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Make sure that bool(obj) is True for QGIS API objects

bool(obj) in Python has the following semantics:
1. if the object has __bool__() method, return its value
2. if the object has __len__() method, return its value
3. return True

So for objects in QGIS API that implement __len__() method, we were getting
unexpected behavior - for example, "if layer: ..." would evaluate as False
in case the layer was empty, while the usual expectation is that any reference
to an object that is not None should evaluate to True.
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wonder-sk committed Jun 22, 2018
1 parent fb9e575 commit 4c8b801791af0588d5a78793f59c11725c16e9d4
@@ -69,6 +69,12 @@ if the feature count is unknown.
sipRes = sipCpp->featureCount();
%End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
%MethodCode
sipRes = true;
%End

virtual long featureCount() const = 0;
%Docstring
Returns the number of features contained in the source, or -1
@@ -74,6 +74,12 @@ Returns the number of features contained in the store.
sipRes = sipCpp->count();
%End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
%MethodCode
sipRes = true;
%End

QgsFeatureList features() const;
%Docstring
Returns the list of features contained in the store.
@@ -103,6 +103,12 @@ Returns number of items
sipRes = sipCpp->count();
%End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
%MethodCode
sipRes = true;
%End

int size() const;
%Docstring
Returns number of items
@@ -46,6 +46,12 @@ Returns the number of layers contained in the store.
sipRes = sipCpp->count();
%End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
%MethodCode
sipRes = true;
%End

QgsMapLayer *mapLayer( const QString &id ) const;
%Docstring
Retrieve a pointer to a layer by layer ``id``.
@@ -221,6 +221,12 @@ if the feature count is unknown.
sipRes = sipCpp->featureCount();
%End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
%MethodCode
sipRes = true;
%End

long featureCount() const;
%Docstring
Returns the number of features contained in the source, or -1
@@ -93,6 +93,12 @@ class CORE_EXPORT QgsFeatureSource
% MethodCode
sipRes = sipCpp->featureCount();
% End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
% MethodCode
sipRes = true;
% End
#endif

/**
@@ -79,6 +79,12 @@ class CORE_EXPORT QgsFeatureStore : public QgsFeatureSink
% MethodCode
sipRes = sipCpp->count();
% End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
% MethodCode
sipRes = true;
% End
#endif

/**
@@ -133,6 +133,12 @@ class CORE_EXPORT QgsFields
% MethodCode
sipRes = sipCpp->count();
% End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
% MethodCode
sipRes = true;
% End
#endif

//! Returns number of items
@@ -59,6 +59,12 @@ class CORE_EXPORT QgsMapLayerStore : public QObject
% MethodCode
sipRes = sipCpp->count();
% End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
% MethodCode
sipRes = true;
% End
#endif

/**
@@ -276,6 +276,12 @@ class CORE_EXPORT QgsVectorLayerCache : public QObject
% MethodCode
sipRes = sipCpp->featureCount();
% End

//! Ensures that bool(obj) returns true (otherwise __len__() would be used)
int __bool__() const;
% MethodCode
sipRes = true;
% End
#endif

/**

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