Objects/codeobject.c

cpython 3.14 @ ab2d84fe1023/Objects/codeobject.c ↗

Objects/codeobject.c defines PyCodeObject, the compiled representation of a Python function or module. It owns the bytecode array, constant pool, name tables, and position table. The adaptive specialization machinery in Python 3.12+ added per-instruction counter fields that live alongside the bytecode.

Map

Lines	Symbol	Role
1-300	_PyCode_New, PyCode_NewWithPosOnlyArgs	Code object construction and validation
301-600	Position table (co_linetable) encoding	Compact source-location encoding
601-900	co_qualname, co_firstlineno	Qualified name and source location
901-1200	_PyCode_GetFreevars, cell/free var tables	Closure variable access
1201-1600	Adaptive counters, _PyCode_Quicken	Specialization counter allocation

Reading

co_linetable encoding

Instead of a separate co_lnotab per-instruction array, Python 3.10+ uses a compact co_linetable that encodes (offset, line, end_line, col, end_col) tuples for each instruction span. The _PyCode_InitAddressRange iterator decodes this table.

// CPython: Objects/codeobject.c:342 scan_varint
static unsigned int
scan_varint(const uint8_t *ptr)
{
    unsigned int read = *ptr++;
    unsigned int val = read & 63;
    unsigned int shift = 0;
    while (read & 64) {
        read = *ptr++;
        shift += 6;
        val |= (read & 63) << shift;
    }
    return val;
}

Adaptive specialization counters

In Python 3.12+ each instruction word has an associated _Py_BackoffCounter. When the counter saturates, the specializer replaces the generic opcode with a type-specific variant (e.g. LOAD_ATTR becomes LOAD_ATTR_SLOT). _PyCode_Quicken initializes these counters to their starting values.

co_qualname

co_qualname is the dotted name used in __qualname__, for example OuterClass.inner_method or <locals>.helper. It is stored separately from co_name to allow the two to diverge (a lambda has co_name = '<lambda>' but a meaningful co_qualname).

gopy notes

The gopy code object is defined across compile/compiler.go and used by vm/. The position table (co_linetable) is implemented in compile/flowgraph.go. Adaptive specialization counters are not yet implemented; gopy's dispatch loop uses static opcode dispatch.