[processing] Add API to convert a parameter definition to an equivalent

Python constructor string

Author: nyalldawson

python/core/auto_generated/processing/qgsprocessing.sip.in

@@ -39,6 +39,11 @@ and parameters.
       TypeMesh
     };
 
+    enum PythonOutputType
+    {
+      PythonQgsProcessingAlgorithmSubclass,
+    };
+
     static QString sourceTypeToString( SourceType type );
 %Docstring
 Converts a source ``type`` to a string representation.

python/core/auto_generated/processing/qgsprocessingparameters.sip.in

@@ -303,7 +303,18 @@ The returned value must be correctly escaped - e.g. string values must be wrappe
     virtual QString asScriptCode() const;
 %Docstring
 Returns the parameter definition encoded in a string which can be used within a
-Python processing script.
+Processing script.
+%End
+
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+%Docstring
+Returns the parameter definition as a Python command which can be used within a
+Python Processing script.
+
+The ``outputType`` argument specifies the desired output format for the Python string,
+i.e. the intended end use of the generated Python code.
+
+.. versionadded:: 3.6
 %End
 
     virtual QVariantMap toVariantMap() const;
@@ -1172,6 +1183,8 @@ Returns the type name for the parameter class.
 
     virtual QString asScriptCode() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     Behavior behavior() const;
 %Docstring
@@ -1245,6 +1258,8 @@ Returns the type name for the parameter class.
 
     virtual QString valueAsPythonString( const QVariant &value, QgsProcessingContext &context ) const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     QStringList headers() const;
 %Docstring
@@ -1343,6 +1358,8 @@ Returns the type name for the parameter class.
 
     virtual QString asScriptCode() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     QgsProcessing::SourceType layerType() const;
 %Docstring
@@ -1440,6 +1457,8 @@ Returns the type name for the parameter class.
 
     virtual QString toolTip() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     double minimum() const;
 %Docstring
@@ -1542,6 +1561,8 @@ Returns the type name for the parameter class.
 
     virtual QStringList dependsOnOtherParameters() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     QString parentParameterName() const;
 %Docstring
@@ -1614,6 +1635,8 @@ Returns the type name for the parameter class.
 
     virtual QString valueAsPythonString( const QVariant &value, QgsProcessingContext &context ) const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     QgsProcessingParameterNumber::Type dataType() const;
 %Docstring
@@ -1713,6 +1736,8 @@ Returns the type name for the parameter class.
 
     virtual QString asScriptCode() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     QStringList options() const;
 %Docstring
@@ -1785,6 +1810,8 @@ Returns the type name for the parameter class.
 
     virtual QString asScriptCode() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     bool multiLine() const;
 %Docstring
@@ -1887,6 +1914,8 @@ Returns the type name for the parameter class.
 
     virtual QStringList dependsOnOtherParameters() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     QString parentLayerParameterName() const;
 %Docstring
@@ -1985,6 +2014,8 @@ Returns the type name for the parameter class.
 
     virtual QString valueAsPythonString( const QVariant &value, QgsProcessingContext &context ) const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     virtual QVariantMap toVariantMap() const;
 
@@ -2080,6 +2111,8 @@ Returns the type name for the parameter class.
 
     virtual QString asScriptCode() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
     virtual QStringList dependsOnOtherParameters() const;
 
 
@@ -2171,6 +2204,8 @@ Returns the type name for the parameter class.
 
     virtual QString asScriptCode() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     virtual QVariantMap toVariantMap() const;
 
@@ -2212,6 +2247,8 @@ output will not be created by default.
 
     virtual bool fromVariantMap( const QVariantMap &map );
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     virtual QgsProcessingOutputDefinition *toOutputDefinition() const = 0 /Factory/;
 %Docstring
@@ -2321,6 +2358,8 @@ Returns the type name for the parameter class.
 
     virtual QString defaultFileExtension() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     virtual QStringList supportedOutputVectorLayerExtensions() const;
 %Docstring
@@ -2411,6 +2450,8 @@ Returns the type name for the parameter class.
 
     virtual QString defaultFileExtension() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     virtual QStringList supportedOutputVectorLayerExtensions() const;
 %Docstring
@@ -2551,6 +2592,8 @@ Returns the type name for the parameter class.
 
     virtual QString defaultFileExtension() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     QString fileFilter() const;
 %Docstring
@@ -2658,6 +2701,8 @@ Returns the type name for the parameter class.
 
     virtual QStringList dependsOnOtherParameters() const;
 
+    virtual QString asPythonString( QgsProcessing::PythonOutputType outputType = QgsProcessing::PythonQgsProcessingAlgorithmSubclass ) const;
+
 
     QString parentLayerParameterName() const;
 %Docstring

src/core/processing/models/qgsprocessingmodelalgorithm.cpp

@@ -23,6 +23,7 @@
 #include "qgsexception.h"
 #include "qgsvectorlayer.h"
 #include "qgsapplication.h"
+#include "qgsprocessingparametertype.h"
 
 #include <QFile>
 #include <QTextStream>

src/core/processing/qgsprocessing.h

@@ -54,6 +54,12 @@ class CORE_EXPORT QgsProcessing
       TypeMesh = 6 //!< Mesh layers \since QGIS 3.6
     };
 
+    //! Available Python output types
+    enum PythonOutputType
+    {
+      PythonQgsProcessingAlgorithmSubclass, //!< Full Python QgsProcessingAlgorithm subclass
+    };
+
     /**
      * Converts a source \a type to a string representation.
      *