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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _init_value(self, key):
 """Initialize a value. Lock must be held by caller."""

        encoded = key.encode('utf-8')
        # Pad to be 8-byte aligned.
        padded = encoded + (b' ' * (8 - (len(encoded) + 4) % 8))
        value = struct.pack('i{0}sd'.format(len(padded)).encode(), len(encoded), padded, 0.0)
        while self._used + len(value) > self._capacity:
            self._capacity *= 2
            self._f.truncate(self._capacity)
            self._m = mmap.mmap(self._f.fileno(), self._capacity)
        self._m[self._used:self._used + len(value)] = value

        # Update how much space we've used.
        self._used += len(value)
        _pack_integer(self._m, 0, self._used)
        self._positions[key] = self._used - 8