Now let us examine the structures related to class operations.

typedef struct {
PyObject_HEAD
PyObject *cl_bases; /* A tuple of class objects */
PyObject *cl_dict; /* A dictionary */
PyObject *cl_name; /* A string */
/* The following three are functions or NULL */
PyObject *cl_getattr;
PyObject *cl_setattr;
PyObject *cl_delattr;
PyObject *cl_weakreflist; /* List of weak references */
} PyClassObject;

typedef struct {
PyObject_HEAD
PyClassObject *in_class; /* The class object */
PyObject *in_dict; /* A dictionary */
PyObject *in_weakreflist; /* List of weak references */
} PyInstanceObject;

typedef struct {
PyObject_HEAD
PyObject *im_func; /* The callable object implementing the method */
PyObject *im_self; /* The instance it is bound to, or NULL */
PyObject *im_class; /* The class that asked for the method */
PyObject *im_weakreflist; /* List of weak references */
} PyMethodObject;

The structures are found in Include/classobject.h and are self explanatory.

Open the file Objects/classobject.c and insert a breakpoint in line number 34. Debug the application and type the expression:

class a:

pass

Observe how the breakpoint is trapped and a new class is created by going through the flow. Also insert breakpoints in other methods of the file and see how the class is manipulated and used.

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