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Extending and Embedding the Python Interpreter |  |
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Extending and Embedding the Python Interpreter | |
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This section aims to give a quick fly-by on the various type methods you can implement and what they do.
Here is the definition of PyTypeObject, with some fields only used in debug builds omitted:
typedef struct _typeobject {
PyObject_VAR_HEAD
char *tp_name; /* For printing */
int tp_basicsize, tp_itemsize; /* For allocation */
/* Methods to implement standard operations */
destructor tp_dealloc;
printfunc tp_print;
getattrfunc tp_getattr;
setattrfunc tp_setattr;
cmpfunc tp_compare;
reprfunc tp_repr;
/* Method suites for standard classes */
PyNumberMethods *tp_as_number;
PySequenceMethods *tp_as_sequence;
PyMappingMethods *tp_as_mapping;
/* More standard operations (here for binary compatibility) */
hashfunc tp_hash;
ternaryfunc tp_call;
reprfunc tp_str;
getattrofunc tp_getattro;
setattrofunc tp_setattro;
/* Functions to access object as input/output buffer */
PyBufferProcs *tp_as_buffer;
/* Flags to define presence of optional/expanded features */
long tp_flags;
char *tp_doc; /* Documentation string */
/* call function for all accessible objects */
traverseproc tp_traverse;
/* delete references to contained objects */
inquiry tp_clear;
/* rich comparisons */
richcmpfunc tp_richcompare;
/* weak reference enabler */
long tp_weaklistoffset;
} PyTypeObject;
Now that's a lot of methods. Don't worry too much though - if you have a type you want to define, the chances are very good that you will only implement a handful of these.
As you probably expect by now, I'm going to go over this line-by-line, saying a word about each field as we get to it.
char *tp_name; /* For printing */
The name of the type - as mentioned in the last section, this will appear in various places, almost entirely for diagnostic purposes. Try to choose something that will be helpful in such a situation!
int tp_basicsize, tp_itemsize; /* For allocation */
These fields tell the runtime how much memory to allocate when new objects of this typed are created. Python has some builtin support for variable length structures (think: strings, lists) which is where the tp_itemsize field comes in. This will be dealt with later.
Now we come to the basic type methods - the ones most extension types will implement.
destructor tp_dealloc;
printfunc tp_print;
getattrfunc tp_getattr;
setattrfunc tp_setattr;
cmpfunc tp_compare;
reprfunc tp_repr;
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Extending and Embedding the Python Interpreter | |
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