mirror of
https://github.com/qgis/QGIS.git
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508 lines
15 KiB
Plaintext
508 lines
15 KiB
Plaintext
/************************************************************************
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* This file has been generated automatically from *
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* *
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* src/core/expression/qgsexpression.h *
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* *
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* Do not edit manually ! Edit header and run scripts/sipify.pl again *
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************************************************************************/
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class QgsExpression
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{
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%Docstring
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Class for parsing and evaluation of expressions (formerly called "search strings").
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The expressions try to follow both syntax and semantics of SQL expressions.
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Usage:
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\code{.cpp}
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QgsExpression exp("gid*2 > 10 and type not in ('D','F'));
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if (exp.hasParserError())
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{
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// show error message with parserErrorString() and exit
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}
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QVariant result = exp.evaluate(feature, fields);
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if (exp.hasEvalError())
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{
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// show error message with evalErrorString()
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}
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else
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{
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// examine the result
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}
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\endcode
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Three Value Logic
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=================
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Similarly to SQL, this class supports three-value logic: true/false/unknown.
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Unknown value may be a result of operations with missing data (NULL). Please note
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that NULL is different value than zero or an empty string. For example
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3 > NULL returns unknown.
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There is no special (three-value) 'boolean' type: true/false is represented as
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1/0 integer, unknown value is represented the same way as NULL values: NULL QVariant.
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Performance
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===========
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For better performance with many evaluations you may first call prepare(fields) function
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to find out indices of columns and then repeatedly call evaluate(feature).
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Type conversion
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===============
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Operators and functions that expect arguments to be of a particular
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type automatically convert the arguments to that type, e.g. sin('2.1') will convert
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the argument to a double, length(123) will first convert the number to a string.
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Explicit conversion can be achieved with to_int, to_real, to_string functions.
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If implicit or explicit conversion is invalid, the evaluation returns an error.
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Comparison operators do numeric comparison in case both operators are numeric (int/double)
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or they can be converted to numeric types.
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Implicit sharing
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================
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This class is implicitly shared, copying has a very low overhead.
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It is normally preferable to call `QgsExpression( otherExpression )` instead of
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`QgsExpression( otherExpression.expression() )`. A deep copy will only be made
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when prepare() is called. For usage this means mainly, that you should
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normally keep an unprepared master copy of a QgsExpression and whenever using it
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with a particular QgsFeatureIterator copy it just before and prepare it using the
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same context as the iterator.
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Implicit sharing was added in 2.14
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%End
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%TypeHeaderCode
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#include "qgsexpression.h"
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%End
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public:
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QgsExpression( const QString &expr );
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%Docstring
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Creates a new expression based on the provided string.
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The string will immediately be parsed. For optimization
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prepare() should always be called before every
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loop in which this expression is used.
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%End
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QgsExpression( const QgsExpression &other );
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%Docstring
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Create a copy of this expression. This is preferred
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over recreating an expression from a string since
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it does not need to be re-parsed.
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%End
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QgsExpression();
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%Docstring
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Create an empty expression.
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.. versionadded:: 3.0
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%End
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~QgsExpression();
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bool operator==( const QgsExpression &other ) const;
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bool isValid() const;
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%Docstring
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Checks if this expression is valid.
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A valid expression could be parsed but does not necessarily evaluate properly.
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.. versionadded:: 3.0
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:rtype: bool
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%End
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bool hasParserError() const;
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%Docstring
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Returns true if an error occurred when parsing the input expression
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:rtype: bool
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%End
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QString parserErrorString() const;
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%Docstring
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Returns parser error
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:rtype: str
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%End
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const QgsExpressionNode *rootNode() const;
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%Docstring
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Returns root node of the expression. Root node is null is parsing has failed
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:rtype: QgsExpressionNode
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%End
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bool prepare( const QgsExpressionContext *context );
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%Docstring
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Get the expression ready for evaluation - find out column indexes.
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\param context context for preparing expression
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.. versionadded:: 2.12
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:rtype: bool
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%End
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QSet<QString> referencedColumns() const;
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%Docstring
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Get list of columns referenced by the expression.
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.. note::
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If the returned list contains the QgsFeatureRequest.AllAttributes constant then
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all attributes from the layer are required for evaluation of the expression.
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QgsFeatureRequest.setSubsetOfAttributes automatically handles this case.
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.. seealso:: referencedAttributeIndexes()
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:rtype: set of str
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%End
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QSet<QString> referencedVariables() const;
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%Docstring
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Return a list of all variables which are used in this expression.
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If the list contains a NULL QString, there is a variable name used
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which is determined at runtime.
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.. versionadded:: 3.0
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:rtype: set of str
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%End
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QSet<int> referencedAttributeIndexes( const QgsFields &fields ) const;
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%Docstring
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Return a list of field name indexes obtained from the provided fields.
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.. versionadded:: 3.0
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:rtype: set of int
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%End
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bool needsGeometry() const;
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%Docstring
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Returns true if the expression uses feature geometry for some computation
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:rtype: bool
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%End
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QVariant evaluate();
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%Docstring
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Evaluate the feature and return the result.
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.. note::
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this method does not expect that prepare() has been called on this instance
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.. versionadded:: 2.12
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:rtype: QVariant
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%End
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QVariant evaluate( const QgsExpressionContext *context );
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%Docstring
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Evaluate the expression against the specified context and return the result.
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\param context context for evaluating expression
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.. note::
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prepare() should be called before calling this method.
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.. versionadded:: 2.12
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:rtype: QVariant
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%End
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bool hasEvalError() const;
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%Docstring
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Returns true if an error occurred when evaluating last input
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:rtype: bool
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%End
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QString evalErrorString() const;
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%Docstring
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Returns evaluation error
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:rtype: str
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%End
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void setEvalErrorString( const QString &str );
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%Docstring
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Set evaluation error (used internally by evaluation functions)
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%End
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bool isField() const;
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%Docstring
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Checks whether an expression consists only of a single field reference
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.. versionadded:: 2.9
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:rtype: bool
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%End
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static bool checkExpression( const QString &text, const QgsExpressionContext *context, QString &errorMessage /Out/ );
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%Docstring
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Tests whether a string is a valid expression.
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\param text string to test
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\param context optional expression context
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\param errorMessage will be filled with any error message from the validation
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:return: true if string is a valid expression
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.. versionadded:: 2.12
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:rtype: bool
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%End
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void setExpression( const QString &expression );
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%Docstring
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Set the expression string, will reset the whole internal structure.
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.. versionadded:: 3.0
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%End
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QString expression() const;
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%Docstring
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API calls, dump() will be used to create one instead.
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:rtype: str
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%End
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QString dump() const;
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%Docstring
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expression() instead.
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:rtype: str
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%End
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QgsDistanceArea *geomCalculator();
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%Docstring
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Return calculator used for distance and area calculations
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(used by $length, $area and $perimeter functions only)
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.. seealso:: setGeomCalculator()
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.. seealso:: distanceUnits()
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.. seealso:: areaUnits()
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:rtype: QgsDistanceArea
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%End
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void setGeomCalculator( const QgsDistanceArea *calc );
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%Docstring
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Sets the geometry calculator used for distance and area calculations in expressions.
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(used by $length, $area and $perimeter functions only). By default, no geometry
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calculator is set and all distance and area calculations are performed using simple
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cartesian methods (ie no ellipsoidal calculations).
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\param calc geometry calculator. Ownership is not transferred. Set to a None to force
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cartesian calculations.
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.. seealso:: geomCalculator()
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%End
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QgsUnitTypes::DistanceUnit distanceUnits() const;
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%Docstring
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Returns the desired distance units for calculations involving geomCalculator(), e.g., "$length" and "$perimeter".
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.. note::
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distances are only converted when a geomCalculator() has been set
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.. versionadded:: 2.14
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.. seealso:: setDistanceUnits()
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.. seealso:: areaUnits()
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:rtype: QgsUnitTypes.DistanceUnit
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%End
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void setDistanceUnits( QgsUnitTypes::DistanceUnit unit );
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%Docstring
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Sets the desired distance units for calculations involving geomCalculator(), e.g., "$length" and "$perimeter".
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.. note::
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distances are only converted when a geomCalculator() has been set
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.. versionadded:: 2.14
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.. seealso:: distanceUnits()
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.. seealso:: setAreaUnits()
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%End
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QgsUnitTypes::AreaUnit areaUnits() const;
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%Docstring
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Returns the desired areal units for calculations involving geomCalculator(), e.g., "$area".
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.. note::
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areas are only converted when a geomCalculator() has been set
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.. versionadded:: 2.14
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.. seealso:: setAreaUnits()
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.. seealso:: distanceUnits()
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:rtype: QgsUnitTypes.AreaUnit
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%End
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void setAreaUnits( QgsUnitTypes::AreaUnit unit );
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%Docstring
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Sets the desired areal units for calculations involving geomCalculator(), e.g., "$area".
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.. note::
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areas are only converted when a geomCalculator() has been set
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.. versionadded:: 2.14
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.. seealso:: areaUnits()
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.. seealso:: setDistanceUnits()
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%End
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static QString replaceExpressionText( const QString &action, const QgsExpressionContext *context,
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const QgsDistanceArea *distanceArea = 0 );
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%Docstring
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This function replaces each expression between [% and %]
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in the string with the result of its evaluation with the specified context
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Additional substitutions can be passed through the substitutionMap parameter
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\param action The source string in which placeholders should be replaced.
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\param context Expression context
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\param distanceArea Optional QgsDistanceArea. If specified, the QgsDistanceArea is used for distance
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and area conversion
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.. versionadded:: 2.12
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:rtype: str
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%End
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static double evaluateToDouble( const QString &text, const double fallbackValue );
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%Docstring
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Attempts to evaluate a text string as an expression to a resultant double
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value.
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\param text text to evaluate as expression
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\param fallbackValue value to return if text can not be evaluated as a double
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:return: evaluated double value, or fallback value
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.. versionadded:: 2.7
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.. note::
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this method is inefficient for bulk evaluation of expressions, it is intended
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for one-off evaluations only.
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:rtype: float
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%End
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enum SpatialOperator
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{
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soBbox,
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soIntersects,
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soContains,
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soCrosses,
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soEquals,
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soDisjoint,
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soOverlaps,
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soTouches,
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soWithin,
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};
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static const QList<QgsExpressionFunction *> &Functions();
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%Docstring
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:rtype: list of QgsExpressionFunction
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%End
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static const QStringList &BuiltinFunctions();
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%Docstring
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:rtype: list of str
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%End
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static bool registerFunction( QgsExpressionFunction *function, bool transferOwnership = false );
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%Docstring
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Registers a function to the expression engine. This is required to allow expressions to utilize the function.
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\param function function to register
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\param transferOwnership set to true to transfer ownership of function to expression engine
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:return: true on successful registration
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.. seealso:: unregisterFunction
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:rtype: bool
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%End
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static bool unregisterFunction( const QString &name );
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%Docstring
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Unregisters a function from the expression engine. The function will no longer be usable in expressions.
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\param name function name
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.. seealso:: registerFunction
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:rtype: bool
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%End
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static void cleanRegisteredFunctions();
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%Docstring
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Deletes all registered functions whose ownership have been transferred to the expression engine.
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.. versionadded:: 2.12
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%End
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static bool isFunctionName( const QString &name );
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%Docstring
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tells whether the identifier is a name of existing function
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:rtype: bool
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%End
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static int functionIndex( const QString &name );
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%Docstring
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return index of the function in Functions array
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:rtype: int
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%End
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static int functionCount();
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%Docstring
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Returns the number of functions defined in the parser
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:return: The number of function defined in the parser.
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:rtype: int
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%End
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static QString quotedColumnRef( QString name );
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%Docstring
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Returns a quoted column reference (in double quotes)
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.. seealso:: quotedString()
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.. seealso:: quotedValue()
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:rtype: str
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%End
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static QString quotedString( QString text );
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%Docstring
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Returns a quoted version of a string (in single quotes)
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.. seealso:: quotedValue()
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.. seealso:: quotedColumnRef()
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:rtype: str
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%End
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static QString quotedValue( const QVariant &value );
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%Docstring
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Returns a string representation of a literal value, including appropriate
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quotations where required.
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\param value value to convert to a string representation
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.. versionadded:: 2.14
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.. seealso:: quotedString()
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.. seealso:: quotedColumnRef()
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:rtype: str
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%End
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static QString quotedValue( const QVariant &value, QVariant::Type type );
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%Docstring
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Returns a string representation of a literal value, including appropriate
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quotations where required.
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\param value value to convert to a string representation
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\param type value type
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.. versionadded:: 2.14
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.. seealso:: quotedString()
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.. seealso:: quotedColumnRef()
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:rtype: str
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%End
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static QString helpText( QString name );
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%Docstring
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Returns the help text for a specified function.
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\param name function name
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.. seealso:: variableHelpText()
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:rtype: str
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%End
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static QString variableHelpText( const QString &variableName, bool showValue = true, const QVariant &value = QVariant() );
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%Docstring
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Returns the help text for a specified variable.
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\param variableName name of variable
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\param showValue set to true to include current value of variable in help text
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\param value current value of variable to show in help text
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.. seealso:: helpText()
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.. versionadded:: 2.12
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:rtype: str
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%End
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static QString group( const QString &group );
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%Docstring
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Returns the translated name for a function group.
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\param group untranslated group name
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:rtype: str
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%End
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static QString formatPreviewString( const QVariant &value );
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%Docstring
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Formats an expression result for friendly display to the user. Truncates the result to a sensible
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length, and presents text representations of non numeric/text types (e.g., geometries and features).
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\param value expression result to format
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:return: formatted string, may contain HTML formatting characters
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.. versionadded:: 2.14
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:rtype: str
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%End
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};
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/************************************************************************
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* This file has been generated automatically from *
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* *
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* src/core/expression/qgsexpression.h *
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* *
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* Do not edit manually ! Edit header and run scripts/sipify.pl again *
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************************************************************************/
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