__main__". You can check if your script is being executed from the command line this way, and - for example - cause your module to perform special validation steps in that case.
Author
The book won't copy the indents so I did a screenshot:
http://img74.imageshack.us/img74/2461/part1li2.jpg
http://img401.imageshack.us/img401/2884/part2wj1.jpg
it's 2 parts
Edit:
so the book's code is wrong?
also I already know about the __main__ and __name__ things
http://img74.imageshack.us/img74/2461/part1li2.jpg
http://img401.imageshack.us/img401/2884/part2wj1.jpg
it's 2 parts
Edit:
so the book's code is wrong?
also I already know about the __main__ and __name__ things
Quote:Original post by revisioned
so the book's code is wrong?
That's not what I said.
listDirectory() is a function that is not a part of a class. It calls a method to do the heavy lifting.
Oluseyi's correction retained some of the other pasting errors.
The actual code is online here: Chapter 5. Objects and Object-Orientation
You still haven't mentioned something specific that you have questions about, though.
The actual code is online here: Chapter 5. Objects and Object-Orientation
You still haven't mentioned something specific that you have questions about, though.
Author
pretty much everything....
when to use __init__
where/when to use .self in the class when defining things
when defining things...when do i need arguments
how to edit or things in the class outside the class
which is why i was asking for any good articles/books/anything about them
when to use __init__
where/when to use .self in the class when defining things
when defining things...when do i need arguments
how to edit or things in the class outside the class
which is why i was asking for any good articles/books/anything about them
Think Python covers classes in three chapters and it's free! Definately worth a look:
http://www.greenteapress.com/thinkpython/thinkpython.pdf
http://www.greenteapress.com/thinkpython/thinkpython.pdf
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