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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 create_block(mc, block_id, subtype=None):
 """Build a block with the specified id and subtype under the player in the Minecraft world. Subtype is optional and can be specified as None to use the default subtype for the block. """

    # Get player tile position and real position.
    ptx, pty, ptz = mc.player.getTilePos()
    px, py, pz = mc.player.getPos()
    # Create block at current player tile location.
    if subtype is None:
        mc.setBlock(ptx, pty, ptz, block_id)
    else:
        mc.setBlock(ptx, pty, ptz, block_id, subtype)
    # Move the player's real positon up one block.
    mc.player.setPos(px, py+1, pz)