TurboPython - a Python-to-C++ compiler

How it differs from Python

Python syntax with static types and a strict ownership model.

Type annotations are required on function parameters, return types, and class fields; an unannotated integer literal defaults to a 32-bit int32. Beyond these rules, most code reads like standard Python—minus Python's dynamic runtime features. Where a construct diverges from the static type and ownership model, the compiler reports it, and its diagnostics name the required change.

No pip packages

Packages written for CPython, such as numpy or requests, cannot be imported. Everything a program imports is compiled together with it. A dependency has to be written in TurboPython or ported to it. What ships today is a subset of the standard library and TurboPython's own tplib libraries; Compatibility lists them.

Ownership

Python reclaims objects automatically through reference counting, so a name is just a shared reference. TurboPython has no garbage collector: every value has exactly one owner — a function frame, a field, or a container — and the owner controls when it is freed. Locals and parameters still alias as they do in Python; persistent storage owns its values. Three cases follow, each shown with the compiler's actual output.

def make() -> Obj:
    o = Obj(1)
    return o   # freed when make returns

def make() -> Own[Obj]:
    o = Obj(1)
    return o   # ownership moves to the caller

o lives in make's frame and is freed when the function returns; returning it by reference would leave a dangling pointer. Own[Obj] hands the value itself to the caller, who becomes its owner.

class Cache:
    item: Tag
    def __init__(self, t: Tag) -> None:
        self.item = t   # Python would share a reference

class Cache:
    item: Tag
    def __init__(self, t: Own[Tag]) -> None:
        self.item = t   # the field takes ownership

A field outlives the call that sets it, so it must own its value. Declaring the parameter Own[Tag] transfers the caller's object in; copy(t) is the alternative when the caller keeps its own. Fields are declared as typed class attributes and set in __init__ — there is no __dict__, so each one is a fixed, typed slot.

l: list[Obj] = []
o = Obj(1)
l.append(o)   # implicit copy: o is used below
o.x = 99

l: list[Obj] = []
o = Obj(1)
l.append(copy(o))
o.x = 99      # the list holds its own copy

A list stores objects, not references, so the append copies either way — where Python would share the same object. copy() doesn't introduce the copy; it makes the unavoidable one explicit and clears the warning. If o weren't used afterward, it would be moved into the list instead — no copy at all.

Other differences

Ownership is the conceptual shift. The rest are smaller, mechanical rules — the type system's requirements, and the constraints a compiled language places on Python's more dynamic features. They become familiar within the first few files.

🤖 AI assistants are supported. tpy --install-agent-docs docs writes a TurboPython primer alongside the code — the Python-to-TPy delta, the ownership rules, and the idioms an assistant needs to generate correct TurboPython.