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Minecraft.Print() is a project by Cody Sumter and Jason Boggess in the MIT Media Lab. 

They attempt to create a bridge between Minecraft and the real world, via 3D printers. A Minecraft player defines a 3D space to be printed, after which the software extracts the object, structure, or other creation from the virtual space and creates 3D-printable version. 

By placing a combination of specific blocks (obsidian, diamond, gold, iron) at two points you can define the 3 dimensional area to print.Tthen the python script looks for everything that exists within those boundaries and generates a .stl file. You can use Minecraft.Print() to print out anything you create.

You can download python script from this link.

Source: 

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