GLib.VariantType

Fields

None

Methods

class checked_ (arg0)
class new (type_string)
class new_array (element)
class new_dict_entry (key, value)
class new_maybe (element)
class new_tuple (items)
class string_get_depth_ (type_string)
class string_is_valid (type_string)
class string_scan (string, limit)
  copy ()
  dup_string ()
  element ()
  equal (type2)
  first ()
  free ()
  get_string_length ()
  hash ()
  is_array ()
  is_basic ()
  is_container ()
  is_definite ()
  is_dict_entry ()
  is_maybe ()
  is_subtype_of (supertype)
  is_tuple ()
  is_variant ()
  key ()
  n_items ()
  next ()
  value ()

Details

class GLib.VariantType

This section introduces the GLib.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 GLib.Variant.

The first major change with respect to the D-Bus type system is the introduction of maybe (or “nullable”) types. Any type in GLib.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 GLib.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 GLib.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, GLib.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 DBus. 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. GLib.Variant deals with single values directly so GLib.Variant type strings always describe the type of exactly one value. This means that a D-Bus signature string is generally not a valid GLib.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, GLib.Variant.get_type() will never return an indefinite type, but calling GLib.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 #GtkBin can exist (since #GtkBin is an abstract class), but a #GtkWindow can certainly be instantiated, and you would say that the #GtkWindow is a #GtkBin (since #GtkWindow is a subclass of #GtkBin).

GLib.Variant Type Strings

A GLib.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 GLib.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, GLib.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.

classmethod checked_(arg0)[source]
Parameters:arg0 (str) –
Return type:GLib.VariantType
classmethod new(type_string)[source]
Parameters:type_string (str) – a valid GLib.Variant type string
Returns:a new GLib.VariantType
Return type:GLib.VariantType

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

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

New in version 2.24.

classmethod new_array(element)[source]
Parameters:element (GLib.VariantType) – a GLib.VariantType
Returns:a new array GLib.VariantType
Return type:GLib.VariantType

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

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

classmethod new_dict_entry(key, value)[source]
Parameters:
Returns:

a new dictionary entry GLib.VariantType

Return type:

GLib.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 GLib.VariantType.free() on the return value.

classmethod new_maybe(element)[source]
Parameters:element (GLib.VariantType) – a GLib.VariantType
Returns:a new maybe GLib.VariantType
Return type:GLib.VariantType

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

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

classmethod new_tuple(items)[source]
Parameters:items ([GLib.VariantType]) – an array of GLib.VariantTypes, one for each item
Returns:a new tuple GLib.VariantType
Return type:GLib.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 GLib.VariantType.free() on the return value.

classmethod string_get_depth_(type_string)[source]
Parameters:type_string (str) –
Return type:int
classmethod string_is_valid(type_string)[source]
Parameters:type_string (str) – a pointer to any string
Returns:True if type_string is exactly one valid type string
Return type:bool

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

classmethod string_scan(string, limit)[source]
Parameters:
  • string (str) – a pointer to any string
  • limit (str or None) – the end of string, or None
Returns:

True if a valid type string was found

endptr:location to store the end pointer, or None

Return type:

(bool, endptr: str)

Scan for a single complete and valid GLib.Variant 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 GLib.VariantType.string_is_valid().

New in version 2.24.

copy()[source]
Returns:a new GLib.VariantType
Return type:GLib.VariantType

Makes a copy of a GLib.VariantType. It is appropriate to call GLib.VariantType.free() on the return value. self may not be None.

dup_string()[source]
Returns:the corresponding type string
Return type:str

Returns a newly-allocated copy of the type string corresponding to self. The returned string is nul-terminated. It is appropriate to call GLib.free() on the return value.

element()[source]
Returns:the element type of self
Return type:GLib.VariantType

Determines the element type of an array or maybe type.

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

equal(type2)[source]
Parameters:type2 (GLib.VariantType) – a GLib.VariantType
Returns:True if self and type2 are exactly equal
Return type:bool

Compares self 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 GLib.VariantType.is_subtype_of().

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

first()[source]
Returns:the first item type of self, or None
Return type:GLib.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 self being %G_VARIANT_TYPE_UNIT.

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

free()[source]

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

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

New in version 2.24.

get_string_length()[source]
Returns:the length of the corresponding type string
Return type:int

Returns the length of the type string corresponding to the given self. This function must be used to determine the valid extent of the memory region returned by g_variant_type_peek_string().

hash()[source]
Returns:the hash value
Return type:int

Hashes self.

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

is_array()[source]
Returns:True if self is an array type
Return type:bool

Determines if the given self is an array type. This is true if the type string for self 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()[source]
Returns:True if self is a basic type
Return type:bool

Determines if the given self 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()[source]
Returns:True if self is a container type
Return type:bool

Determines if the given self 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()[source]
Returns:True if self is definite
Return type:bool

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

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

A GLib.Variant instance may not have an indefinite type, so calling this function on the result of GLib.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()[source]
Returns:True if self is a dictionary entry type
Return type:bool

Determines if the given self is a dictionary entry type. This is true if the type string for self 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()[source]
Returns:True if self is a maybe type
Return type:bool

Determines if the given self is a maybe type. This is true if the type string for self 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)[source]
Parameters:supertype (GLib.VariantType) – a GLib.VariantType
Returns:True if self is a subtype of supertype
Return type:bool

Checks if self is a subtype of supertype.

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

is_tuple()[source]
Returns:True if self is a tuple type
Return type:bool

Determines if the given self is a tuple type. This is true if the type string for self starts with a ‘(‘ or if self 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()[source]
Returns:True if self is the variant type
Return type:bool

Determines if the given self is the variant type.

key()[source]
Returns:the key type of the dictionary entry
Return type:GLib.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 GLib.VariantType.first().

n_items()[source]
Returns:the number of items in self
Return type: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()[source]
Returns:the next GLib.VariantType after self, or None
Return type:GLib.VariantType

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

self must be the result of a previous call to GLib.VariantType.first() or GLib.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 None.

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

value()[source]
Returns:the value type of the dictionary entry
Return type:GLib.VariantType

Determines the value type of a dictionary entry type.

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