Deep Internal Analysis: CPython Architecture & PyObject Mechanics

PyObject Memory Architecture

In the CPython runtime, every single variable is fundamentally a pointer to an underlying C struct named PyObject.

• ob_refcnt: The reference counter tracking how many active identifiers point to this object in memory. When this counter hits zero, free is immediately triggered.
• ob_type: A pointer to the underlying Type Object, defining the literal vtable of functions valid for this instance.

The CEval Virtual Machine Loop

• The Evaluation Loop: The internal compiler converts .py files into Bytecode instructions, which are passed to the central runtime evaluation loop _PyEval_EvalFrameDefault.
• Dynamic Jump Dispatch: During every single VM step, bytecode instructions are parsed and routed to their underlying C implementations via a massive jump table. This additional dispatch layer accounts for Python's runtime performance overhead relative to bare-metal C.

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                   PyObject C-STRUCT TOPOLOGY
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  typedef struct _object {
      _PyObject_HEAD_EXTRA
      Py_ssize_t ob_refcnt;   ──> Garbage collection active monitor
      struct _typeobject *ob_type; ──> Type definitions & method table
  } PyObject;

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