Adding double typed PyQGIS vector attributes to layer

Question

I am trying to create a new vector memory layer with attribute data populated as follows and cannot figure out why it works with integer or string typed data but silently does not populate any rows with double typed data.

def create_layer(columns: List[QgsField], data: List[Tuple]):
   layer = QgsVectorLayer('multipoint?crs=epsg:3347', "TEST", "memory")
   provider = layer.dataProvider()
   provider.addAttributes(columns)
   with edit(layer):
      for row in data:
         wkb, attrs = row[0], row[1:]
         geom = QgsGeometry()
         geom.fromWkb(bytearray(wkb))
         feature = QgsFeature()
         feature.setGeometry(geom)
         feature.setAttributes(list(attrs))
         provider.addFeatures([feature])
   return layer

assert create_layer(
   columns=[QgsField('weight', QVariant.Int)],
   data=list(zip(my_geoms, [int(w) for w in my_weights]))
).featureCount() > 0   # PASS

assert create_layer(
   columns=[QgsField('weight', QVariant.String)],
   data=list(zip(my_geoms, [str(w) for w in my_weights]))
).featureCount() > 0   # PASS

assert create_layer(
   columns=[QgsField('weight', QVariant.Double)],  # also tried QgsField('weight', QVariant.Double, 'double' , 8, 6)
   data=list(zip(my_geoms, [round(w, 2) for w in my_weights]))
).featureCount() > 0     # FAILS!

(The length of my_geoms & my_weights are the same & the values of my_weights are Python floats)

Answer 1

I am not sure if it works (because I couldn't produce the same issue), but sometimes you need to cast the value to float. So, try:

data=list(zip(my_geoms, [round(float(w), 2) for w in my_weights]))

or maybe:

data=list(zip(my_geoms, [float(round(w, 2)) for w in my_weights]))

Answer 2

As I could not see any obvious error in your code, I have implemented some code to test your implementation using QGIS 3.16.11. For the sake of simplicity, and as this seemed not the source of the issue, I tested using NULL geometry (i.e., commented out the call to geom.fromWkb(bytearray(wkb)) in create_layer(). The function test_create_layer() checks the number of features available in the vector layer and prints out the type and value of attributes of each feature:

def create_layer(columns, data):
   layer = QgsVectorLayer('multipoint?crs=epsg:3347', "TEST", "memory")
   provider = layer.dataProvider()
   provider.addAttributes(columns)
   with edit(layer):
      for row in data:
         wkb, attrs = row[0], row[1:]
         geom = QgsGeometry()
         #geom.fromWkb(bytearray(wkb))
         feature = QgsFeature()
         feature.setGeometry(geom)
         feature.setAttributes(list(attrs))
         provider.addFeatures([feature])
   return layer

def test_create_layer(columns_, data_):
    layer = create_layer(columns=columns_, data=data_)
    assert layer.featureCount() == len(data_)
    for f in layer.getFeatures():
        print(f"{f.id()}: {','.join([f'{type(el)}-{str(el)}' for el in f.attributes()])}")

my_geoms = [None, None, None, None] 
my_weights = [1.11111, 2.22222, 3.33333, 4.44444]

test_create_layer([QgsField('weight', QVariant.Int)], list(zip(my_geoms, [int(w) for w in my_weights])))
test_create_layer([QgsField('weight', QVariant.String)], list(zip(my_geoms, [str(w) for w in my_weights])))
test_create_layer([QgsField('weight', QVariant.Double)], list(zip(my_geoms, [round(w, 2) for w in my_weights])))

The code executes successfully and the following output is produced: Overall, the code works fine in my case. Maybe something in my_weights or my_geoms causes the issue at your end.