VariantType

Added in version 2.24.

class VariantType(**kwargs)

A type in the Variant 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, get_type will never return an indefinite type, but calling 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 <https://docs.gtk.org/gtk4/class.Widget.html>`_ can exist (since GtkWidget is an abstract class), but a `GtkWindow <https://docs.gtk.org/gtk4/class.Window.html>`_ 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 equal or is_subtype_of May be copied using copy and freed using 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 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 <../gio/class.DBusMessage.html>`_ 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

class VariantType

classmethod new(type_string: str) → VariantType

Creates a new VariantType corresponding to the type string given by type_string. It is appropriate to call free() on the return value.

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

Added in version 2.24.

Parameters:

type_string – a valid GVariant type string

classmethod new_array(element: VariantType) → VariantType

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

It is appropriate to call free() on the return value.

Parameters:

element – a VariantType

classmethod new_dict_entry(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 free() on the return value.

Parameters:

• key – a basic VariantType

• value – a VariantType

classmethod new_maybe(element: VariantType) → VariantType

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

It is appropriate to call free() on the return value.

Parameters:

element – a VariantType

classmethod new_tuple(items: Sequence[VariantType]) → VariantType

Constructs a new tuple type, from items.

length is the number of items in items, or -1 to indicate that items is None-terminated.

It is appropriate to call free() on the return value.

Parameters:

items – an array of VariantType, one for each item

Methods

class VariantType

checked_(type_string: str) → VariantType

Parameters:

type_string

dup_string() → 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() → VariantType

Determines the element type of an array or maybe type.

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

equal(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 is_subtype_of().

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

Parameters:

type2 – a VariantType

first() → VariantType

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.

None is returned in case of type being %G_VARIANT_TYPE_UNIT.

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

free() → None

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

In the case that type is None, this function does nothing.

Since 2.24

get_string_length() → 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 peek_string().

hash() → int

Hashes type.

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

is_array() → 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() → 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() → 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() → 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 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() → 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() → 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(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 – a VariantType

is_tuple() → 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() → bool

Determines if the given type is the variant type.

key() → 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 first().

n_items() → 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() → VariantType

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

type must be the result of a previous call to first() or 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 None.

For tuples, None is returned when type is the last item in a tuple.

string_get_depth_(type_string: str) → int

Parameters:

type_string

string_is_valid(type_string: str) → bool

Checks if type_string is a valid GVariant type string. This call is equivalent to calling string_scan() and confirming that the following character is a nul terminator.

Parameters:

type_string – a pointer to any string

string_scan(string: str, limit: str | None = 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 string_is_valid().

Added in version 2.24.

Parameters:

• string – a pointer to any string

• limit – the end of string, or None

value() → VariantType

Determines the value type of a dictionary entry type.

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