class QJsonValue#

The QJsonValue class encapsulates a value in JSON. More…

Synopsis#

Methods#

Static functions#

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description#

A value in JSON can be one of 6 basic types:

JSON is a format to store structured data. It has 6 basic data types:

A value can represent any of the above data types. In addition, QJsonValue has one special flag to represent undefined values. This can be queried with isUndefined() .

The type of the value can be queried with type() or accessors like isBool() , isString() , and so on. Likewise, the value can be converted to the type stored in it using the toBool() , toString() and so on.

Values are strictly typed internally and contrary to QVariant will not attempt to do any implicit type conversions. This implies that converting to a type that is not stored in the value will return a default constructed return value.

QJsonValueRef#

QJsonValueRef is a helper class for QJsonArray and QJsonObject . When you get an object of type QJsonValueRef , you can use it as if it were a reference to a QJsonValue . If you assign to it, the assignment will apply to the element in the QJsonArray or QJsonObject from which you got the reference.

The following methods return QJsonValueRef :

  • QJsonArray ::operator[](qsizetype i)

  • QJsonObject ::operator[](const QString & key) const

See also

JSON Support in Qt Saving and Loading a Game

class Type#

This enum describes the type of the JSON value.

Constant

Description

QJsonValue.Null

A Null value

QJsonValue.Bool

A boolean value. Use toBool() to convert to a bool.

QJsonValue.Double

A number value. Use toDouble() to convert to a double, or toInteger() to convert to a qint64.

QJsonValue.String

A string. Use toString() to convert to a QString .

QJsonValue.Array

An array. Use toArray() to convert to a QJsonArray .

QJsonValue.Object

An object. Use toObject() to convert to a QJsonObject .

QJsonValue.Undefined

The value is undefined. This is usually returned as an error condition, when trying to read an out of bounds value in an array or a non existent key in an object.
__init__(v)#
Parameters:

v – int

This is an overloaded function.

Creates a value of type Double, with value v. NOTE: the integer limits for IEEE 754 double precision data is 2^53 (-9007199254740992 to +9007199254740992). If you pass in values outside this range expect a loss of precision to occur.

__init__([arg__1=QJsonValue.Type.Null])
Parameters:

arg__1 – Type

Creates a QJsonValue of type type.

The default is to create a Null value.

__init__(n)
Parameters:

n – int

This is an overloaded function.

Creates a value of type Double, with value v.

__init__(n)
Parameters:

n – float

Creates a value of type Double, with value v.

__init__(s)
Parameters:

s – str

Creates a value of type String with value s, assuming UTF-8 encoding of the input.

You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications.

__init__(s)
Parameters:

s – str

Creates a value of type String, with value s.

__init__(other)
Parameters:

other – QJsonValue

Creates a copy of other.

__init__(o)
Parameters:

o – QJsonObject

Creates a value of type Object, with value o.

__init__(a)
Parameters:

a – QJsonArray

Creates a value of type Array, with value a.

__init__(b)
Parameters:

b – bool

Creates a value of type Bool, with value b.

__init__(s)
Parameters:

s – QLatin1String

static fromVariant(variant)#
Parameters:

variant – object

Return type:

QJsonValue

Converts variant to a QJsonValue and returns it.

The conversion will convert QVariant types as follows:

Source type

Destination type

Null

Bool

Double

String

Array

Object

String . The conversion will use toString() with flag FullyEncoded , so as to ensure maximum compatibility in parsing the URL

String . Since Qt 5.11, the resulting string will not include braces

Whichever type toJsonValue() returns.

Array . See toJsonValue() for conversion restrictions.

QJsonValue::Map. See toJsonValue() for conversion restrictions and the “stringification” of map keys.

Loss of information and other types#

QVariant can carry more information than is representable in JSON. If the QVariant is not one of the types above, the conversion is not guaranteed and is subject to change in future versions of Qt, as the UUID one did. Code should strive not to use any other types than those listed above.

If isNull() returns true, a null QJsonValue is returned or inserted into the list or object, regardless of the type carried by QVariant . Note the behavior change in Qt 6.0 affecting isNull() also affects this function.

A floating point value that is either an infinity or NaN will be converted to a null JSON value. Since Qt 6.0, QJsonValue can store the full precision of any 64-bit signed integer without loss, but in previous versions values outside the range of ±2^53 may lose precision. Unsigned 64-bit values greater than or equal to 2^63 will either lose precision or alias to negative values, so ULongLong should be avoided.

For other types not listed above, a conversion to string will be attempted, usually but not always by calling toString() . If the conversion fails the value is replaced by a null JSON value. Note that toString() is also lossy for the majority of types. For example, if the passed QVariant is representing raw byte array data, it is recommended to pre-encode it to Base64 (or another lossless encoding), otherwise a lossy conversion using fromUtf8() will be used.

Please note that the conversions via toString() are subject to change at any time. Both QVariant and QJsonValue may be extended in the future to support more types, which will result in a change in how this function performs conversions.

isArray()#
Return type:

bool

Returns true if the value contains an array.

See also

toArray()

isBool()#
Return type:

bool

Returns true if the value contains a boolean.

See also

toBool()

isDouble()#
Return type:

bool

Returns true if the value contains a double.

See also

toDouble()

isNull()#
Return type:

bool

Returns true if the value is null.

isObject()#
Return type:

bool

Returns true if the value contains an object.

See also

toObject()

isString()#
Return type:

bool

Returns true if the value contains a string.

See also

toString()

isUndefined()#
Return type:

bool

Returns true if the value is undefined. This can happen in certain error cases as e.g. accessing a non existing key in a QJsonObject .

__ne__(other)#
Parameters:

other – QJsonValue

Return type:

bool

Returns true if the value is not equal to other.

__eq__(other)#
Parameters:

other – QJsonValue

Return type:

bool

Returns true if the value is equal to other.

operator(key)#
Parameters:

key – QLatin1String

Return type:

QJsonValue

operator(key)
Parameters:

key – str

Return type:

QJsonValue

This is an overloaded function.

operator(key)
Parameters:

key – str

Return type:

QJsonValue

Returns a QJsonValue representing the value for the key key.

Equivalent to calling toObject() .value(key).

The returned QJsonValue is Undefined if the key does not exist, or if isObject() is false.

See also

QJsonValue isUndefined() QJsonObject

operator(i)
Parameters:

i – int

Return type:

QJsonValue

Returns a QJsonValue representing the value for index i.

Equivalent to calling toArray() .at(i).

The returned QJsonValue is Undefined , if i is out of bounds, or if isArray() is false.

swap(other)#
Parameters:

other – QJsonValue

Swaps the value other with this. This operation is very fast and never fails.

toArray()#
Return type:

QJsonArray

This is an overloaded function.

Converts the value to an array and returns it.

If type() is not Array, a QJsonArray() will be returned.

toArray(defaultValue)
Parameters:

defaultValue – QJsonArray

Return type:

QJsonArray

Converts the value to an array and returns it.

If type() is not Array, the defaultValue will be returned.

toBool([defaultValue=false])#
Parameters:

defaultValue – bool

Return type:

bool

Converts the value to a bool and returns it.

If type() is not bool, the defaultValue will be returned.

toDouble([defaultValue=0])#
Parameters:

defaultValue – float

Return type:

float

Converts the value to a double and returns it.

If type() is not Double, the defaultValue will be returned.

toInt([defaultValue=0])#
Parameters:

defaultValue – int

Return type:

int

Converts the value to an int and returns it.

If type() is not Double or the value is not a whole number, the defaultValue will be returned.

toInteger([defaultValue=0])#
Parameters:

defaultValue – int

Return type:

int

Converts the value to an integer and returns it.

If type() is not Double or the value is not a whole number representable as qint64, the defaultValue will be returned.

toObject()#
Return type:

QJsonObject

This is an overloaded function.

Converts the value to an object and returns it.

If type() is not Object, the QJsonObject() will be returned.

toObject(defaultValue)
Parameters:

defaultValue – QJsonObject

Return type:

QJsonObject

Converts the value to an object and returns it.

If type() is not Object, the defaultValue will be returned.

toString()#
Return type:

str

Converts the value to a QString and returns it.

If type() is not String, a null QString will be returned.

See also

isNull()

toString(defaultValue)
Parameters:

defaultValue – str

Return type:

str

Converts the value to a QString and returns it.

If type() is not String, the defaultValue will be returned.

toVariant()#
Return type:

object

Converts the value to a QVariant() .

The QJsonValue types will be converted as follows:

See also

fromVariant()

type()#
Return type:

Type

Returns the type of the value.

See also

Type