store QgsVectorLayer.getFeatures() result in order to speed up subsequent feature requests

Question

I'm doing a lot (really a lot) of feature requests on a vector layer. These requests are capsuled in iterations and functions, so no way of reducing the total number of requests.

Although I consider the #1 tip concerning QgsVectorLayer.getFeatures() - use a specific request whenever possible (Why use QgsFeatureRequest() when iterating?) - I end up with low performance and cProfile tells me the bottleneck is still the feature request.

Btw, using layer.getFeature(fid) instead of

request = QgsFeatureRequest().setFilterFid(fid)
feature = next(layer.getFeatures(request))

doesn't make any difference.

How do I speed up my feature requests, when I know each feature is called lots of times?

Answer 1

My solution is a dictionary called lineIndex, with the format {fid: QgsFeature}:

self.lineIndex={}
lines = layer.getFeatures()
for line in lines:  # every line
    self.lineIndex[line.id()] = line

Now I can acess any feature in no time by feat = self.lineIndex[fid].

For more complex questions, tuples as dictionary keys could be considered (https://codereview.stackexchange.com/questions/205141/search-dictionary-for-matching-values).