Process multi files (ImportHelper) in blender.

process_files.py

import bpy

def process_files(context, directory, files):
    import os
    for file in files:
        path = os.path.join(directory, file.name)
        print("process %s" % path)
    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, CollectionProperty
from bpy.types import Operator, OperatorFileListElement


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.
            )

    files = CollectionProperty(
        name="BVH files",
        type=OperatorFileListElement,
        )

    directory = StringProperty(subtype='DIR_PATH')

    def execute(self, context):
        return process_files(context, self.directory, self.files)


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

def register():
    bpy.utils.register_class(ImportSomeData)
    bpy.types.INFO_MT_file_import.append(menu_func_import)

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


if __name__ == "__main__":
    register()

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