A SIP specification consists of some C/C++ type and function declarations and some :ref:`directives <ref-directives>`. The declarations may contain :ref:`annotations <ref-annotations>` which provide SIP with additional information that cannot be expressed in C/C++. SIP does not implement a full C/C++ parser.
The following is a semi-formal description of the syntax of a specification file.
specification ::= {module-statement} module-statement ::= [module-directive | statement] module-directive ::= [ :directive:`%CompositeModule` | :directive:`%Copying` | :directive:`%DefaultDocstringFormat` | :directive:`%DefaultDocstringSignature` | :directive:`%DefaultEncoding` | :directive:`%DefaultMetatype` | :directive:`%DefaultSupertype` | :directive:`%ExportedHeaderCode` | :directive:`%ExportedTypeHintCode` | :directive:`%Extract` | :directive:`%Feature` | :directive:`%HideNamespace` | :directive:`%Import` | :directive:`%Include` | :directive:`%InitialisationCode` | :directive:`%License` | :directive:`%MinimumABIVersion` | :directive:`%Module` | :directive:`%ModuleCode` | :directive:`%ModuleHeaderCode` | :directive:`%Platforms` | :directive:`%PreInitialisationCode` | :directive:`%PostInitialisationCode` | :directive:`%Timeline` | :directive:`%TypeHintCode` | :directive:`%UnitCode` | :directive:`%UnitPostIncludeCode` | :directive:`%VirtualErrorHandler` | mapped-type | mapped-type-template] statement :: [class-statement | function | variable] class-statement :: [ :directive:`%If` | class | class-template | enum | namespace | opaque-class | operator | struct | union | typedef | exception] class ::= classname [:super-classes] [class-annotations] { {class-line} };super-classes ::= [public | protected | private] name [,super-classes] class-line ::= [ class-statement | :directive:`%BIGetBufferCode` | :directive:`%BIReleaseBufferCode` | :directive:`%ConvertFromTypeCode` | :directive:`%ConvertToSubClassCode` | :directive:`%ConvertToTypeCode` | :directive:`%Docstring` | :directive:`%FinalisationCode` | :directive:`%GCClearCode` | :directive:`%GCTraverseCode` | :directive:`%InstanceCode` | :directive:`%PickleCode` | :directive:`%TypeCode` | :directive:`%TypeHeaderCode` | :directive:`%TypeHintCode` | constructor | destructor | method | static-method | virtual-method | special-method | operator | virtual-operator | class-variable | public: | public Q_SLOTS: | public slots: | protected: | protected Q_SLOTS: | protected slots: | private: | private Q_SLOTS: | private slots: | Q_SIGNALS: | signals:] constructor ::= [explicit] name( [argument-list] ) [noexcept] [function-annotations] [c++-constructor-signature] ; [:directive:`%Docstring`] [:directive:`%MethodCode`] c++-constructor-signature ::= [( [argument-list] )]destructor ::= [virtual] ~name() [noexcept] [= 0] [function-annotations] ; [:directive:`%MethodCode`] [:directive:`%VirtualCatcherCode`] method ::= [Q_SIGNAL] [Q_SLOT] typename( [argument-list] ) [const] [final] [noexcept] [= 0] [function-annotations] [c++-signature] ; [:directive:`%Docstring`] [:directive:`%MethodCode`] c++-signature ::= [type( [argument-list] )]static-method ::= staticfunctionvirtual-method ::= [Q_SIGNAL] [Q_SLOT] virtualtypename( [argument-list] ) [const] [final] [noexcept] [= 0] [function-annotations] [c++-signature] ; [:directive:`%MethodCode`] [:directive:`%VirtualCatcherCode`] [:directive:`%VirtualCallCode`] special-method ::= typespecial-method-name( [argument-list] ) [function-annotations] ; [:directive:`%MethodCode`] special-method-name ::= [__abs__ | __add__ | __and__ | __aiter__ | __anext__ | __await__ | __bool__ | __call__ | __contains__ | __delattr__ | __delitem__ | __div__ | __eq__ | __float__ | __floordiv__ | __ge__ | __getattr__ | __getattribute__ | __getitem__ | __gt__ | __hash__ | __iadd__ | __iand__ | __idiv__ | __ifloordiv__ | __ilshift__ | __imatmul__ | __imod__ | __imul__ | __index__ | __int__ | __invert__ | __ior__ | __irshift__ | __isub__ | __iter__ | __itruediv__ | __ixor__ | __le__ | __len__ | __lshift__ | __lt__ | __matmul | __mod__ | __mul__ | __ne__ | __neg__ | __next__ | __or__ | __pos__ | __repr__ | __rshift__ | __setattr__ | __setitem__ | __str__ | __sub__ | __truediv__ | __xor__] operator ::= operator-type( [argument-list] ) [const] [final] [noexcept] [function-annotations] ; [:directive:`%MethodCode`] virtual-operator ::= virtualoperator-type( [argument-list] ) [const] [final] [noexcept] [= 0] [function-annotations] ; [:directive:`%MethodCode`] [:directive:`%VirtualCatcherCode`] [:directive:`%VirtualCallCode`] operatator-type ::= [ operator-function | operator-cast ] operator-function ::= typeoperatoroperator-nameoperator-cast ::= operatortypeoperator-name ::= [+ | - | * | / | % | & | | | ^ | << | >> | += | -= | *= | /= | %= | &= | |= | ^= | <<= | >>= | ~ | () | [] | < | <= | == | != | > | >>= | =] class-variable ::= [static] variableclass-template :: = template<type-list>classmapped-type :: = :directive:`%MappedType`base-type [mapped-type-annotations] { {mapped-type-line} };mapped-type-line ::= [ :directive:`%If` | :directive:`%ConvertFromTypeCode` | :directive:`%ConvertToTypeCode` | :directive:`%ReleaseCode` | :directive:`%TypeCode` | :directive:`%TypeHeaderCode` | enum | function | variable] mapped-type-template :: = template<type-list>mapped-typeenum ::= enum [enum-key] [name] [enum-annotations] { {enum-line} };enum-key ::= [class | struct] enum-line ::= [:directive:`%If` | name [enum-annotations] ,function ::= typed-name( [argument-list] ) [noexcept] [function-annotations] ; [:directive:`%Docstring`] [:directive:`%MethodCode`] namespace ::= namespacename [{ {namespace-line} }] ;namespace-line ::= [:directive:`%TypeHeaderCode` | statement] opaque-class ::= classscoped-name;struct ::= structname{ {class-line} };union ::= unionname{ {class-line} };typedef ::= typedef [typed-name | function-pointer] typedef-annotations;variable::= typed-name [variable-annotations] ; [:directive:`%AccessCode`] [:directive:`%GetCode`] [:directive:`%SetCode`] exception ::= :directive:`%Exception`exception-name [exception-base] { [:directive:`%TypeHeaderCode`] :directive:`%RaiseCode`};exception-name ::= scoped-nameexception-base ::= ( [exception-name | python-exception] )python-exception ::= [SIP_ArithmeticError | SIP_AssertionError | SIP_AttributeError | SIP_BaseException | SIP_BlockingIOError | SIP_BrokenPipeError | SIP_BufferError | SIP_ChildProcessError | SIP_ConnectionAbortedError | SIP_ConnectionError | SIP_ConnectionRefusedError | SIP_ConnectionResetError | SIP_EnvironmentError | SIP_EOFError | SIP_Exception | SIP_FileExistsError | SIP_FileNotFoundError | SIP_FloatingPointError | SIP_GeneratorExit | SIP_ImportError | SIP_IndentationError | SIP_IndexError | SIP_InterruptedError | SIP_IOError | SIP_IsADirectoryError | SIP_KeyboardInterrupt | SIP_KeyError | SIP_LookupError | SIP_MemoryError | SIP_NameError | SIP_NotADirectoryError | SIP_NotImplementedError | SIP_OSError | SIP_OverflowError | SIP_PermissionError | SIP_ProcessLookupError | SIP_ReferenceError | SIP_RuntimeError | SIP_StandardError | SIP_StopIteration | SIP_SyntaxError | SIP_SystemError | SIP_SystemExit | SIP_TabError | SIP_TimeoutError | SIP_TypeError | SIP_UnboundLocalError | SIP_UnicodeDecodeError | SIP_UnicodeEncodeError | SIP_UnicodeError | SIP_UnicodeTranslateError | SIP_ValueError | SIP_VMSError | SIP_WindowsError | SIP_ZeroDivisionError | SIP_Warning | SIP_BytesWarning | SIP_DeprecationWarning | SIP_FutureWarning | SIP_ImportWarning | SIP_PendingDeprecationWarning | SIP_ResourceWarning | SIP_RuntimeWarning | SIP_SyntaxWarning | SIP_UnicodeWarning | SIP_UserWarning] argument-list ::= argument [,argument-list] [,...] argument ::= type [name] [argument-annotations] [default-value] default-value ::= =expressionexpression ::= [value | valuebinary-operatorexpression] value ::= [unary-operator] simple-valuesimple-value ::= [scoped-name | function-call | real-value | integer-value | boolean-value | string-value | character-value] typed-name::= typenamefunction-pointer::= type(*name)( [type-list] )type-list ::= type [,type-list] function-call ::= scoped-name( [value-list] )value-list ::= value [,value-list] real-value ::= a floating point number integer-value ::= a number boolean-value ::= [true | false] string-value ::= " {character} "character-value ::= 'character'unary-operator ::= [! | ~ | - | + | * | &] binary-operator ::= [- | + | * | / | & | |] argument-annotations ::= see :ref:`ref-arg-annos`class-annotations ::= see :ref:`ref-class-annos`enum-annotations ::= see :ref:`ref-enum-annos`function-annotations ::= see :ref:`ref-function-annos`mapped-type-annotations ::= see :ref:`ref-mapped-type-annos`typedef-annotations ::= see :ref:`ref-typedef-annos`variable-annotations ::= see :ref:`ref-variable-annos`type ::= [const] base-type {*} [&] type-list ::= type [,type-list] base-type ::= [scoped-name | template | structscoped-name | unionscoped-name | char | signed char | unsigned char | wchar_t | int | unsigned | unsigned int | size_t | short | unsigned short | long | unsigned long | long long | unsigned long long | float | double | bool | void | Py_hash_t | Py_ssize_t | PyObject | :stype:`SIP_PYBUFFER` | :stype:`SIP_PYCALLABLE` | :stype:`SIP_PYDICT` | :stype:`SIP_PYENUM` | :stype:`SIP_PYLIST` | :stype:`SIP_PYOBJECT` | :stype:`SIP_PYSLICE` | :stype:`SIP_PYTUPLE` | :stype:`SIP_PYTYPE`] scoped-name ::= name [::scoped-name] template ::= scoped-name<type-list>dotted-name ::= name [.dotted-name] name ::= _A-Za-z {_A-Za-z0-9} Here is a short list of differences between C++ and the subset supported by SIP that might trip you up.
- SIP does not support the use of
[]in types. Use pointers instead.- A global
operatorcan only be defined if its first argument is a class or a named enum that has been wrapped in the same module.- Variables declared outside of a class are effectively read-only.
SIP supports the use of ... as the last part of a function signature. Any remaining arguments are collected as a Python tuple.
SIP supports a number of additional data types that can be used in Python signatures.
.. sip-type:: SIP_PYBUFFER
This is a PyObject * that implements the Python buffer protocol.
.. sip-type:: SIP_PYCALLABLE
This is a PyObject * that is a Python callable object.
.. sip-type:: SIP_PYDICT
This is a PyObject * that is a Python dictionary object.
.. sip-type:: SIP_PYENUM
This is a PyObject * that is a Python enum object.
.. sip-type:: SIP_PYLIST
This is a PyObject * that is a Python list object.
.. sip-type:: SIP_PYOBJECT
This is a PyObject * of any Python type. The type PyObject * can also be used.
.. sip-type:: SIP_PYSLICE
This is a PyObject * that is a Python slice object.
.. sip-type:: SIP_PYTUPLE
This is a PyObject * that is a Python tuple object.
.. sip-type:: SIP_PYTYPE
This is a PyObject * that is a Python type object.
It is important to understand that a SIP specification describes the Python API, i.e. the API available to the Python programmer when they import the generated module. It does not have to accurately represent the underlying C/C++ library. There is nothing wrong with omitting functions that make little sense in a Python context, or adding functions implemented with handwritten code that have no C/C++ equivalent. It is even possible (and sometimes necessary) to specify a different super-class hierarchy for a C++ class. All that matters is that the generated code compiles properly.
In most cases the Python API matches the C/C++ API. In some cases handwritten code (see :directive:`%MethodCode`) is used to map from one to the other without SIP having to know the details itself. However, there are a few cases where SIP generates a thin wrapper around a C++ method or constructor (see :ref:`ref-derived-classes`) and needs to know the exact C++ signature. To deal with these cases SIP allows two signatures to be specified. For example:
class Klass { public: // The Python signature is a tuple, but the underlying C++ signature // is a 2 element array. Klass(SIP_PYTUPLE) [(int *)]; %MethodCode int iarr[2]; if (PyArg_ParseTuple(a0, "ii", &iarr[0], &iarr[1])) { // Note that we use the SIP generated derived class // constructor. Py_BEGIN_ALLOW_THREADS sipCpp = new sipKlass(iarr); Py_END_ALLOW_THREADS } %End }; SIP implements C++ namespaces as a Python class which cannot be instantiated. The contents of the namespace, including nested namespaces, are implemented as attributes of the class.
The namespace class is created in the module that SIP is parsing when it first sees the namespace defined. If a function (for example) is defined in a namespace that is first defined in another module then the function is added to the namespace class in that other module.
Say that we have a file a.sip that defines a module a_module as follows:
%Module a_module namespace N { void hello(); }; We also have a file b.sip that defines a module b_module as follows:
%Module b_module %Import a.sip namespace N { void bye(); }; When SIP parses b.sip it first sees the N namespace defined in module a_module. Therefore it places the bye() function in the N Python class in the a_module. It does not create an N Python class in the b_module. Consequently the following code will call the bye() function:
import a_module import b_module a_module.N.bye()
While this reflects the C++ usage it may not be obvious to the Python programmer who might expect to call the bye() function using:
import b_module b_module.N.bye()
In order to achieve this behavior make sure that the N namespace is first defined in the b_module. The following version of b.sip does this:
%Module b_module namespace N; %Import a.sip namespace N { void bye(); }; Alternatively you could just move the :directive:`%Import` directive so that it is at the end of the file.
