ZeroFile

class ZeroFile():

    def __init__(self, file_size):
        self.file_size = file_size
        self._buf = b'\0'
        self.position = 0

    def tell(self):
        return self.position

    def read(self, size=-1):
        remaining = self.file_size - self.position
        if remaining == 0:
            return b''
        if not size or size < 0:
            size = remaining
        else:
            size = min(size, remaining)
        self.position += size

        return b'\0' * size

    def seek(self, offset, whence=0):
        if whence == 0:
            self.position = 0 + offset
        if whence == 1:
            self.position = self.position + offset
        if whence == 2:
            self.position = self.file_size + offset