Annotations

In this section we describe each of the annotations that can be used in specification files.

Annotations can either be argument annotations, class annotations, mapped type annotations, enum annotations, exception annotations, function annotations, license annotations, typedef annotations or variable annotations depending on the context in which they can be used.

Annotations are placed between forward slashes (/). Multiple annotations are comma separated within the slashes.

Annotations have a type and, possibly, a value. The type determines the format of the value. The name of an annotation and its value are separated by =.

Annotations can have one of the following types:

boolean

This type of annotation has no value and is implicitly true.

name

The value is a name that is compatible with a C/C++ identifier. In some cases the value is optional.

dotted name

The value is a name that is compatible with an identifier preceded by a Python scope.

string

The value is a double quoted string.

API range

The value is the name of an API (defined using the %API directive) separated by a range of version numbers with a colon.

The range of version numbers is a pair of numbers separated by a hyphen specifying the lower and upper bounds of the range. A version number is within the range if it is greater or equal to the lower bound and less than the upper bound. Each bound can be omitted meaning that the range is unbounded in that direction.

For example:

# This is part of the PyQt4 API up to but excluding v2.
void hex() /API=PyQt4:-2/

# This is part of the PyQt4 API starting from v2.
void hex() /PyName=hex_, API=PyQt4:2-/

The following example shows argument and function annotations:

void exec(QWidget * /Transfer/) /ReleaseGIL, PyName=call_exec/;

Note that the current version of SIP does not complain about unknown annotations, or annotations used out of their correct context.

Argument Annotations

AllowNone

This boolean annotation specifies that the value of the corresponding argument (which should be either SIP_PYCALLABLE, SIP_PYDICT, SIP_PYLIST, SIP_PYSLICE, SIP_PYTUPLE or SIP_PYTYPE) may be None.

Array

This boolean annotation specifies that the corresponding argument refers to an array.

The argument should be either a pointer to a wrapped type, a char * or a unsigned char *. If the argument is a character array then the annotation also implies the Encoding annotation with an encoding of "None".

There must be a corresponding argument with the ArraySize annotation specified. The annotation may only be specified once in a list of arguments.

ArraySize

This boolean annotation specifies that the corresponding argument (which should be either short, unsigned short, int, unsigned, long or unsigned long) refers to the size of an array. There must be a corresponding argument with the Array annotation specified. The annotation may only be specified once in a list of arguments.

Constrained

Python will automatically convert between certain compatible types. For example, if a floating pointer number is expected and an integer supplied, then the integer will be converted appropriately. This can cause problems when wrapping C or C++ functions with similar signatures. For example:

// The wrapper for this function will also accept an integer argument
// which Python will automatically convert to a floating point number.
void foo(double);

// The wrapper for this function will never get used.
void foo(int);

This boolean annotation specifies that the corresponding argument (which should be either bool, int, float, double, enum or a wrapped class) must match the type without any automatic conversions. In the context of a wrapped class the invocation of any %ConvertToTypeCode is suppressed.

The following example gets around the above problem:

// The wrapper for this function will only accept floating point
// numbers.
void foo(double /Constrained/);

// The wrapper for this function will be used for anything that Python
// can convert to an integer, except for floating point numbers.
void foo(int);

Encoding

This string annotation specifies that the corresponding argument (which should be either char, const char, char * or const char *) refers to an encoded character or '\0' terminated encoded string with the specified encoding. The encoding can be either "ASCII", "Latin-1", "UTF-8" or "None". An encoding of "None" means that the corresponding argument refers to an unencoded character or string.

The default encoding is specified by the %DefaultEncoding directive. If the directive is not specified then None is used.

Python v3 will use the bytes type to represent the argument if the encoding is "None" and the str type otherwise.

Python v2 will use the str type to represent the argument if the encoding is "None" and the unicode type otherwise.

GetWrapper

This boolean annotation is only ever used in conjunction with handwritten code specified with the %MethodCode directive. It causes an extra variable to be generated for the corresponding argument which is a pointer to the Python object that wraps the argument.

See the %MethodCode directive for more detail.

In

This boolean annotation is used to specify that the corresponding argument (which should be a pointer type) is used to pass a value to the function.

For pointers to wrapped C structures or C++ class instances, char * and unsigned char * then this annotation is assumed unless the Out annotation is specified.

For pointers to other types then this annotation must be explicitly specified if required. The argument will be dereferenced to obtain the actual value.

Both In and Out may be specified for the same argument.

KeepReference

This boolean annotation is used to specify that a reference to the corresponding argument should be kept to ensure that the object is not garbage collected. If the method is called again with a new argument then the reference to the previous argument is discarded. Note that ownership of the argument is not changed.

Out

This boolean annotation is used to specify that the corresponding argument (which should be a pointer type) is used by the function to return a value as an element of a tuple.

For pointers to wrapped C structures or C++ class instances, char * and unsigned char * then this annotation must be explicitly specified if required.

For pointers to other types then this annotation is assumed unless the In annotation is specified.

Both In and Out may be specified for the same argument.

ResultSize

This boolean annotation is used with functions or methods that return a void * or const void *. It identifies an argument that defines the size of the block of memory whose address is being returned. This allows the sip.voidptr object that wraps the address to support the Python buffer protocol and allows the memory to be read and updated when wrapped by the Python buffer() builtin.

SingleShot

This boolean annotation is used only with arguments of type SIP_RXOBJ_CON to specify that the signal connected to the slot will only ever be emitted once. This prevents a certain class of memory leaks.

Transfer

This boolean annotation is used to specify that ownership of the corresponding argument (which should be a wrapped C structure or C++ class instance) is transferred from Python to C++. In addition, if the argument is of a class method, then it is associated with the class instance with regard to the cyclic garbage collector.

See Ownership of Objects for more detail.

TransferBack

This boolean annotation is used to specify that ownership of the corresponding argument (which should be a wrapped C structure or C++ class instance) is transferred back to Python from C++. In addition, any association of the argument with regard to the cyclic garbage collector with another instance is removed.

See Ownership of Objects for more detail.

TransferThis

This boolean annotation is only used in C++ constructors or methods. In the context of a constructor or factory method it specifies that ownership of the instance being created is transferred from Python to C++ if the corresponding argument (which should be a wrapped C structure or C++ class instance) is not None. In addition, the newly created instance is associated with the argument with regard to the cyclic garbage collector.

In the context of a non-factory method it specifies that ownership of this is transferred from Python to C++ if the corresponding argument is not None. If it is None then ownership is transferred to Python.

The annotation may be used more that once, in which case ownership is transferred to last instance that is not None.

See Ownership of Objects for more detail.

Class Annotations

Abstract

This boolean annotation is used to specify that the class has additional pure virtual methods that have not been specified and so it cannot be instantiated or sub-classed from Python.

AllowNone

New in version 4.8.2.

Normally when a Python object is converted to a C/C++ instance None is handled automatically before the class’s %ConvertToTypeCode is called. This boolean annotation specifies that the handling of None will be left to the %ConvertToTypeCode. The annotation is ignored if the class does not have any %ConvertToTypeCode.

API

New in version 4.9.

This API range annotation is used to specify an API and corresponding range of version numbers that the class is enabled for.

If a class or mapped type has different implementations enabled for different ranges of version numbers then those ranges must not overlap.

See Managing Incompatible APIs for more detail.

DelayDtor

This boolean annotation is used to specify that the class’s destructor should not be called until the Python interpreter exits. It would normally only be applied to singleton classes.

When the Python interpreter exits the order in which any wrapped instances are garbage collected is unpredictable. However, the underlying C or C++ instances may need to be destroyed in a certain order. If this annotation is specified then when the wrapped instance is garbage collected the C or C++ instance is not destroyed but instead added to a list of delayed instances. When the interpreter exits then the function sipDelayedDtors() is called with the list of delayed instances. sipDelayedDtors() can then choose to call (or ignore) the destructors in any desired order.

The sipDelayedDtors() function must be specified using the %ModuleCode directive.

void sipDelayedDtors(const sipDelayedDtor *dd_list)

Parameter:dd_list – the linked list of delayed instances.

sipDelayedDtor

This structure describes a particular delayed destructor.

const char *dd_name

This is the name of the class excluding any package or module name.

void *dd_ptr

This is the address of the C or C++ instance to be destroyed. It’s exact type depends on the value of dd_isderived.

int dd_isderived

This is non-zero if the type of dd_ptr is actually the generated derived class. This allows the correct destructor to be called. See Generated Derived Classes.

sipDelayedDtor *dd_next

This is the address of the next entry in the list or zero if this is the last one.

Note that the above applies only to C and C++ instances that are owned by Python.

Deprecated

This boolean annotation is used to specify that the class is deprecated. It is the equivalent of annotating all the class’s constructors, function and methods as being deprecated.

External

This boolean annotation is used to specify that the class is defined in another module. Declarations of external classes are private to the module in which they appear.

Metatype

This dotted name annotation specifies the name of the Python type object (i.e. the value of the tp_name field) used as the meta-type used when creating the type object for this C structure or C++ type.

See the section Types and Meta-types for more details.

NoDefaultCtors

This boolean annotation is used to suppress the automatic generation of default constructors for the class.

PyName

This name annotation specifies an alternative name for the class being wrapped which is used when it is referred to from Python. It is required when a class name is the same as a Python keyword. It may also be used to avoid name clashes with other objects (e.g. enums, exceptions, functions) that have the same name in the same C++ scope.

Supertype

This dotted name annotation specifies the name of the Python type object (i.e. the value of the tp_name field) used as the super-type used when creating the type object for this C structure or C++ type.

See the section Types and Meta-types for more details.

Mapped Type Annotations

AllowNone

Normally when a Python object is converted to a C/C++ instance None is handled automatically before the mapped type’s %ConvertToTypeCode is called. This boolean annotation specifies that the handling of None will be left to the %ConvertToTypeCode.

API

New in version 4.9.

This API range annotation is used to specify an API and corresponding range of version numbers that the mapped type is enabled for.

If a class or mapped type has different implementations enabled for different ranges of version numbers then those ranges must not overlap.

See Managing Incompatible APIs for more detail.

NoRelease

This boolean annotation is used to specify that the mapped type does not support the sipReleaseType() function. Any %ConvertToTypeCode should not create temporary instances of the mapped type, i.e. it should not return SIP_TEMPORARY.

Enum Annotations

PyName

This name annotation specifies an alternative name for the enum or enum member being wrapped which is used when it is referred to from Python. It is required when an enum or enum member name is the same as a Python keyword. It may also be used to avoid name clashes with other objects (e.g. classes, exceptions, functions) that have the same name in the same C++ scope.

Exception Annotations

PyName

This name annotation specifies an alternative name for the exception being defined which is used when it is referred to from Python. It is required when an exception name is the same as a Python keyword. It may also be used to avoid name clashes with other objects (e.g. classes, enums, functions) that have the same name.

Function Annotations

API

New in version 4.9.

This API range annotation is used to specify an API and corresponding range of version numbers that the function is enabled for.

See Managing Incompatible APIs for more detail.

AutoGen

This optional name annotation is used with class methods to specify that the method be automatically included in all sub-classes. The value is the name of a feature (specified using the %Feature directive) which must be enabled for the method to be generated.

Default

This boolean annotation is only used with C++ constructors. Sometimes SIP needs to create a class instance. By default it uses a constructor with no compulsory arguments if one is specified. (SIP will automatically generate a constructor with no arguments if no constructors are specified.) This annotation is used to explicitly specify which constructor to use. Zero is passed as the value of any arguments to the constructor.

Deprecated

This boolean annotation is used to specify that the constructor or function is deprecated. A deprecation warning is issued whenever the constructor or function is called.

Factory

This boolean annotation specifies that the value returned by the function (which should be a wrapped C structure or C++ class instance) is a newly created instance and is owned by Python.

See Ownership of Objects for more detail.

HoldGIL

This boolean annotation specifies that the Python Global Interpreter Lock (GIL) is not released before the call to the underlying C or C++ function. See The Python Global Interpreter Lock and the ReleaseGIL annotation.

NewThread

This boolean annotation specifies that the function will create a new thread.

NoArgParser

This boolean annotation is used with methods and global functions to specify that the supplied %MethodCode will handle the parsing of the arguments.

NoDerived

This boolean annotation is only used with C++ constructors. In many cases SIP generates a derived class for each class being wrapped (see Generated Derived Classes). This derived class contains constructors with the same C++ signatures as the class being wrapped. Sometimes you may want to define a Python constructor that has no corresponding C++ constructor. This annotation is used to suppress the generation of the constructor in the derived class.

Numeric

This boolean annotation specifies that the operator should be interpreted as a numeric operator rather than a sequence operator. Python uses the + operator for adding numbers and concatanating sequences, and the * operator for multiplying numbers and repeating sequences. SIP tries to work out which is meant by looking at other operators that have been defined for the type. If it finds either -, -=, /, /=, % or %= defined then it assumes that +, +=, * and *= should be numeric operators. Otherwise, if it finds either [], __getitem__(), __setitem__() or __delitem__() defined then it assumes that they should be sequence operators. This annotation is used to force SIP to treat the operator as numeric.

PostHook

This name annotation is used to specify the name of a Python builtin that is called immediately after the call to the underlying C or C++ function or any handwritten code. The builtin is not called if an error occurred. It is primarily used to integrate with debuggers.

PreHook

This name annotation is used to specify the name of a Python builtin that is called immediately after the function’s arguments have been successfully parsed and before the call to the underlying C or C++ function or any handwritten code. It is primarily used to integrate with debuggers.

PyName

This name annotation specifies an alternative name for the function being wrapped which is used when it is referred to from Python. It is required when a function or method name is the same as a Python keyword. It may also be used to avoid name clashes with other objects (e.g. classes, enums, exceptions) that have the same name in the same C++ scope.

ReleaseGIL

This boolean annotation specifies that the Python Global Interpreter Lock (GIL) is released before the call to the underlying C or C++ function and reacquired afterwards. It should be used for functions that might block or take a significant amount of time to execute. See The Python Global Interpreter Lock and the HoldGIL annotation.

Transfer

This boolean annotation specifies that ownership of the value returned by the function (which should be a wrapped C structure or C++ class instance) is transferred to C++. It is only used in the context of a class constructor or a method.

In the case of methods returned values (unless they are new references to already wrapped values) are normally owned by C++ anyway. However, in addition, an association between the returned value and the instance containing the method is created with regard to the cyclic garbage collector.

See Ownership of Objects for more detail.

TransferBack

This boolean annotation specifies that ownership of the value returned by the function (which should be a wrapped C structure or C++ class instance) is transferred back to Python from C++. Normally returned values (unless they are new references to already wrapped values) are owned by C++. In addition, any association of the returned value with regard to the cyclic garbage collector with another instance is removed.

See Ownership of Objects for more detail.

TransferThis

This boolean annotation specifies that ownership of this is transferred from Python to C++.

See Ownership of Objects for more detail.

License Annotations

Licensee

This optional string annotation specifies the license’s licensee. No restrictions are placed on the contents of the string.

See the %License directive.

Signature

This optional string annotation specifies the license’s signature. No restrictions are placed on the contents of the string.

See the %License directive.

Timestamp

This optional string annotation specifies the license’s timestamp. No restrictions are placed on the contents of the string.

See the %License directive.

Type

This string annotation specifies the license’s type. No restrictions are placed on the contents of the string.

See the %License directive.

Typedef Annotations

NoTypeName

This boolean annotation specifies that the definition of the type rather than the name of the type being defined should be used in the generated code.

Normally a typedef would be defined as follows:

typedef bool MyBool;

This would result in MyBool being used in the generated code.

Specifying the annotation means that bool will be used in the generated code instead.

Variable Annotations

PyName

This name annotation specifies an alternative name for the variable being wrapped which is used when it is referred to from Python. It is required when a variable name is the same as a Python keyword. It may also be used to avoid name clashes with other objects (e.g. classes, functions) that have the same name in the same C++ scope.