Parser and Serializer for Minecraft's binary format
$ python3
>>> import nbt
>>> f = nbt.read("level.dat")
>>> f["Data"]["Player"]["Score"]
TAG_Int("Score"): 292
>>> f["Data"]["Player"]["Score"] = 300
>>> f["Data"]["Player"]["Score"]
TAG_Int("Score"): 300
>>> nbt.write("level.dat", f)
>>>
Alternatively, you can use the lazynbt approach, inspired by lazyjson: Instead of explicitly reading and writing, you just keep a reference to the file, which is read every time when it changed and written back to disk when the user makes changes.
$ python3
>>> import lazynbt
>>> f = lazynbt.File("level.dat")
>>> f["Data"]["Player"]["Score"]
lazynbt.File("level.dat", ["Data", "Player", "Score"])
>>> f["Data"]["Player"]["Score"].value()
TAG_Int("Score"): 292
>>> f["Data"]["Player"]["Score"] = 300
>>>
As you might notice, when the user assigns a new value for some tag, it is not assigned directly, but transformed into a matching tag. Since in these examples the tag type was TAG_Int, and the user provided a Python integer, that was no problem. nbt.py will complain if you give it a wrong type, e.g. a non-integer float for a TAG_Int or something entirely different. Alternatively, you may also directly assign nbt.Tag values.
WTFPL, but attribution would be nice, and if you use it, please tell me.