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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 AFF4AddChild(self, subject, child, extra_attributes=None):
 """Adds a child to the specified parent."""

    precondition.AssertType(child, Text)

    attributes = {
        DataStore.AFF4_INDEX_DIR_TEMPLATE %
        child: [DataStore.EMPTY_DATA_PLACEHOLDER]
    }
    if extra_attributes:
      attributes.update(extra_attributes)
    self.MultiSet(subject, attributes)