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GLib.VariantType

record (struct)

A type in the Variant type system.

Variant types are represented as strings, but have a strict syntax described below. All VariantTypes passed to GLib must be valid, and they are typically expected to be static (i.e. not provided by user input) as they determine how binary Variant data is interpreted.

To convert a static string to a VariantType in C, use the GLib.VARIANT_TYPE casting macro. When GLib is compiled with checks enabled, it will validate the type. To check if an arbitrary string is a valid VariantType, use VariantType.string_is_valid.

GVariant Type System

This section introduces the Variant type system. It is based, in large part, on the D-Bus type system, with two major changes and some minor lifting of restrictions. The D-Bus specification, therefore, provides a significant amount of information that is useful when working with Variant.

The first major change with respect to the D-Bus type system is the introduction of maybe (or ‘nullable’) types. Any type in Variant can be converted to a maybe type, in which case, nothing (or null) becomes a valid value. Maybe types have been added by introducing the character m to type strings.

The second major change is that the Variant type system supports the concept of ‘indefinite types’ — types that are less specific than the normal types found in D-Bus. For example, it is possible to speak of ‘an array of any type’ in Variant, where the D-Bus type system would require you to speak of ‘an array of integers’ or ‘an array of strings’. Indefinite types have been added by introducing the characters *, ? and r to type strings.

Finally, all arbitrary restrictions relating to the complexity of types are lifted along with the restriction that dictionary entries may only appear nested inside of arrays.

Just as in D-Bus, Variant types are described with strings (‘type strings’). Subject to the differences mentioned above, these strings are of the same form as those found in D-Bus. Note, however: D-Bus always works in terms of messages and therefore individual type strings appear nowhere in its interface. Instead, ‘signatures’ are a concatenation of the strings of the type of each argument in a message. Variant deals with single values directly so Variant type strings always describe the type of exactly one value. This means that a D-Bus signature string is generally not a valid Variant type string — except in the case that it is the signature of a message containing exactly one argument.

An indefinite type is similar in spirit to what may be called an abstract type in other type systems. No value can exist that has an indefinite type as its type, but values can exist that have types that are subtypes of indefinite types. That is to say, Variant.get_type will never return an indefinite type, but calling Variant.is_of_type with an indefinite type may return true. For example, you cannot have a value that represents ‘an array of no particular type’, but you can have an ‘array of integers’ which certainly matches the type of ‘an array of no particular type’, since ‘array of integers’ is a subtype of ‘array of no particular type’.

This is similar to how instances of abstract classes may not directly exist in other type systems, but instances of their non-abstract subtypes may. For example, in GTK, no object that has the type of GtkWidget can exist (since GtkWidget is an abstract class), but a GtkWindow can certainly be instantiated, and you would say that a GtkWindow is a GtkWidget (since GtkWindow is a subclass of GtkWidget).

Two types may not be compared by value; use VariantType.equal or VariantType.is_subtype_of May be copied using VariantType.copy and freed using VariantType.free.

GVariant Type Strings

A Variant type string can be any of the following:

  • any basic type string (listed below)
  • v, r or *
  • one of the characters a or m, followed by another type string
  • the character (, followed by a concatenation of zero or more other type strings, followed by the character )
  • the character {, followed by a basic type string (see below), followed by another type string, followed by the character }

A basic type string describes a basic type (as per VariantType.is_basic) and is always a single character in length. The valid basic type strings are b, y, n, q, i, u, x, t, h, d, s, o, g and ?.

The above definition is recursive to arbitrary depth. aaaaai and (ui(nq((y)))s) are both valid type strings, as is a(aa(ui)(qna{ya(yd)})). In order to not hit memory limits, Variant imposes a limit on recursion depth of 65 nested containers. This is the limit in the D-Bus specification (64) plus one to allow a GDBusMessage to be nested in a top-level tuple.

The meaning of each of the characters is as follows:

  • b: the type string of G_VARIANT_TYPE_BOOLEAN; a boolean value.
  • y: the type string of G_VARIANT_TYPE_BYTE; a byte.
  • n: the type string of G_VARIANT_TYPE_INT16; a signed 16 bit integer.
  • q: the type string of G_VARIANT_TYPE_UINT16; an unsigned 16 bit integer.
  • i: the type string of G_VARIANT_TYPE_INT32; a signed 32 bit integer.
  • u: the type string of G_VARIANT_TYPE_UINT32; an unsigned 32 bit integer.
  • x: the type string of G_VARIANT_TYPE_INT64; a signed 64 bit integer.
  • t: the type string of G_VARIANT_TYPE_UINT64; an unsigned 64 bit integer.
  • h: the type string of G_VARIANT_TYPE_HANDLE; a signed 32 bit value that, by convention, is used as an index into an array of file descriptors that are sent alongside a D-Bus message.
  • d: the type string of G_VARIANT_TYPE_DOUBLE; a double precision floating point value.
  • s: the type string of G_VARIANT_TYPE_STRING; a string.
  • o: the type string of G_VARIANT_TYPE_OBJECT_PATH; a string in the form of a D-Bus object path.
  • g: the type string of G_VARIANT_TYPE_SIGNATURE; a string in the form of a D-Bus type signature.
  • ?: the type string of G_VARIANT_TYPE_BASIC; an indefinite type that is a supertype of any of the basic types.
  • v: the type string of G_VARIANT_TYPE_VARIANT; a container type that contain any other type of value.
  • a: used as a prefix on another type string to mean an array of that type; the type string ai, for example, is the type of an array of signed 32-bit integers.
  • m: used as a prefix on another type string to mean a ‘maybe’, or ‘nullable’, version of that type; the type string ms, for example, is the type of a value that maybe contains a string, or maybe contains nothing.
  • (): used to enclose zero or more other concatenated type strings to create a tuple type; the type string (is), for example, is the type of a pair of an integer and a string.
  • r: the type string of G_VARIANT_TYPE_TUPLE; an indefinite type that is a supertype of any tuple type, regardless of the number of items.
  • {}: used to enclose a basic type string concatenated with another type string to create a dictionary entry type, which usually appears inside of an array to form a dictionary; the type string a{sd}, for example, is the type of a dictionary that maps strings to double precision floating point values.

The first type (the basic type) is the key type and the second type is the value type. The reason that the first type is restricted to being a basic type is so that it can easily be hashed. - *: the type string of G_VARIANT_TYPE_ANY; the indefinite type that is a supertype of all types. Note that, as with all type strings, this character represents exactly one type. It cannot be used inside of tuples to mean ‘any number of items’.

Any type string of a container that contains an indefinite type is, itself, an indefinite type. For example, the type string a* (corresponding to G_VARIANT_TYPE_ARRAY) is an indefinite type that is a supertype of every array type. (*s) is a supertype of all tuples that contain exactly two items where the second item is a string.

a{?*} is an indefinite type that is a supertype of all arrays containing dictionary entries where the key is any basic type and the value is any type at all. This is, by definition, a dictionary, so this type string corresponds to G_VARIANT_TYPE_DICTIONARY. Note that, due to the restriction that the key of a dictionary entry must be a basic type, {**} is not a valid type string.

Constructors

new

@classmethod
def new(cls, type_string: str) -> VariantType

Creates a new VariantType corresponding to the type string given by type_string.

It is appropriate to call VariantType.free on the return value.

It is a programmer error to call this function with an invalid type string. Use VariantType.string_is_valid if you are unsure.

Parameters:

  • type_string — a valid GVariant type string

new_array

@classmethod
def new_array(cls, element: VariantType) -> VariantType

Constructs the type corresponding to an array of elements of the type type.

It is appropriate to call VariantType.first on the return value.

Parameters:

  • element — an element type

new_dict_entry

@classmethod
def new_dict_entry(cls, key: VariantType, value: VariantType) -> VariantType

Constructs the type corresponding to a dictionary entry with a key of type key and a value of type value.

It is appropriate to call VariantType.free on the return value.

Parameters:

  • key — a basic type to use for the key
  • value — a type to use for the value

new_maybe

@classmethod
def new_maybe(cls, element: VariantType) -> VariantType

Constructs the type corresponding to a ‘maybe’ instance containing type type or Nothing.

It is appropriate to call VariantType.free on the return value.

Parameters:

  • element — an element type

new_tuple

@classmethod
def new_tuple(cls, items: list[VariantType]) -> VariantType

Constructs a new tuple type, from items.

length is the number of items in items, or -1 to indicate that items is NULL-terminated.

It is appropriate to call VariantType.free on the return value.

Parameters:

  • items — an array of types, one for each item

Methods

copy

def copy(self) -> VariantType

Makes a copy of a VariantType.

It is appropriate to call VariantType.free on the return value. type may not be NULL.

dup_string

def dup_string(self) -> str

Returns a newly-allocated copy of the type string corresponding to type.

The returned string is nul-terminated. It is appropriate to call free on the return value.

element

def element(self) -> VariantType

Determines the element type of an array or ‘maybe’ type.

This function may only be used with array or ‘maybe’ types.

equal

def equal(self, type2: VariantType) -> bool

Compares type1 and type2 for equality.

Only returns true if the types are exactly equal. Even if one type is an indefinite type and the other is a subtype of it, false will be returned if they are not exactly equal. If you want to check for subtypes, use VariantType.is_subtype_of.

The argument types of type1 and type2 are only gconstpointer to allow use with HashTable without function pointer casting. For both arguments, a valid VariantType must be provided.

Parameters:

  • type2 — another type to compare

first

def first(self) -> VariantType | None

Determines the first item type of a tuple or dictionary entry type.

This function may only be used with tuple or dictionary entry types, but must not be used with the generic tuple type G_VARIANT_TYPE_TUPLE.

In the case of a dictionary entry type, this returns the type of the key.

NULL is returned in case of type being G_VARIANT_TYPE_UNIT.

This call, together with VariantType.next provides an iterator interface over tuple and dictionary entry types.

free

def free(self) -> None

Frees a VariantType that was allocated with VariantType.copy, VariantType.new or one of the container type constructor functions.

In the case that type is NULL, this function does nothing.

Since 2.24

get_string_length

def get_string_length(self) -> int

Returns the length of the type string corresponding to the given type.

This function must be used to determine the valid extent of the memory region returned by VariantType.peek_string.

hash

def hash(self) -> int

Hashes type.

The argument type of type is only gconstpointer to allow use with HashTable without function pointer casting. A valid VariantType must be provided.

is_array

def is_array(self) -> bool

Determines if the given type is an array type.

This is true if the type string for type starts with an a.

This function returns true for any indefinite type for which every definite subtype is an array type — G_VARIANT_TYPE_ARRAY, for example.

is_basic

def is_basic(self) -> bool

Determines if the given type is a basic type.

Basic types are booleans, bytes, integers, doubles, strings, object paths and signatures.

Only a basic type may be used as the key of a dictionary entry.

This function returns FALSE for all indefinite types except G_VARIANT_TYPE_BASIC.

is_container

def is_container(self) -> bool

Determines if the given type is a container type.

Container types are any array, maybe, tuple, or dictionary entry types plus the variant type.

This function returns true for any indefinite type for which every definite subtype is a container — G_VARIANT_TYPE_ARRAY, for example.

is_definite

def is_definite(self) -> bool

Determines if the given type is definite (ie: not indefinite).

A type is definite if its type string does not contain any indefinite type characters (*, ?, or r).

A Variant instance may not have an indefinite type, so calling this function on the result of Variant.get_type will always result in true being returned. Calling this function on an indefinite type like G_VARIANT_TYPE_ARRAY, however, will result in FALSE being returned.

is_dict_entry

def is_dict_entry(self) -> bool

Determines if the given type is a dictionary entry type.

This is true if the type string for type starts with a {.

This function returns true for any indefinite type for which every definite subtype is a dictionary entry type — G_VARIANT_TYPE_DICT_ENTRY, for example.

is_maybe

def is_maybe(self) -> bool

Determines if the given type is a ‘maybe’ type.

This is true if the type string for type starts with an m.

This function returns true for any indefinite type for which every definite subtype is a ‘maybe’ type — G_VARIANT_TYPE_MAYBE, for example.

is_subtype_of

def is_subtype_of(self, supertype: VariantType) -> bool

Checks if type is a subtype of supertype.

This function returns true if type is a subtype of supertype. All types are considered to be subtypes of themselves. Aside from that, only indefinite types can have subtypes.

Parameters:

  • supertype — type of potential supertype

is_tuple

def is_tuple(self) -> bool

Determines if the given type is a tuple type.

This is true if the type string for type starts with a ( or if type is G_VARIANT_TYPE_TUPLE.

This function returns true for any indefinite type for which every definite subtype is a tuple type — G_VARIANT_TYPE_TUPLE, for example.

is_variant

def is_variant(self) -> bool

Determines if the given type is the variant type.

key

def key(self) -> VariantType

Determines the key type of a dictionary entry type.

This function may only be used with a dictionary entry type. Other than the additional restriction, this call is equivalent to VariantType.first.

n_items

def n_items(self) -> int

Determines the number of items contained in a tuple or dictionary entry type.

This function may only be used with tuple or dictionary entry types, but must not be used with the generic tuple type G_VARIANT_TYPE_TUPLE.

In the case of a dictionary entry type, this function will always return 2.

next

def next(self) -> VariantType | None

Determines the next item type of a tuple or dictionary entry type.

type must be the result of a previous call to VariantType.first or VariantType.next.

If called on the key type of a dictionary entry then this call returns the value type. If called on the value type of a dictionary entry then this call returns NULL.

For tuples, NULL is returned when type is the last item in the tuple.

value

def value(self) -> VariantType

Determines the value type of a dictionary entry type.

This function may only be used with a dictionary entry type.

Static functions

checked_

@staticmethod
def checked_(type_string: str) -> VariantType

string_get_depth_

@staticmethod
def string_get_depth_(type_string: str) -> int

string_is_valid

@staticmethod
def string_is_valid(type_string: str) -> bool

Checks if type_string is a valid GVariant type string.

This call is equivalent to calling VariantType.string_scan and confirming that the following character is a nul terminator.

Parameters:

  • type_string — a pointer to any string

string_scan

@staticmethod
def string_scan(string: str, limit: str | None = ...) -> tuple[bool, str]

Scan for a single complete and valid GVariant type string in string.

The memory pointed to by limit (or bytes beyond it) is never accessed.

If a valid type string is found, endptr is updated to point to the first character past the end of the string that was found and True is returned.

If there is no valid type string starting at string, or if the type string does not end before limit then False is returned.

For the simple case of checking if a string is a valid type string, see VariantType.string_is_valid.

Parameters:

  • string — a pointer to any string
  • limit — the end of string