‘str’ object has no attribute ‘stringByAppendingString_’

Has something changed here? I am getting this error when using GSInstance.generate() now:

File "GlyphsApp/GlyphsApp/__init__.py", line 7063, in __GSInstance_Export__
  File "GlyphsApp/GlyphsApp/__init__.py", line 6966, in collectResult_instance_title_
AttributeError: 'str' object has no attribute 'stringByAppendingString_'

Make sure it is an NSString, not str. What was your code?

This is Glyphs’s job. It works fine in 3408. The documentation also says that the expected type is str, not NSString: https://docu.glyphsapp.com/#GSInstance.generate

My code was simply:

instance.generate(
			format=flavour,  # str
			fontPath=directory,  # str
			removeOverlap=remove_overlap,  # bool
			autoHint=autohint,  # bool
			containers=[container]  # List[string]
		)

I have fixed that.

Thanks!