Differences From Python

Cobble borrows Python’s look, but programs run as Minecraft commands. Values are scoreboard integers or storage entries, and every function is a .mcfunction file.

Not Supported

These fail with a diagnostic before compilation:

• classes, decorators, try/except/finally, with, lambda, yield, async, await, break, continue, raise, assert, del, and nonlocal;
• default parameter values, duplicate parameter names, *args, and **kwargs;
• list and dict comprehensions;
• for ... else;
• dotted or relative imports, import aliases, and import a, b;
• recursion, direct or through other functions.

cobble check --experimental-python-compat lists the supported Python-like constructs and suggests a Cobble rewrite for unsupported ones; see Experimental Features.

Values And Expressions

• Numbers are 32-bit integers. Floats are truncated, with a warning.
• Lists and maps live in storage. Subscripts work when the base resolves to a storage path. List and string indexes may be literals, constants, or runtime integers such as items[i]; map keys may be attributes, string literals, or runtime strings such as config[key].
• Functions return integers only. Use storage or a module variable for other results.
• A bare expression such as score + 1 produces no command and is rejected. Use an assignment, a call, a raw command, or pass.
• for loops iterate range(...), literal arrays, and storage-backed lists.
• All of a pack’s variables share one scoreboard objective, so there is no local scope; see The global Keyword.
• while loops and runtime for loops compile to functions that call themselves, and every iteration runs in the same game tick.

Browser Compiler

The browser compiler at /try compiles one in-memory file. Check projects with local imports using the CLI, which resolves files from disk.