Add option to write to kdbx databases

[wget]

Sometimes, we need to write to kdbx file. This library doesn't allow this ability without having to declare yet another file descriptor, just to be able to write.

This patch adds the ability to reuse the existing file descriptor opened in pykeepass's open context manager.

[Evidlo]

I think a better solution might be something like this:

def open(filename, mode='rw', **credentials):
    """
    A contextmanager to open the KeePass file with `filename`. Use a `password`
    and/or `keyfile` named argument for decryption.
    
    Files are identified using their signature and a reader suitable for 
    the file format is intialized and returned.
    
    Note: `keyfile` is currently not supported for v3 KeePass files.
    """
    kdb = None
    try:
        with io.open(filename, mode) as stream:
            signature = common.read_signature(stream)
            cls = get_kdb_reader(signature)
            kdb = cls(stream, **credentials)
            yield kdb
            kdb.close()
    except:
        if kdb:
            kdb.close()
        raise

[wget]

@Evidlo Ok done as well.

[Evidlo]

The mode should actually be 'rb+' as per the io documentation.

Be sure to test your code before making a PR. I'm partially at fault too for approving it before testing.

[pschmitt]

Please update that to rb+

[wget]

@pschmitt Done.
@Evidlo Btw, I was using r+b in my previous PR and I tested it. But yes, I have to admit I haven't tested for rw nor rb+ (only r+b has been tested).

[pschmitt]

thanks!