Accessing list of keyframes for blend shape animations

[Paul Thurston]

Hey y'all, I am currently writing a tool that exports animation data to a text file. It needs to only export data on their keyframes not every frame. Currently I can get a list of keyframes for transform data by using maya.cmds.keyframe() and get the values by using maya.cmds.getAttr(), but this method does not work for blend shape animations. Does anyone know of a good method to get a list of blend shape keyframes for a given object?

Sorry if this is a duplicate, I posted once but couldn't find the post later so I couldn't tell if it went through.

Thanks,
Paul