Importing multiple files in blender import plugin

I'm writing an import plugin for blender 2.8x and I'd like to make use of the multiple file selection feature. Unfortunately, I can't find any provision for this in 'ImportHelper' (the class I derive from) and web searches haven't yielded anything that seems to work and I can't seem to find anything in the documentation either.

As explained in Luther's answer, you need to add a files : CollectionProperty attribute to your class to enable multifile support.

However, in addition you also need a directory: StringProperty attribute. Then you need to build the full filepath using os.path.join.

See below for the code from a complete working import addon that supports multifile import. It is a modification of the "Operator File Import" template (operator_file_import.py). The code was tested on Blender 3.4.1.

operator_file_import.multiple.py :

import os
import bpy

def read_some_data(context, filepath, use_some_setting):
    print("Importing:", filepath)
    f = open(filepath, 'r', encoding='utf-8')
    try:
      data = f.read() # Fails on some latin-1 encoded text files, but not relevant to this importer example.
    except:
      pass
    f.close()

    # would normally load the data here
    #print(data)

    return {'FINISHED'}


# ImportHelper is a helper class, defines filename and
# invoke() function which calls the file selector.
from bpy_extras.io_utils import ImportHelper
from bpy.props import StringProperty, BoolProperty, EnumProperty, CollectionProperty
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"  # important since its how bpy.ops.import_test.some_data is constructed
    bl_label = "Import Some Data"

    # ImportHelper mixin class uses this
    filename_ext = ".txt"

    filter_glob: StringProperty(
        default="*.txt",
        options={'HIDDEN'},
        maxlen=255,  # Max internal buffer length, longer would be clamped.
    )

    # List of operator properties, the attributes will be assigned
    # to the class instance from the operator settings before calling.
    use_setting: BoolProperty(
        name="Example Boolean",
        description="Example Tooltip",
        default=True,
    )

    type: EnumProperty(
        name="Example Enum",
        description="Choose between two items",
        items=(
            ('OPT_A', "First Option", "Description one"),
            ('OPT_B', "Second Option", "Description two"),
        ),
        default='OPT_A',
    )

    ###########################################
    # necessary to support multi-file import
    files: CollectionProperty(
        type=bpy.types.OperatorFileListElement,
        options={'HIDDEN', 'SKIP_SAVE'},
    )

    directory: StringProperty(
        subtype='DIR_PATH',
    )
    ###########################################

    def execute(self, context):
        for current_file in self.files:
            filepath = os.path.join(self.directory, current_file.name)
            read_some_data(context, filepath, self.use_setting)
        return {'FINISHED'}


# Only needed if you want to add into a dynamic menu.
def menu_func_import(self, context):
    self.layout.operator(ImportSomeData.bl_idname, text="Text Import Operator")


# Register and add to the "file selector" menu (required to use F3 search "Text Import Operator" for quick access).
def register():
    bpy.utils.register_class(ImportSomeData)
    bpy.types.TOPBAR_MT_file_import.append(menu_func_import)


def unregister():
    bpy.utils.unregister_class(ImportSomeData)
    bpy.types.TOPBAR_MT_file_import.remove(menu_func_import)


if __name__ == "__main__":
    register()

    # test call
    bpy.ops.import_test.some_data('INVOKE_DEFAULT')

These are the relevant changes to the basic import template:

1. Import os to use os.path.join:

   import os
   

2. Import CollectionProperty:

   from bpy.props import StringProperty, BoolProperty, EnumProperty, CollectionProperty
   

3. Add the files and directory properties:

   ###########################################
   # necessary to support multi-file import
   files: CollectionProperty(
       type=bpy.types.OperatorFileListElement,
       options={'HIDDEN', 'SKIP_SAVE'},
   )
   
   directory: StringProperty(
       subtype='DIR_PATH',
   )
   ###########################################
   

4. Loop through self.files and build the full paths using os.path.join:

   def execute(self, context):
       for current_file in self.files:
           filepath = os.path.join(self.directory, current_file.name)
           read_some_data(context, filepath, self.use_setting)
       return {'FINISHED'}