Arbitrarily large fake filelike python

fakefile.py

class FakeFile:
    def __init__(self, size, repeat=b'0'):
        self.loc = 0
        self.size = size
        self.repeat = repeat
        self.closed = False

    def fileno(self):
        raise OSError()

    def write(self, data):
        raise OSError()

    def read(self, size=None):
        if size is None:
            size = self.size
        end = min(self.loc + size, self.size)
        size = end - self.loc
        if size <= 0:
            return b''
        self.loc += size
        return self.repeat * size

    def seek(self, offset, whence=SEEK_SET):
        if whence == SEEK_SET:
            self.loc = offset
        elif whence == SEEK_END:
            self.loc = self.size - offset
        elif whence == SEEK_CUR:
            self.loc += offset
        return

    def seekable(self):
        return True

    def close(self):
        self.closed = True

    def tell(self):
        return self.loc

This was useful when testing things like upload limits, because I didn't have enough RAM to use a BytesIO and properly break things.