Class: QgsClassificationMethod¶

An abstract class for implementations of classification methods.

Class Hierarchy¶

Subclasses¶

`QgsClassificationCustom`	A dummy implementation class method which does not compute any breaks.
`QgsClassificationEqualInterval`	A classification method which uses equal width intervals.
`QgsClassificationFixedInterval`	Implementation of a fixed interval classification.
`QgsClassificationJenks`	A classification method for natural breaks, based on Jenks method.
`QgsClassificationLogarithmic`	Implementation of a logarithmic scale method for classification.
`QgsClassificationPrettyBreaks`	A classification method which applies pretty breaks to data.
`QgsClassificationQuantile`	A classification method which creates classes based on quantiles.
`QgsClassificationStandardDeviation`	A classification method which classifies based on standard deviation of values.

Abstract Methods

`clone`	Returns a clone of the method.
`id`	The id of the method as saved in the project, must be unique in registry
`name`	The readable and translate name of the method

Methods

`classes`	This will calculate the classes for a given layer to define the classes.
`classesV2`	This will calculate the classes for a given layer to define the classes.
`codeComplexity`	Code complexity as the exponent in Big O notation
`flags`	Returns the classification flags.
`labelForRange`	Returns the label for a range
`labelFormat`	Returns the format of the label for the classes
`labelPrecision`	Returns the precision for the formatting of the labels
`labelTrimTrailingZeroes`	Returns if the trailing 0 are trimmed in the label
`parameterDefinition`	Returns the parameter from its name
`parameterDefinitions`	Returns the list of parameters
`parameterValues`	Returns the values of the processing parameters.
`save`	Saves the method to a DOM element and return it
`setLabelFormat`	Defines the format of the labels for the classes, using %1 and %2 for the bounds
`setLabelPrecision`	Defines the precision for the formatting of the labels
`setLabelTrimTrailingZeroes`	Defines if the trailing 0 are trimmed in the label
`setParameterValues`	Defines the values of the additional parameters
`setSymmetricMode`	Defines if the symmetric mode is enables and configures its parameters.
`symmetricModeAvailable`	Returns if the method supports symmetric calculation
`symmetricModeEnabled`	Returns if the symmetric mode is enabled
`symmetryAstride`	Returns if the symmetric mode is astride if `True`, it will remove the symmetry point break so that the 2 classes form only one
`symmetryPoint`	Returns the symmetry point for symmetric mode

Virtual Methods

In PyQGIS, only methods marked as virtual can be safely overridden in a Python subclass of QgsClassificationMethod. See the FAQ for more details.

`icon`	The icon of the method
`readXml`	Reads extra information to apply it to the method
`valuesRequired`	Returns if the method requires values to calculate the classes If not, bounds are sufficient
`writeXml`	Writes extra information about the method

Static Methods

`create`	Reads the DOM element and return a new classification method from it
`makeBreaksSymmetric`	Remove the breaks that are above the existing opposite sign classes to keep colors symmetrically balanced around symmetryPoint Does not put a break on the symmetryPoint.
`rangesToBreaks`	Transforms a list of classes to a list of breaks

Attributes

`IgnoresClassCount`
`Inner`
`LowerBound`
`MAX_PRECISION`
`MIN_PRECISION`
`NoFlag`
`SymmetricModeAvailable`
`UpperBound`
`ValuesNotRequired`

class qgis.core.QgsClassificationMethod[source]¶

Bases: object

__init__(properties: QgsClassificationMethod.MethodProperties | QgsClassificationMethod.MethodProperty = QgsClassificationMethod.NoFlag, codeComplexity: int = 1)

Creates a classification method.

Parameters:

properties (Union[QgsClassificationMethod.MethodProperties, QgsClassificationMethod.MethodProperty] = QgsClassificationMethod.NoFlag) – The properties of the implemented method
codeComplexity (int = 1) – as the exponent in the big O notation

__init__(a0: QgsClassificationMethod)

Parameters:: a0 (QgsClassificationMethod)

class ClassPosition¶: Bases: int

IgnoresClassCount = 8¶

Inner = 1¶

LowerBound = 0¶

MAX_PRECISION = 15¶

MIN_PRECISION = -6¶

class MethodProperties¶
class MethodProperties(f: QgsClassificationMethod.MethodProperties | QgsClassificationMethod.MethodProperty)
class MethodProperties(a0: QgsClassificationMethod.MethodProperties): Bases: object

class MethodProperty¶: Bases: int

NoFlag = 0¶

SymmetricModeAvailable = 4¶

UpperBound = 2¶

ValuesNotRequired = 2¶

classes(self, layer: QgsVectorLayer | None, expression: str | None, nclasses: int) → List[QgsClassificationRange]¶

This will calculate the classes for a given layer to define the classes.

Parameters:

layer (Optional[QgsVectorLayer]) – The vector layer
expression (Optional[str]) – The name of the field on which the classes are calculated
nclasses (int) – The number of classes to be returned

Deprecated since version 3.38: Use classesV2() instead.

Return type:: List[QgsClassificationRange]

classes(self, values: Iterable[float], nclasses: int) → List[QgsClassificationRange]

This will calculate the classes for a list of values.

Parameters:

values (Iterable[float]) – The list of values
nclasses (int) – The number of classes to be returned

Return type:

List[QgsClassificationRange]

classes(self, minimum: float, maximum: float, nclasses: int) → List[QgsClassificationRange]

This will calculate the classes for defined bounds without any values.

Warning

If the method implementation requires values, this will return an empty list.

Parameters:

minimum (float) – The minimum value for the breaks
maximum (float) – The maximum value for the breaks
nclasses (int) – The number of classes to be returned

Return type:

List[QgsClassificationRange]

classesV2(self, layer: QgsVectorLayer | None, expression: str | None, nclasses: int)¶

This will calculate the classes for a given layer to define the classes.

Parameters:

layer (Optional[QgsVectorLayer]) – The vector layer
expression (Optional[str]) – The name of the field on which the classes are calculated
nclasses (int) -> (List[QgsClassificationRange]) – The number of classes to be returned

Returns:

list of generated classes
error: error string if an error occurred while generating the classes

Added in version 3.38.

abstract clone(self) → QgsClassificationMethod | None¶

Returns a clone of the method. Implementation can take advantage of copyBase method which copies the parameters of the base class

Return type:: Optional[QgsClassificationMethod]

codeComplexity(self) → int[source]¶

Code complexity as the exponent in Big O notation

Return type:: int

static create(element: QDomElement, context: QgsReadWriteContext) → QgsClassificationMethod | None¶

Reads the DOM element and return a new classification method from it

Parameters:

element (QDomElement) – the DOM element
context (QgsReadWriteContext) – the read/write context

Return type:

Optional[QgsClassificationMethod]

flags(self) → QgsClassificationMethod.MethodProperties[source]¶

Returns the classification flags.

Added in version 3.26.

Return type:: QgsClassificationMethod.MethodProperties

virtual icon(self) → QIcon[source]¶

The icon of the method

Return type:: QIcon

abstract id(self) → str[source]¶

The id of the method as saved in the project, must be unique in registry

Return type:: str

labelForRange(self, lowerValue: float, upperValue: float, position: QgsClassificationMethod.ClassPosition = QgsClassificationMethod.Inner) → str[source]¶

Returns the label for a range

Parameters:

lowerValue (float)
upperValue (float)
position (QgsClassificationMethod.ClassPosition = QgsClassificationMethod.Inner)

Return type:

str

labelForRange(self, range: QgsRendererRange, position: QgsClassificationMethod.ClassPosition = QgsClassificationMethod.Inner) → str[source]

Returns the label for a range

Parameters:

range (QgsRendererRange)
position (QgsClassificationMethod.ClassPosition = QgsClassificationMethod.Inner)

Return type:

str

labelFormat(self) → str[source]¶

Returns the format of the label for the classes

Return type:: str

labelPrecision(self) → int[source]¶

Returns the precision for the formatting of the labels

Return type:: int

labelTrimTrailingZeroes(self) → bool[source]¶

Returns if the trailing 0 are trimmed in the label

Return type:: bool

static makeBreaksSymmetric(breaks: Iterable[float], symmetryPoint: float, astride: bool) → List[float][source]¶

Remove the breaks that are above the existing opposite sign classes to keep colors symmetrically balanced around symmetryPoint Does not put a break on the symmetryPoint. This is done before.

Parameters:

breaks (Iterable[float]) – The breaks of an already-done classification
symmetryPoint (float) – The point around which we want a symmetry
astride (bool) – A bool indicating if the symmetry is made astride the symmetryPoint or not ( [-1,1] vs. [-1,0][0,1] )

Return type:

List[float]

abstract name(self) → str[source]¶

The readable and translate name of the method

Return type:: str

parameterDefinition(self, parameterName: str | None) → QgsProcessingParameterDefinition | None[source]¶

Returns the parameter from its name

Added in version 3.12.

Parameters:: parameterName (Optional[str])
Return type:: Optional[QgsProcessingParameterDefinition]

parameterDefinitions(self) → List[QgsProcessingParameterDefinition][source]¶

Returns the list of parameters

Added in version 3.12.

Return type:: List[QgsProcessingParameterDefinition]

parameterValues(self) → Dict[str, Any][source]¶

Returns the values of the processing parameters. One could use QgsProcessingParameters.parameterAsXxxx to retrieve the actual value of a parameter.

Added in version 3.12.

Return type:: Dict[str, Any]

static rangesToBreaks(classes: Iterable[QgsClassificationRange]) → List[float]¶

Transforms a list of classes to a list of breaks

Parameters:: classes (Iterable[QgsClassificationRange])
Return type:: List[float]

virtual readXml(self, element: QDomElement, context: QgsReadWriteContext)[source]¶

Reads extra information to apply it to the method

Parameters:

element (QDomElement)
context (QgsReadWriteContext)

save(self, doc: QDomDocument, context: QgsReadWriteContext) → QDomElement[source]¶

Saves the method to a DOM element and return it

Parameters:

doc (QDomDocument) – the DOM document
context (QgsReadWriteContext) – the read/write context

Return type:

QDomElement

setLabelFormat(self, format: str | None)[source]¶

Defines the format of the labels for the classes, using %1 and %2 for the bounds

Parameters:: format (Optional[str])

setLabelPrecision(self, labelPrecision: int)[source]¶

Defines the precision for the formatting of the labels

Parameters:: labelPrecision (int)

setLabelTrimTrailingZeroes(self, trimTrailingZeroes: bool)[source]¶

Defines if the trailing 0 are trimmed in the label

Parameters:: trimTrailingZeroes (bool)

setParameterValues(self, values: Dict[str, Any])[source]¶

Defines the values of the additional parameters

Added in version 3.12.

Parameters:: values (Dict[str, Any])

setSymmetricMode(self, enabled: bool, symmetryPoint: float = 0, symmetryAstride: bool = False)[source]¶

Defines if the symmetric mode is enables and configures its parameters. If the symmetric mode is not available in the current implementation, calling this method has no effect.

Parameters:

enabled (bool) – if the symmetric mode is enabled
symmetryPoint (float = 0) – the value of the symmetry point
symmetryAstride (bool = False) – if True, it will remove the symmetry point break so that the 2 classes form only one

symmetricModeAvailable(self) → bool[source]¶

Returns if the method supports symmetric calculation

Return type:: bool

symmetricModeEnabled(self) → bool[source]¶

Returns if the symmetric mode is enabled

Return type:: bool

symmetryAstride(self) → bool[source]¶

Returns if the symmetric mode is astride if True, it will remove the symmetry point break so that the 2 classes form only one

Return type:: bool

symmetryPoint(self) → float[source]¶

Returns the symmetry point for symmetric mode

Return type:: float

virtual valuesRequired(self) → bool[source]¶

Returns if the method requires values to calculate the classes If not, bounds are sufficient

Return type:: bool

virtual writeXml(self, element: QDomElement, context: QgsReadWriteContext)[source]¶

Writes extra information about the method

Parameters:

element (QDomElement)
context (QgsReadWriteContext)