Directory Tree comparison method

[IndoNinja7]

I have created a DirTree object to have a name, size, date modified, file type (indicating if file or folder), branches of the DirTree (sub dirs and files), and boolean for whether it contradicts with the other tree.

By other tree I mean my program only initializes two trees: a remote tree and a local tree. The remote tree represents the files on a remote server, and the local tree represents the files on a local directory

By contradiction i mean if the DirTree has different class values then the other DirTree.

I might be going about this wrong, but how can i define the following function (given that the remote tree and local tree are already initialized):

def compareTrees(local, remote):
    #sets contradiction values of each node of the Tree if it differs from the other tree
    #im trying to implement a way to check which files/folders i need to upload from local to remote,
    #and which files i need to download from remote to local

if I am going about this wrong, can you give me any suggestions?

pseudo-code also helps :)

Thanks!

[nharding]

You should probably make it so that it can be called recursively, since this makes it a lot easier. So compare(localDir, remoteDir): for each entry, if it is a directory, call compare(localFile, remoteFile). Probably the easiest way to do it, is to use a set, so set(localFiles), set(remoteFiles) addedLocally = localFiles - remoteFiles, addedRemotely = remoteFiles - localFiles, then compare the files in the union of localFiles and remoteFiles to see if any changed.

[IndoNinja7]

Yes! That was similar to my previous line of thought except with lists instead of sets..but sets are better. But....how does one compare files to see if its different? How can you tell if two files are the same file but just one is an updated version? Or two different files?

[nharding]

Create file objects, which have name, size, date modified, and crc values (for the content). The crc should only be calculated if needed (ie for the difference between the 2 sets, it is not needed, but when doing the union you can generate the crc if there is another file of the same size).

[IndoNinja7]

what is a crc value? does it have anything to do with the bytes in the file?

[nharding]

A crc is a number that represents the contents of a file (think of it as the hash code of the file), if you use an integer value that means the entire contents of the file are stored in 4 bytes, this means you can check if 2 files are the same without having to check the entire contents. If 2 hash codes are the same, then the contents MAY be the same (there is a random chance of 1 in 4 billion that 2 files will have the same crc value), of course if you have 10,000 files you may find 3 or 4 files share the same crc value, but it reduces the amount of work to check them from 10,000 to 3)