Auto-install missing python modules

pip_meta_path_finder.py

import sys
import pip

from importlib import import_module
from importlib.abc import MetaPathFinder

class PipMetaPathFinder(MetaPathFinder):
    """A importlib.abc.MetaPathFinder to auto-install missing modules using pip
    """
    def find_spec(fullname, path, target=None):
        if path == None: 
            installed = pip.main(['install', fullname])
            if installed == 0:
                return import_module(fullname)

sys.meta_path.append(PipMetaPathFinder)

My python compiler is saying that Attribution error: 'list' object has no attribute 'append'