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1. How To Use Python Wrapper
2. Python Wrappers For C Tutorial
3. Python Wrapper Class

The problem is that these are stored in struct wrapperbase, which is common for all wrappers of a specific slot (for example, the same wrapperbase is used for str.eq and int.eq). Solution: rethink the slot wrapper class to allow docstrings (and text signatures) for each instance separately. A slot wrapper is installed in the dict of an extension type to access a special method implemented in C. For example, object.init or Integer.lt. Note that slot wrappers are always unbound (there is a bound variant called method-wrapper). These names can't point directly to the C functions; instead they point to (you guessed it) special 'slot wrapper' objects, which encapsulate all the information necessary to actually call the C functions from Python. The one exception to this is new, which is done differently for reasons that I'll cover in a future entry. Python 2’s range function returned a list, which means the expressions above would make very very large lists. Python 3’s range works like Python 2’s xrange (though they’re a bit different) in that numbers are computed lazily as we loop over these range objects. Built-ins overlooked by new Pythonistas.

There are a large number of structures which are used in the definition ofobject types for Python. This section describes these structures and how theyare used.

All Python objects ultimately share a small number of fields at the beginningof the object’s representation in memory. These are represented by thePyObject and PyVarObject types, which are defined, in turn,by the expansions of some macros also used, whether directly or indirectly, inthe definition of all other Python objects.

All object types are extensions of this type. This is a type whichcontains the information Python needs to treat a pointer to an object as anobject. In a normal “release” build, it contains only the object’sreference count and a pointer to the corresponding type object. Itcorresponds to the fields defined by the expansion of the PyObject_HEADmacro.

This is an extension of PyObject that adds the ob_sizefield. This is only used for objects that have some notion of length.This type does not often appear in the Python/C API. It corresponds to thefields defined by the expansion of the PyObject_VAR_HEAD macro.

These macros are used in the definition of PyObject andPyVarObject:

This is a macro which expands to the declarations of the fields of thePyObject type; it is used when declaring new types which representobjects without a varying length. The specific fields it expands to dependon the definition of Py_TRACE_REFS. By default, that macro isnot defined, and PyObject_HEAD expands to:

When Py_TRACE_REFS is defined, it expands to:

This is a macro which expands to the declarations of the fields of thePyVarObject type; it is used when declaring new types whichrepresent objects with a length that varies from instance to instance.This macro always expands to:

Note that PyObject_HEAD is part of the expansion, and that its ownexpansion varies depending on the definition of Py_TRACE_REFS.

This macro is used to access the ob_type member of a Python object.It expands to:

New in version 2.6.

This macro is used to access the ob_refcnt member of a Pythonobject.It expands to:

New in version 2.6.

This macro is used to access the ob_size member of a Python object.It expands to:

New in version 2.6.

This is a macro which expands to initialization values for a newPyObject type. This macro expands to:

This is a macro which expands to initialization values for a newPyVarObject type, including the ob_size field.This macro expands to:

Type of the functions used to implement most Python callables in C.Functions of this type take two PyObject* parameters and returnone such value. If the return value is NULL, an exception shall havebeen set. If not NULL, the return value is interpreted as the returnvalue of the function as exposed in Python. The function must return a newreference.

Structure used to describe a method of an extension type. This structure hasfour fields:

The ml_meth is a C function pointer. The functions may be of differenttypes, but they always return PyObject*. If the function is not ofthe PyCFunction, the compiler will require a cast in the method table.Even though PyCFunction defines the first parameter asPyObject*, it is common that the method implementation uses thespecific C type of the self object.

The ml_flags field is a bitfield which can include the following flags.The individual flags indicate either a calling convention or a bindingconvention. Of the calling convention flags, only METH_VARARGS andMETH_KEYWORDS can be combined. Any of the calling convention flagscan be combined with a binding flag.

This is the typical calling convention, where the methods have the typePyCFunction. The function expects two PyObject* values.The first one is the self object for methods; for module functions, it isthe module object. The second parameter (often called args) is a tupleobject representing all arguments. This parameter is typically processedusing PyArg_ParseTuple() or PyArg_UnpackTuple().

Methods with these flags must be of type PyCFunctionWithKeywords.The function expects three parameters: self, args, and a dictionary ofall the keyword arguments. The flag is typically combined withMETH_VARARGS, and the parameters are typically processed usingPyArg_ParseTupleAndKeywords().

Methods without parameters don’t need to check whether arguments are given ifthey are listed with the METH_NOARGS flag. They need to be of typePyCFunction. The first parameter is typically named self andwill hold a reference to the module or object instance. In all cases thesecond parameter will be NULL.

Methods with a single object argument can be listed with the METH_Oflag, instead of invoking PyArg_ParseTuple() with a 'O' argument.They have the type PyCFunction, with the self parameter, and aPyObject* parameter representing the single argument.

This calling convention is deprecated. The method must be of typePyCFunction. The second argument is NULL if no arguments aregiven, a single object if exactly one argument is given, and a tuple ofobjects if more than one argument is given. There is no way for a functionusing this convention to distinguish between a call with multiple argumentsand a call with a tuple as the only argument.

These two constants are not used to indicate the calling convention but thebinding when use with methods of classes. These may not be used for functionsdefined for modules. At most one of these flags may be set for any givenmethod.

The method will be passed the type object as the first parameter ratherthan an instance of the type. This is used to create class methods,similar to what is created when using the classmethod() built-infunction.

New in version 2.3.

The method will be passed NULL as the first parameter rather than aninstance of the type. This is used to create static methods, similar towhat is created when using the staticmethod() built-in function.

One other constant controls whether a method is loaded in place of anotherdefinition with the same method name.

The method will be loaded in place of existing definitions. WithoutMETH_COEXIST, the default is to skip repeated definitions. Since slotwrappers are loaded before the method table, the existence of asq_contains slot, for example, would generate a wrapped method named__contains__() and preclude the loading of a correspondingPyCFunction with the same name. With the flag defined, the PyCFunctionwill be loaded in place of the wrapper object and will co-exist with theslot. This is helpful because calls to PyCFunctions are optimized morethan wrapper object calls.

New in version 2.4.

Structure which describes an attribute of a type which corresponds to a Cstruct member. Its fields are:

type can be one of many T_ macros corresponding to various Ctypes. When the member is accessed in Python, it will be converted to theequivalent Python type.

T_OBJECT and T_OBJECT_EX differ in thatT_OBJECT returns None if the member is NULL andT_OBJECT_EX raises an AttributeError. Try to useT_OBJECT_EX over T_OBJECT because T_OBJECT_EXhandles use of the del statement on that attribute more correctlythan T_OBJECT.

flags can be 0 for write and read access or READONLY forread-only access. Using T_STRING for type impliesREADONLY. Only T_OBJECT and T_OBJECT_EXmembers can be deleted. (They are set to NULL).

How To Use Python Wrapper

Structure to define property-like access for a type. See also description ofthe PyTypeObject.tp_getset slot.

Python Wrappers For C Tutorial

The get function takes one PyObject* parameter (theinstance) and a function pointer (the associated closure):

It should return a new reference on success or NULL with a set exceptionon failure.

set functions take two PyObject* parameters (the instance andthe value to be set) and a function pointer (the associated closure):

In case the attribute should be deleted the second parameter is NULL.Should return 0 on success or -1 with a set exception on failure.

Return a bound method object for an extension type implemented in C. Thiscan be useful in the implementation of a tp_getattro ortp_getattr handler that does not use thePyObject_GenericGetAttr() function.

Python Wrapper Class