How to import a STL file using the file browser?

Question

I'm trying to import a stl file manually via python. My code below is pretty straight forward, but I'm struggling with the following line. I'm not sure about the syntax and format of the arguments:

bpy.ops.import_mesh.stl(filepath=???, files=???)

The current state of my operator:

import bpy

class FILE_OT_import_stl(bpy.types.Operator):

    bl_idname = "file.import_model_stl"
    bl_label = "Import Model STL"
    bl_options = {'REGISTER', 'UNDO'} # Must have REGISTER!   

    def execute(self, context):
        #my_filepath = 'K:/PQJ/Mold Generator/Blender test/'
        #filepath = '//898L-OutputModel-SLA[]_09'
        #print(filepath)
        all_files=[bpy.types.Scene.import_path]
        #print(file[0])
        bpy.ops.import_mesh.stl(filepath=my_filepath, files=all_files)
        return {'FINISHED'}

class FILE_PANEL_PT_import_export(bpy.types.Panel):
    bl_label = "Import/Export"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    # bl_context = "object" # object vs edit mode

    def draw(self, context):
        layout = self.layout
        layout.label(text="Import")
               
        layout.prop(context.scene, "import_path")
        row = layout.row()                
        row.operator("file.import_model_stl")

classes = (
    FILE_OT_import_stl,
    FILE_PANEL_PT_import_export
)

def register():
    for cls in classes:
        bpy.types.Scene.import_path = bpy.props.StringProperty(name='Import path', subtype='FILE_PATH')
        bpy.utils.register_class(cls)

def unregister():
    del bpy.types.Scene.import_path
    for cls in classes:
        bpy.utils.unregister_class(cls)

if __name__ == "__main__":
    register()

Q: How to import a certain STL file using the file browser (and add a custom material)?

Answer 1

You can just add the built-in operator import_mesh.stl to your draw method of your panel which will open up the File Browser as usual and allows the user to select one .stl file:

import bpy

class OBJECT_PT_CustomPanel(bpy.types.Panel):
    bl_label = "My Panel"
    bl_idname = "OBJECT_PT_custom_panel"
    bl_space_type = "VIEW_3D"   
    bl_region_type = "UI"
    bl_category = "Tools"
    bl_context = "objectmode"

    def draw(self, context):
        layout = self.layout
        #layout.operator_context = 'INVOKE_DEFAULT' #'INVOKE_AREA'
        layout.operator("import_mesh.stl", text="New", icon='FILE_NEW')

def register():
    bpy.utils.register_class(OBJECT_PT_CustomPanel)

def unregister():
    bpy.utils.unregister_class(OBJECT_PT_CustomPanel)

if __name__ == "__main__":
    register()

Related: How to call a confirmation dialog box?

---

In case you want to import and modify the .stl object for whatever reason, have a look into the Operator File Import template (operator_file_import.py) that comes with Blender.

Demo operator based on the template, allows to import the file, print the object reference and assigns a new material to the incoming object in one go:

# ImportHelper is a helper class, defines filename and
# invoke() function which calls the file selector.
from bpy_extras.io_utils import ImportHelper
from bpy.types import Operator

class ImportSomeData(Operator, ImportHelper):
    """This appears in the tooltip of the operator and in the generated docs"""
    bl_idname = "import_test.some_data"
    bl_label = "Import Some Stl File"
    bl_options = {'REGISTER', 'UNDO'}
    
    # ImportHelper mixin class uses this
    filename_ext = ".stl"
    filter_glob: bpy.props.StringProperty(
                default="*.stl",
                options={'HIDDEN'})
                
    def execute(self, context):
        if self.filepath:
            bpy.ops.import_mesh.stl(filepath=self.filepath)
            # Print the imported object reference
            print ("Imported object:", context.object)
            # Create a material
            mat = bpy.data.materials.new(name="STLMaterial")
            # Append the material to the last slot
            context.object.data.materials.append(mat)

        return {'FINISHED'}

Further reading:

• How to assign a new material to an object in the scene from Python?
• Import multiple STL files and modify the incoming objects in one go?