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GLib.Variant

record (struct)

GVariant is a variant datatype; it can contain one or more values along with information about the type of the values.

A GVariant may contain simple types, like an integer, or a boolean value; or complex types, like an array of two strings, or a dictionary of key value pairs. A GVariant is also immutable: once it’s been created neither its type nor its content can be modified further.

GVariant is useful whenever data needs to be serialized, for example when sending method parameters in D-Bus, or when saving settings using GSettings.

When creating a new GVariant, you pass the data you want to store in it along with a string representing the type of data you wish to pass to it.

For instance, if you want to create a GVariant holding an integer value you can use:

GVariant *v = g_variant_new ("u", 40);

The string u in the first argument tells GVariant that the data passed to the constructor (40) is going to be an unsigned integer.

More advanced examples of GVariant in use can be found in documentation for GVariant format strings.

The range of possible values is determined by the type.

The type system used by GVariant is VariantType.

GVariant instances always have a type and a value (which are given at construction time). The type and value of a GVariant instance can never change other than by the GVariant itself being destroyed. A GVariant cannot contain a pointer.

GVariant is reference counted using Variant.ref and Variant.unref. GVariant also has floating reference counts — see Variant.ref_sink.

GVariant is completely threadsafe. A GVariant instance can be concurrently accessed in any way from any number of threads without problems.

GVariant is heavily optimised for dealing with data in serialized form. It works particularly well with data located in memory-mapped files. It can perform nearly all deserialization operations in a small constant time, usually touching only a single memory page. Serialized GVariant data can also be sent over the network.

GVariant is largely compatible with D-Bus. Almost all types of GVariant instances can be sent over D-Bus. See VariantType for exceptions. (However, GVariant’s serialization format is not the same as the serialization format of a D-Bus message body: use GDBusMessage, in the GIO library, for those.)

For space-efficiency, the GVariant serialization format does not automatically include the variant’s length, type or endianness, which must either be implied from context (such as knowledge that a particular file format always contains a little-endian G_VARIANT_TYPE_VARIANT which occupies the whole length of the file) or supplied out-of-band (for instance, a length, type and/or endianness indicator could be placed at the beginning of a file, network message or network stream).

A GVariant’s size is limited mainly by any lower level operating system constraints, such as the number of bits in gsize. For example, it is reasonable to have a 2GB file mapped into memory with MappedFile, and call Variant.new_from_data on it.

For convenience to C programmers, GVariant features powerful varargs-based value construction and destruction. This feature is designed to be embedded in other libraries.

There is a Python-inspired text language for describing GVariant values. GVariant includes a printer for this language and a parser with type inferencing.

Memory Use

GVariant tries to be quite efficient with respect to memory use. This section gives a rough idea of how much memory is used by the current implementation. The information here is subject to change in the future.

The memory allocated by GVariant can be grouped into 4 broad purposes: memory for serialized data, memory for the type information cache, buffer management memory and memory for the GVariant structure itself.

Serialized Data Memory

This is the memory that is used for storing GVariant data in serialized form. This is what would be sent over the network or what would end up on disk, not counting any indicator of the endianness, or of the length or type of the top-level variant.

The amount of memory required to store a boolean is 1 byte. 16, 32 and 64 bit integers and double precision floating point numbers use their ‘natural’ size. Strings (including object path and signature strings) are stored with a nul terminator, and as such use the length of the string plus 1 byte.

‘Maybe’ types use no space at all to represent the null value and use the same amount of space (sometimes plus one byte) as the equivalent non-maybe-typed value to represent the non-null case.

Arrays use the amount of space required to store each of their members, concatenated. Additionally, if the items stored in an array are not of a fixed-size (ie: strings, other arrays, etc) then an additional framing offset is stored for each item. The size of this offset is either 1, 2 or 4 bytes depending on the overall size of the container. Additionally, extra padding bytes are added as required for alignment of child values.

Tuples (including dictionary entries) use the amount of space required to store each of their members, concatenated, plus one framing offset (as per arrays) for each non-fixed-sized item in the tuple, except for the last one. Additionally, extra padding bytes are added as required for alignment of child values.

Variants use the same amount of space as the item inside of the variant, plus 1 byte, plus the length of the type string for the item inside the variant.

As an example, consider a dictionary mapping strings to variants. In the case that the dictionary is empty, 0 bytes are required for the serialization.

If we add an item ‘width’ that maps to the int32 value of 500 then we will use 4 bytes to store the int32 (so 6 for the variant containing it) and 6 bytes for the string. The variant must be aligned to 8 after the 6 bytes of the string, so that’s 2 extra bytes. 6 (string) + 2 (padding) + 6 (variant) is 14 bytes used for the dictionary entry. An additional 1 byte is added to the array as a framing offset making a total of 15 bytes.

If we add another entry, ‘title’ that maps to a nullable string that happens to have a value of null, then we use 0 bytes for the null value (and 3 bytes for the variant to contain it along with its type string) plus 6 bytes for the string. Again, we need 2 padding bytes. That makes a total of 6 + 2 + 3 = 11 bytes.

We now require extra padding between the two items in the array. After the 14 bytes of the first item, that’s 2 bytes required. We now require 2 framing offsets for an extra two bytes. 14 + 2 + 11 + 2 = 29 bytes to encode the entire two-item dictionary.

Type Information Cache

For each GVariant type that currently exists in the program a type information structure is kept in the type information cache. The type information structure is required for rapid deserialization.

Continuing with the above example, if a GVariant exists with the type a{sv} then a type information struct will exist for a{sv}, {sv}, s, and v. Multiple uses of the same type will share the same type information. Additionally, all single-digit types are stored in read-only static memory and do not contribute to the writable memory footprint of a program using GVariant.

Aside from the type information structures stored in read-only memory, there are two forms of type information. One is used for container types where there is a single element type: arrays and maybe types. The other is used for container types where there are multiple element types: tuples and dictionary entries.

Array type info structures are 6 * sizeof (void *), plus the memory required to store the type string itself. This means that on 32-bit systems, the cache entry for a{sv} would require 30 bytes of memory (plus allocation overhead).

Tuple type info structures are 6 * sizeof (void *), plus 4 * sizeof (void *) for each item in the tuple, plus the memory required to store the type string itself. A 2-item tuple, for example, would have a type information structure that consumed writable memory in the size of 14 * sizeof (void *) (plus type string) This means that on 32-bit systems, the cache entry for {sv} would require 61 bytes of memory (plus allocation overhead).

This means that in total, for our a{sv} example, 91 bytes of type information would be allocated.

The type information cache, additionally, uses a HashTable to store and look up the cached items and stores a pointer to this hash table in static storage. The hash table is freed when there are zero items in the type cache.

Although these sizes may seem large it is important to remember that a program will probably only have a very small number of different types of values in it and that only one type information structure is required for many different values of the same type.

Buffer Management Memory

GVariant uses an internal buffer management structure to deal with the various different possible sources of serialized data that it uses. The buffer is responsible for ensuring that the correct call is made when the data is no longer in use by GVariant. This may involve a free or even MappedFile.unref.

One buffer management structure is used for each chunk of serialized data. The size of the buffer management structure is 4 * (void *). On 32-bit systems, that’s 16 bytes.

GVariant structure

The size of a GVariant structure is 6 * (void *). On 32-bit systems, that’s 24 bytes.

GVariant structures only exist if they are explicitly created with API calls. For example, if a GVariant is constructed out of serialized data for the example given above (with the dictionary) then although there are 9 individual values that comprise the entire dictionary (two keys, two values, two variants containing the values, two dictionary entries, plus the dictionary itself), only 1 GVariant instance exists — the one referring to the dictionary.

If calls are made to start accessing the other values then GVariant instances will exist for those values only for as long as they are in use (ie: until you call Variant.unref). The type information is shared. The serialized data and the buffer management structure for that serialized data is shared by the child.

Summary

To put the entire example together, for our dictionary mapping strings to variants (with two entries, as given above), we are using 91 bytes of memory for type information, 29 bytes of memory for the serialized data, 16 bytes for buffer management and 24 bytes for the GVariant instance, or a total of 160 bytes, plus allocation overhead. If we were to use Variant.get_child_value to access the two dictionary entries, we would use an additional 48 bytes. If we were to have other dictionaries of the same type, we would use more memory for the serialized data and buffer management for those dictionaries, but the type information would be shared.

Constructors

new_array

@classmethod
def new_array(cls, child_type: VariantType | None = ..., children: list[Variant] | None = ...) -> Variant

Creates a new Variant array from children.

child_type must be non-None if n_children is zero. Otherwise, the child type is determined by inspecting the first element of the children array. If child_type is non-None then it must be a definite type.

The items of the array are taken from the children array. No entry in the children array may be None.

All items in the array must have the same type, which must be the same as child_type, if given.

If the children are floating references (see Variant.ref_sink), the new instance takes ownership of them as if via Variant.ref_sink.

Parameters:

  • child_type — the element type of the new array
  • children — an array of Variant pointers, the children

new_boolean

@classmethod
def new_boolean(cls, value: bool) -> Variant

Creates a new boolean Variant instance -- either True or False.

Parameters:

  • value — a #gboolean value

new_byte

@classmethod
def new_byte(cls, value: int) -> Variant

Creates a new byte Variant instance.

Parameters:

  • value — a #guint8 value

new_bytestring

@classmethod
def new_bytestring(cls, string: list[int]) -> Variant

Creates an array-of-bytes Variant with the contents of string. This function is just like Variant.new_string except that the string need not be valid UTF-8.

The nul terminator character at the end of the string is stored in the array.

Parameters:

  • string — a normal nul-terminated string in no particular encoding

new_bytestring_array

@classmethod
def new_bytestring_array(cls, strv: list[str]) -> Variant

Constructs an array of bytestring Variant from the given array of strings.

If length is -1 then strv is None-terminated.

Parameters:

  • strv — an array of strings

new_dict_entry

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

Creates a new dictionary entry Variant. key and value must be non-None. key must be a value of a basic type (ie: not a container).

If the key or value are floating references (see Variant.ref_sink), the new instance takes ownership of them as if via Variant.ref_sink.

Parameters:

new_double

@classmethod
def new_double(cls, value: float) -> Variant

Creates a new double Variant instance.

Parameters:

  • value — a #gdouble floating point value

new_fixed_array

@classmethod
def new_fixed_array(cls, element_type: VariantType, elements: int | None, n_elements: int, element_size: int) -> Variant

Constructs a new array Variant instance, where the elements are of element_type type.

elements must be an array with fixed-sized elements. Numeric types are fixed-size as are tuples containing only other fixed-sized types.

element_size must be the size of a single element in the array. For example, if calling this function for an array of 32-bit integers, you might say sizeof(gint32). This value isn't used except for the purpose of a double-check that the form of the serialized data matches the caller's expectation.

n_elements must be the length of the elements array.

Parameters:

  • element_type — the VariantType of each element
  • elements — a pointer to the fixed array of contiguous elements
  • n_elements — the number of elements
  • element_size — the size of each element

new_from_bytes

@classmethod
def new_from_bytes(cls, type: VariantType, bytes: Bytes, trusted: bool) -> Variant

Constructs a new serialized-mode Variant instance. This is the inner interface for creation of new serialized values that gets called from various functions in gvariant.c.

A reference is taken on bytes.

The data in bytes must be aligned appropriately for the type being loaded. Otherwise this function will internally create a copy of the memory (since GLib 2.60) or (in older versions) fail and exit the process.

Parameters:

  • type — a VariantType
  • bytes — a Bytes
  • trusted — if the contents of bytes are trusted

new_from_data

@classmethod
def new_from_data(cls, type: VariantType, data: list[int], trusted: bool, notify: DestroyNotify, user_data: int | None = ...) -> Variant

Creates a new Variant instance from serialized data.

type is the type of Variant instance that will be constructed. The interpretation of data depends on knowing the type.

data is not modified by this function and must remain valid with an unchanging value until such a time as notify is called with user_data. If the contents of data change before that time then the result is undefined.

If data is trusted to be serialized data in normal form then trusted should be True. This applies to serialized data created within this process or read from a trusted location on the disk (such as a file installed in /usr/lib alongside your application). You should set trusted to False if data is read from the network, a file in the user's home directory, etc.

If data was not stored in this machine's native endianness, any multi-byte numeric values in the returned variant will also be in non-native endianness. Variant.byteswap can be used to recover the original values.

notify will be called with user_data when data is no longer needed. The exact time of this call is unspecified and might even be before this function returns.

Note: data must be backed by memory that is aligned appropriately for the type being loaded. Otherwise this function will internally create a copy of the memory (since GLib 2.60) or (in older versions) fail and exit the process.

Parameters:

  • type — a definite VariantType
  • data — the serialized data
  • trusted — True if data is definitely in normal form
  • notify — function to call when data is no longer needed
  • user_data — data for notify

new_handle

@classmethod
def new_handle(cls, value: int) -> Variant

Creates a new handle Variant instance.

By convention, handles are indexes into an array of file descriptors that are sent alongside a D-Bus message. If you're not interacting with D-Bus, you probably don't need them.

Parameters:

  • value — a #gint32 value

new_int16

@classmethod
def new_int16(cls, value: int) -> Variant

Creates a new int16 Variant instance.

Parameters:

  • value — a #gint16 value

new_int32

@classmethod
def new_int32(cls, value: int) -> Variant

Creates a new int32 Variant instance.

Parameters:

  • value — a #gint32 value

new_int64

@classmethod
def new_int64(cls, value: int) -> Variant

Creates a new int64 Variant instance.

Parameters:

  • value — a #gint64 value

new_maybe

@classmethod
def new_maybe(cls, child_type: VariantType | None = ..., child: Variant | None = ...) -> Variant

Depending on if child is None, either wraps child inside of a maybe container or creates a Nothing instance for the given type.

At least one of child_type and child must be non-None. If child_type is non-None then it must be a definite type. If they are both non-None then child_type must be the type of child.

If child is a floating reference (see Variant.ref_sink), the new instance takes ownership of child.

Parameters:

  • child_type — the VariantType of the child, or None
  • child — the child value, or None

new_object_path

@classmethod
def new_object_path(cls, object_path: str) -> Variant

Creates a D-Bus object path Variant with the contents of object_path. object_path must be a valid D-Bus object path. Use Variant.is_object_path if you're not sure.

Parameters:

  • object_path — a normal C nul-terminated string

new_objv

@classmethod
def new_objv(cls, strv: list[str]) -> Variant

Constructs an array of object paths Variant from the given array of strings.

Each string must be a valid Variant object path; see Variant.is_object_path.

If length is -1 then strv is None-terminated.

Parameters:

  • strv — an array of strings

new_signature

@classmethod
def new_signature(cls, signature: str) -> Variant

Creates a D-Bus type signature Variant with the contents of string. string must be a valid D-Bus type signature. Use Variant.is_signature if you're not sure.

Parameters:

  • signature — a normal C nul-terminated string

new_string

@classmethod
def new_string(cls, string: str) -> Variant

Creates a string Variant with the contents of string.

string must be valid UTF-8, and must not be None. To encode potentially-None strings, use g_variant_new() with ms as the format string.

Parameters:

  • string — a normal UTF-8 nul-terminated string

new_strv

@classmethod
def new_strv(cls, strv: list[str]) -> Variant

Constructs an array of strings Variant from the given array of strings.

If length is -1 then strv is None-terminated.

Parameters:

  • strv — an array of strings

new_tuple

@classmethod
def new_tuple(cls, children: list[Variant]) -> Variant

Creates a new tuple Variant out of the items in children. The type is determined from the types of children. No entry in the children array may be None.

If n_children is 0 then the unit tuple is constructed.

If the children are floating references (see Variant.ref_sink), the new instance takes ownership of them as if via Variant.ref_sink.

Parameters:

  • children — the items to make the tuple out of

new_uint16

@classmethod
def new_uint16(cls, value: int) -> Variant

Creates a new uint16 Variant instance.

Parameters:

  • value — a #guint16 value

new_uint32

@classmethod
def new_uint32(cls, value: int) -> Variant

Creates a new uint32 Variant instance.

Parameters:

  • value — a #guint32 value

new_uint64

@classmethod
def new_uint64(cls, value: int) -> Variant

Creates a new uint64 Variant instance.

Parameters:

  • value — a #guint64 value

new_variant

@classmethod
def new_variant(cls, value: Variant) -> Variant

Boxes value. The result is a Variant instance representing a variant containing the original value.

If child is a floating reference (see Variant.ref_sink), the new instance takes ownership of child.

Parameters:

Methods

byteswap

def byteswap(self) -> Variant

Performs a byteswapping operation on the contents of value. The result is that all multi-byte numeric data contained in value is byteswapped. That includes 16, 32, and 64bit signed and unsigned integers as well as file handles and double precision floating point values.

This function is an identity mapping on any value that does not contain multi-byte numeric data. That include strings, booleans, bytes and containers containing only these things (recursively).

While this function can safely handle untrusted, non-normal data, it is recommended to check whether the input is in normal form beforehand, using Variant.is_normal_form, and to reject non-normal inputs if your application can be strict about what inputs it rejects.

The returned value is always in normal form and is marked as trusted. A full, not floating, reference is returned.

check_format_string

def check_format_string(self, format_string: str, copy_only: bool) -> bool

Checks if calling g_variant_get() with format_string on value would be valid from a type-compatibility standpoint. format_string is assumed to be a valid format string (from a syntactic standpoint).

If copy_only is True then this function additionally checks that it would be safe to call Variant.unref on value immediately after the call to g_variant_get() without invalidating the result. This is only possible if deep copies are made (ie: there are no pointers to the data inside of the soon-to-be-freed Variant instance). If this check fails then a g_critical() is printed and False is returned.

This function is meant to be used by functions that wish to provide varargs accessors to Variant values of uncertain values (eg: g_variant_lookup() or g_menu_model_get_item_attribute()).

Parameters:

  • format_string — a valid Variant format string
  • copy_only — True to ensure the format string makes deep copies

classify

def classify(self) -> VariantClass

Classifies value according to its top-level type.

compare

def compare(self, two: Variant) -> int

Compares one and two.

The types of one and two are #gconstpointer only to allow use of this function with Tree, PtrArray, etc. They must each be a Variant.

Comparison is only defined for basic types (ie: booleans, numbers, strings). For booleans, False is less than True. Numbers are ordered in the usual way. Strings are in ASCII lexographical order.

It is a programmer error to attempt to compare container values or two values that have types that are not exactly equal. For example, you cannot compare a 32-bit signed integer with a 32-bit unsigned integer. Also note that this function is not particularly well-behaved when it comes to comparison of doubles; in particular, the handling of incomparable values (ie: NaN) is undefined.

If you only require an equality comparison, Variant.equal is more general.

Parameters:

  • two — a Variant instance of the same type

dup_bytestring

def dup_bytestring(self) -> list[int]

Similar to Variant.get_bytestring except that instead of returning a constant string, the string is duplicated.

The return value must be freed using free.

dup_bytestring_array

def dup_bytestring_array(self) -> list[str]

Gets the contents of an array of array of bytes Variant. This call makes a deep copy; the return result should be released with strfreev.

If length is non-None then the number of elements in the result is stored there. In any case, the resulting array will be None-terminated.

For an empty array, length will be set to 0 and a pointer to a None pointer will be returned.

dup_objv

def dup_objv(self) -> list[str]

Gets the contents of an array of object paths Variant. This call makes a deep copy; the return result should be released with strfreev.

If length is non-None then the number of elements in the result is stored there. In any case, the resulting array will be None-terminated.

For an empty array, length will be set to 0 and a pointer to a None pointer will be returned.

dup_string

def dup_string(self) -> tuple[str, int]

Similar to Variant.get_string except that instead of returning a constant string, the string is duplicated.

The string will always be UTF-8 encoded.

The return value must be freed using free.

dup_strv

def dup_strv(self) -> list[str]

Gets the contents of an array of strings Variant. This call makes a deep copy; the return result should be released with strfreev.

If length is non-None then the number of elements in the result is stored there. In any case, the resulting array will be None-terminated.

For an empty array, length will be set to 0 and a pointer to a None pointer will be returned.

equal

def equal(self, two: Variant) -> bool

Checks if one and two have the same type and value.

The types of one and two are #gconstpointer only to allow use of this function with HashTable. They must each be a Variant.

Parameters:

get_boolean

def get_boolean(self) -> bool

Returns the boolean value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_BOOLEAN.

get_byte

def get_byte(self) -> int

Returns the byte value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_BYTE.

get_bytestring

def get_bytestring(self) -> list[int]

Returns the string value of a Variant instance with an array-of-bytes type. The string has no particular encoding.

If the array does not end with a nul terminator character, the empty string is returned. For this reason, you can always trust that a non-None nul-terminated string will be returned by this function.

If the array contains a nul terminator character somewhere other than the last byte then the returned string is the string, up to the first such nul character.

g_variant_get_fixed_array() should be used instead if the array contains arbitrary data that could not be nul-terminated or could contain nul bytes.

It is an error to call this function with a value that is not an array of bytes.

The return value remains valid as long as value exists.

get_bytestring_array

def get_bytestring_array(self) -> list[str]

Gets the contents of an array of array of bytes Variant. This call makes a shallow copy; the return result should be released with free, but the individual strings must not be modified.

If length is non-None then the number of elements in the result is stored there. In any case, the resulting array will be None-terminated.

For an empty array, length will be set to 0 and a pointer to a None pointer will be returned.

get_child_value

def get_child_value(self, index_: int) -> Variant

Reads a child item out of a container Variant instance. This includes variants, maybes, arrays, tuples and dictionary entries. It is an error to call this function on any other type of Variant.

It is an error if index_ is greater than the number of child items in the container. See Variant.n_children.

The returned value is never floating. You should free it with Variant.unref when you're done with it.

Note that values borrowed from the returned child are not guaranteed to still be valid after the child is freed even if you still hold a reference to value, if value has not been serialized at the time this function is called. To avoid this, you can serialize value by calling Variant.get_data and optionally ignoring the return value.

There may be implementation specific restrictions on deeply nested values, which would result in the unit tuple being returned as the child value, instead of further nested children. Variant is guaranteed to handle nesting up to at least 64 levels.

This function is O(1).

Parameters:

  • index_ — the index of the child to fetch

get_data

def get_data(self) -> int | None

Returns a pointer to the serialized form of a Variant instance. The returned data may not be in fully-normalised form if read from an untrusted source. The returned data must not be freed; it remains valid for as long as value exists.

If value is a fixed-sized value that was deserialized from a corrupted serialized container then None may be returned. In this case, the proper thing to do is typically to use the appropriate number of nul bytes in place of value. If value is not fixed-sized then None is never returned.

In the case that value is already in serialized form, this function is O(1). If the value is not already in serialized form, serialization occurs implicitly and is approximately O(n) in the size of the result.

To deserialize the data returned by this function, in addition to the serialized data, you must know the type of the Variant, and (if the machine might be different) the endianness of the machine that stored it. As a result, file formats or network messages that incorporate serialized GVariants must include this information either implicitly (for instance "the file always contains a G_VARIANT_TYPE_VARIANT and it is always in little-endian order") or explicitly (by storing the type and/or endianness in addition to the serialized data).

get_data_as_bytes

def get_data_as_bytes(self) -> Bytes

Returns a pointer to the serialized form of a Variant instance. The semantics of this function are exactly the same as Variant.get_data, except that the returned Bytes holds a reference to the variant data.

get_double

def get_double(self) -> float

Returns the double precision floating point value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_DOUBLE.

get_handle

def get_handle(self) -> int

Returns the 32-bit signed integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_HANDLE.

By convention, handles are indexes into an array of file descriptors that are sent alongside a D-Bus message. If you're not interacting with D-Bus, you probably don't need them.

get_int16

def get_int16(self) -> int

Returns the 16-bit signed integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_INT16.

get_int32

def get_int32(self) -> int

Returns the 32-bit signed integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_INT32.

get_int64

def get_int64(self) -> int

Returns the 64-bit signed integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_INT64.

get_maybe

def get_maybe(self) -> Variant | None

Given a maybe-typed Variant instance, extract its value. If the value is Nothing, then this function returns None.

get_normal_form

def get_normal_form(self) -> Variant

Gets a Variant instance that has the same value as value and is trusted to be in normal form.

If value is already trusted to be in normal form then a new reference to value is returned.

If value is not already trusted, then it is scanned to check if it is in normal form. If it is found to be in normal form then it is marked as trusted and a new reference to it is returned.

If value is found not to be in normal form then a new trusted Variant is created with the same value as value. The non-normal parts of value will be replaced with default values which are guaranteed to be in normal form.

It makes sense to call this function if you've received Variant data from untrusted sources and you want to ensure your serialized output is definitely in normal form.

If value is already in normal form, a new reference will be returned (which will be floating if value is floating). If it is not in normal form, the newly created Variant will be returned with a single non-floating reference. Typically, Variant.take_ref should be called on the return value from this function to guarantee ownership of a single non-floating reference to it.

get_objv

def get_objv(self) -> list[str]

Gets the contents of an array of object paths Variant. This call makes a shallow copy; the return result should be released with free, but the individual strings must not be modified.

If length is non-None then the number of elements in the result is stored there. In any case, the resulting array will be None-terminated.

For an empty array, length will be set to 0 and a pointer to a None pointer will be returned.

get_size

def get_size(self) -> int

Determines the number of bytes that would be required to store value with Variant.store.

If value has a fixed-sized type then this function always returned that fixed size.

In the case that value is already in serialized form or the size has already been calculated (ie: this function has been called before) then this function is O(1). Otherwise, the size is calculated, an operation which is approximately O(n) in the number of values involved.

get_string

def get_string(self) -> tuple[str, int]

Returns the string value of a Variant instance with a string type. This includes the types G_VARIANT_TYPE_STRING, G_VARIANT_TYPE_OBJECT_PATH and G_VARIANT_TYPE_SIGNATURE.

The string will always be UTF-8 encoded, will never be None, and will never contain nul bytes.

If length is non-None then the length of the string (in bytes) is returned there. For trusted values, this information is already known. Untrusted values will be validated and, if valid, a strlen() will be performed. If invalid, a default value will be returned — for G_VARIANT_TYPE_OBJECT_PATH, this is "/", and for other types it is the empty string.

It is an error to call this function with a value of any type other than those three.

The return value remains valid as long as value exists.

get_strv

def get_strv(self) -> list[str]

Gets the contents of an array of strings Variant. This call makes a shallow copy; the return result should be released with free, but the individual strings must not be modified.

If length is non-None then the number of elements in the result is stored there. In any case, the resulting array will be None-terminated.

For an empty array, length will be set to 0 and a pointer to a None pointer will be returned.

get_type

def get_type(self) -> VariantType

Determines the type of value.

The return value is valid for the lifetime of value and must not be freed.

get_type_string

def get_type_string(self) -> str

Returns the type string of value. Unlike the result of calling g_variant_type_peek_string(), this string is nul-terminated. This string belongs to Variant and must not be freed.

get_uint16

def get_uint16(self) -> int

Returns the 16-bit unsigned integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_UINT16.

get_uint32

def get_uint32(self) -> int

Returns the 32-bit unsigned integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_UINT32.

get_uint64

def get_uint64(self) -> int

Returns the 64-bit unsigned integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_UINT64.

get_variant

def get_variant(self) -> Variant

Unboxes value. The result is the Variant instance that was contained in value.

hash

def hash(self) -> int

Generates a hash value for a Variant instance.

The output of this function is guaranteed to be the same for a given value only per-process. It may change between different processor architectures or even different versions of GLib. Do not use this function as a basis for building protocols or file formats.

The type of value is #gconstpointer only to allow use of this function with HashTable. value must be a Variant.

is_container

def is_container(self) -> bool

Checks if value is a container.

is_floating

def is_floating(self) -> bool

Checks whether value has a floating reference count.

This function should only ever be used to assert that a given variant is or is not floating, or for debug purposes. To acquire a reference to a variant that might be floating, always use Variant.ref_sink or Variant.take_ref.

See Variant.ref_sink for more information about floating reference counts.

is_normal_form

def is_normal_form(self) -> bool

Checks if value is in normal form.

The main reason to do this is to detect if a given chunk of serialized data is in normal form: load the data into a Variant using Variant.new_from_data and then use this function to check.

If value is found to be in normal form then it will be marked as being trusted. If the value was already marked as being trusted then this function will immediately return True.

There may be implementation specific restrictions on deeply nested values. GVariant is guaranteed to handle nesting up to at least 64 levels.

is_of_type

def is_of_type(self, type: VariantType) -> bool

Checks if a value has a type matching the provided type.

Parameters:

lookup_value

def lookup_value(self, key: str, expected_type: VariantType | None = ...) -> Variant

Looks up a value in a dictionary Variant.

This function works with dictionaries of the type a{s*} (and equally well with type a{o*}), but we only further discuss the string case for sake of clarity).

In the event that dictionary has the type a{sv}, the expected_type string specifies what type of value is expected to be inside of the variant. If the value inside the variant has a different type then None is returned. In the event that dictionary has a value type other than v then expected_type must directly match the value type and it is used to unpack the value directly or an error occurs.

In either case, if key is not found in dictionary, None is returned.

If the key is found and the value has the correct type, it is returned. If expected_type was specified then any non-None return value will have this type.

This function is currently implemented with a linear scan. If you plan to do many lookups then VariantDict may be more efficient.

Parameters:

  • key — the key to look up in the dictionary
  • expected_type — a VariantType, or None

n_children

def n_children(self) -> int

Determines the number of children in a container Variant instance. This includes variants, maybes, arrays, tuples and dictionary entries. It is an error to call this function on any other type of Variant.

For variants, the return value is always 1. For values with maybe types, it is always zero or one. For arrays, it is the length of the array. For tuples it is the number of tuple items (which depends only on the type). For dictionary entries, it is always 2

This function is O(1).

print

def print(self, type_annotate: bool) -> str

Pretty-prints value in the format understood by Variant.parse.

The format is described here.

If type_annotate is True, then type information is included in the output.

Parameters:

  • type_annotate — True if type information should be included in the output

ref

def ref(self) -> Variant

Increases the reference count of value.

ref_sink

def ref_sink(self) -> Variant

Variant uses a floating reference count system. All functions with names starting with g_variant_new_ return floating references.

Calling Variant.ref_sink on a Variant with a floating reference will convert the floating reference into a full reference. Calling Variant.ref_sink on a non-floating Variant results in an additional normal reference being added.

In other words, if the value is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference. If the value is not floating, then this call adds a new normal reference increasing the reference count by one.

All calls that result in a Variant instance being inserted into a container will call Variant.ref_sink on the instance. This means that if the value was just created (and has only its floating reference) then the container will assume sole ownership of the value at that point and the caller will not need to unreference it. This makes certain common styles of programming much easier while still maintaining normal refcounting semantics in situations where values are not floating.

store

def store(self, data: int) -> None

Stores the serialized form of value at data. data should be large enough. See Variant.get_size.

The stored data is in machine native byte order but may not be in fully-normalised form if read from an untrusted source. See Variant.get_normal_form for a solution.

As with Variant.get_data, to be able to deserialize the serialized variant successfully, its type and (if the destination machine might be different) its endianness must also be available.

This function is approximately O(n) in the size of data.

Parameters:

  • data — the location to store the serialized data at

take_ref

def take_ref(self) -> Variant

If value is floating, sink it. Otherwise, do nothing.

Typically you want to use Variant.ref_sink in order to automatically do the correct thing with respect to floating or non-floating references, but there is one specific scenario where this function is helpful.

The situation where this function is helpful is when creating an API that allows the user to provide a callback function that returns a Variant. We certainly want to allow the user the flexibility to return a non-floating reference from this callback (for the case where the value that is being returned already exists).

At the same time, the style of the Variant API makes it likely that for newly-created Variant instances, the user can be saved some typing if they are allowed to return a Variant with a floating reference.

Using this function on the return value of the user's callback allows the user to do whichever is more convenient for them. The caller will always receives exactly one full reference to the value: either the one that was returned in the first place, or a floating reference that has been converted to a full reference.

This function has an odd interaction when combined with Variant.ref_sink running at the same time in another thread on the same Variant instance. If Variant.ref_sink runs first then the result will be that the floating reference is converted to a hard reference. If Variant.take_ref runs first then the result will be that the floating reference is converted to a hard reference and an additional reference on top of that one is added. It is best to avoid this situation.

unref

def unref(self) -> None

Decreases the reference count of value. When its reference count drops to 0, the memory used by the variant is freed.

Static functions

is_object_path

@staticmethod
def is_object_path(string: str) -> bool

Determines if a given string is a valid D-Bus object path. You should ensure that a string is a valid D-Bus object path before passing it to Variant.new_object_path.

A valid object path starts with / followed by zero or more sequences of characters separated by / characters. Each sequence must contain only the characters [A-Z][a-z][0-9]_. No sequence (including the one following the final / character) may be empty.

Parameters:

  • string — a normal C nul-terminated string

is_signature

@staticmethod
def is_signature(string: str) -> bool

Determines if a given string is a valid D-Bus type signature. You should ensure that a string is a valid D-Bus type signature before passing it to Variant.new_signature.

D-Bus type signatures consist of zero or more definite VariantType strings in sequence.

Parameters:

  • string — a normal C nul-terminated string

parse

@staticmethod
def parse(type: VariantType | None, text: str, limit: str | None = ..., endptr: str | None = ...) -> Variant

Parses a Variant from a text representation.

A single Variant is parsed from the content of text.

The format is described here.

The memory at limit will never be accessed and the parser behaves as if the character at limit is the nul terminator. This has the effect of bounding text.

If endptr is non-None then text is permitted to contain data following the value that this function parses and endptr will be updated to point to the first character past the end of the text parsed by this function. If endptr is None and there is extra data then an error is returned.

If type is non-None then the value will be parsed to have that type. This may result in additional parse errors (in the case that the parsed value doesn't fit the type) but may also result in fewer errors (in the case that the type would have been ambiguous, such as with empty arrays).

In the event that the parsing is successful, the resulting Variant is returned. It is never floating, and must be freed with Variant.unref.

In case of any error, None will be returned. If error is non-None then it will be set to reflect the error that occurred.

Officially, the language understood by the parser is “any string produced by Variant.print”. This explicitly includes g_variant_print()’s annotated types like int64 -1000.

There may be implementation specific restrictions on deeply nested values, which would result in a VariantParseError.RECURSION error. Variant is guaranteed to handle nesting up to at least 64 levels.

Parameters:

  • type — a VariantType, or None
  • text — a string containing a GVariant in text form
  • limit — a pointer to the end of text, or None
  • endptr — a location to store the end pointer, or None

parse_error_print_context

@staticmethod
def parse_error_print_context(error: Error, source_str: str) -> str

Pretty-prints a message showing the context of a Variant parse error within the string for which parsing was attempted.

The resulting string is suitable for output to the console or other monospace media where newlines are treated in the usual way.

The message will typically look something like one of the following:

unterminated string constant:
  (1, 2, 3, 'abc
            ^^^^

or

unable to find a common type:
  [1, 2, 3, 'str']
   ^        ^^^^^

The format of the message may change in a future version.

error must have come from a failed attempt to Variant.parse and source_str must be exactly the same string that caused the error. If source_str was not nul-terminated when you passed it to Variant.parse then you must add nul termination before using this function.

Parameters:

parse_error_quark

@staticmethod
def parse_error_quark() -> Quark

parser_get_error_quark

@staticmethod
def parser_get_error_quark() -> Quark

:::warning Deprecated This API is deprecated. :::

Same as g_variant_error_quark().