[Qgis-user] pyQGIS - set attributes by expression

[Nyall Dawson]

On Wed, 6 Feb 2019 at 00:37, Wouter Impens <wouter.impens at gmail.com> wrote:
>
> Hi,
>
> Hope anyone can help me with this:
>
> I'm trying to iterate over the fields of a vector layer (using the index) and fill in the values by an expression
>
>  my_features = a_layer.getFeatures()
>     for a_feat in my_features:
>         mijn_index = a_feat.fieldNameIndex('perc_nr')
>         value = an_expr

What's "an_expr" here? Is it a QgsExpression object?

Nyall

>          a_feat.setAttribute(mijn_index, value)
>
>     a_layer.commitChanges()
>
> I don't get an error but nothing is filled in. I evaluated the expression and it's true. It also works in the field calculator.
>
> Anyone an idea?
>
>
> Kind regards
> Wouter
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