Proper use of foreach_set

foreach_set is a convenient wrapper in the Blender Python API for quickly setting the desired value for each element of the bpy_prop_collection type. However, when using this function, script developers sometimes run into an error.

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For example, let’s switch all the polygons in the mesh to smooth shading. To achieve this, the “use_smooth” property of each mesh polygon must be set to True.

With common Python syntax, we can write the following code:

If we want to use the foreach_set functional, it seems logical to write the following:

however, calling this function in this way will result in an error:

couldn’t access the py sequence

This occurs because the second parameter in the foreach_set function should not be the value itself, which we want to set for the “use_smooth” property, but a list of values ​​for each of the polygons.

Instead of

we need to use:

The length of the list must correspond to the number of elements for which the foreach_set function is called, in our case – the number of polygons.

So, to properly use the foreach_set function, first we need to create a list of values ​​by the number of mesh polygons:

and next pass it as the second parameter to the function:

Or all in one string: