Objects/codeobject.c (part 4)

Source:

cpython 3.14 @ ab2d84fe1023/Objects/codeobject.c ↗

This annotation covers code object construction. See objects_codeobject3_detail for PyCodeObject field layout, co_code, co_consts, and co_linetable.

Map

Lines	Symbol	Role
1-80	localspluskinds	Classify locals: fast, cell, free, hidden
81-180	co_positions	Per-instruction (line, col, end_line, end_col)
181-280	co_qualname	Qualified name for nested functions/classes
281-380	PyCode_NewWithPosOnlyArgs	Constructor with positional-only argument count
381-500	code.replace	Create a modified copy of a code object

Reading

localspluskinds

// CPython: Objects/codeobject.c:180 localspluskinds encoding
/* co_localspluskinds: bytes, one per localsplusname entry.
   Each byte is a bitfield:
   CO_FAST_LOCAL    = 0x20: regular local variable
   CO_FAST_CELL     = 0x40: cell variable (referenced by inner function)
   CO_FAST_FREE     = 0x80: free variable (from enclosing function)
   CO_FAST_HIDDEN   = 0x10: hidden local (implicit, e.g. .type_params) */

localspluskinds replaces the separate co_varnames/co_cellvars/co_freevars tuples from Python 3.10. A single array with kind bits allows the eval loop to handle all variable types with one slot lookup.

co_positions

// CPython: Objects/codeobject.c:380 _PyCode_InitAddressRange
/* co_positions() returns an iterator of (line, end_line, col, end_col) tuples,
   one per instruction. Used by tracebacks and coverage tools.
   Encoded as a delta-compressed byte stream in co_exceptiontable (shared). */

co.co_positions() returns fine-grained source location for each instruction. This enables precise error highlighting: the ^ in SyntaxError points to the exact expression, not just the line. The encoding is space-efficient using varint deltas.

co_qualname

// CPython: Objects/codeobject.c:240 qualname
/* co_qualname: the dotted name including enclosing class/function names.
   'Foo.bar' for a method, 'Foo.<locals>.inner' for a nested function.
   co_name: just the simple name ('bar', 'inner').
   Used by repr(), __qualname__ attribute on functions/classes. */

co_qualname was added in Python 3.3. A lambda inside a function has co_qualname like f.<locals>.<lambda>. This allows repr(f) to show <function Foo.method at 0x...> instead of just <function method at 0x...>.

code.replace

// CPython: Objects/codeobject.c:680 code_replace_impl
static PyObject *
code_replace_impl(PyCodeObject *self, ...)
{
    /* Return a copy of the code object with specified fields replaced.
       Used by functools.wraps, dataclasses, and testing. */
    return PyCode_NewWithPosOnlyArgs(
        co_argcount, co_posonlyargcount, co_kwonlyargcount,
        co_nlocals, co_stacksize, co_flags,
        co_code, co_consts, co_names, ...);
}

code.replace(co_name='new_name') creates a new code object with all fields copied except those specified. Used by functools.wraps to fix __wrapped__.__code__.co_name and by testing frameworks to inject instrumentation.

gopy notes

localspluskinds is objects.Code.LocalsplusKinds (a []byte) in objects/function.go. co_positions is encoded in objects.Code.Positions. co_qualname is objects.Code.QualName. code.replace is objects.CodeReplace which returns a new *objects.Code with fields overridden.