Using zstandard to compress a file in Python

So I'm using the zstandard python library, and I've written a helper class and function to use contexts to decompress files.

class ZstdReader:
    def __init__(self, filename):
        self.filename = filename

    def __enter__(self):
        self.f = open(self.filename, 'rb')
        dctx = zstd.ZstdDecompressor()
        reader = dctx.stream_reader(self.f)
        return io.TextIOWrapper(reader, encoding='utf-8')

    def __exit__(self, *a):
        self.f.close()
        return False

def openZstd(filename, mode='rb'):
    if 'w' in mode:
        return ZstdWriter(filename)
    return ZstdReader(filename)

This works really well and allows me to just use with openZstd('filename.zst', 'rb') as f: before using the file f for json dumping and loading. I'm however having issues generalizing this to writing, I've tried following the documentation in the same way I did so far but something is not working. Here's what I've tried:

class ZstdWriter:
    def __init__(self, filename):
        self.filename = filename

    def __enter__(self):
        self.f = open(self.filename, 'wb')
        ctx = zstd.ZstdCompressor()
        writer = ctx.stream_writer(self.f)
        return io.TextIOWrapper(writer, encoding='utf-8')

    def __exit__(self, *a):
        self.f.close()
        return False

When I open a file using this class, and do a json.dump([], f), the file ends up being empty for some reason. I guess one of the steps is swallowing my input, but have no idea what it could possibly be.

As suggested by jasonharper in the comments, you have to flush both the io wrapper and the writer itself, as follows:

s = json.dumps({})
iw = io.TextIOWrapper(writer, encoding="utf-8")
iw.write(s)

iw.flush()
writer.flush(zstd.FLUSH_FRAME)
f.close()

This results on the data being in the file, and the file being complete.