Objects/typevarobject.c

cpython 3.14 @ ab2d84fe1023/Objects/typevarobject.c ↗

Objects/typevarobject.c provides C-level implementations of TypeVar, ParamSpec, TypeVarTuple, and TypeAliasType introduced in PEP 695 (Python 3.12+). These are the objects created by type T = ... and def f[T](...) syntax.

Map

Lines	Symbol	Role
1-300	TypeVarObject struct, typevar_new	TypeVar construction with bounds and constraints
301-550	typevar_repr, typevar_mro_entries	Display and generic alias creation
551-750	ParamSpecObject, TypeVarTupleObject	Variadic type parameters
751-950	TypeAliasTypeObject	type X = Y alias syntax
951-1100	typevar_subscript	TypeVar[int] subscription returns GenericAlias

Reading

TypeVar with bound and constraints

// CPython: Objects/typevarobject.c:78 TypeVarObject
typedef struct {
    PyObject_HEAD
    PyObject *name;
    PyObject *bound;         /* T = TypeVar('T', bound=X) */
    PyObject *evaluate_bound; /* lazy eval for PEP 649 annotations */
    PyObject *constraints;   /* T = TypeVar('T', X, Y) */
    PyObject *evaluate_constraints;
    unsigned char covariant;
    unsigned char contravariant;
    unsigned char infer_variance;
} TypeVarObject;

PEP 695 type T = X

type T = X compiles to TypeAliasType('T', lambda: X). The lambda defers evaluation of the right-hand side, implementing PEP 649 lazy annotation semantics.

// CPython: Objects/typevarobject.c:760 TypeAliasTypeObject
typedef struct {
    PyObject_HEAD
    PyObject *name;
    PyObject *type_params;   /* tuple of TypeVar/ParamSpec/TypeVarTuple */
    PyObject *compute_value; /* callable that returns the aliased type */
    PyObject *value;         /* cached result, or NULL if not yet computed */
} TypeAliasTypeObject;

__type_params__

Functions and classes defined with [T, ...] syntax have a __type_params__ tuple containing the TypeVar/ParamSpec/TypeVarTuple objects. The compiler emits COPY_FREE_VARS and LOAD_DEREF to capture these into the function.

gopy notes

Not yet ported. typevarobject.c is needed for full PEP 695 syntax support. The gopy compiler would need to emit the __type_params__ tuple and handle type T = X aliasing. Planned path: objects/typevar.go.