之前使用某虚拟环境配置Django时已经把各种Mysql的包都装好了，项目也成功开发完了一个，后来开发第二个项目时改将sqlite改为mysql后又诡异地报错了：

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Applications/PyCharm.app/Contents/helpers/pycharm/_jb_manage_tasks_provider.py", line 25, in <module>
    django.setup()
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/apps/registry.py", line 112, in populate
    app_config.import_models()
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/apps/config.py", line 198, in import_models
    self.models_module = import_module(models_module_name)
  File "/Users/apple/Documents/article/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/contrib/auth/models.py", line 2, in <module>
    from django.contrib.auth.base_user import AbstractBaseUser, BaseUserManager
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/contrib/auth/base_user.py", line 47, in <module>
    class AbstractBaseUser(models.Model):
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/db/models/base.py", line 114, in __new__
    new_class.add_to_class('_meta', Options(meta, app_label))
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/db/models/base.py", line 315, in add_to_class
    value.contribute_to_class(cls, name)
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/db/models/options.py", line 205, in contribute_to_class
    self.db_table = truncate_name(self.db_table, connection.ops.max_name_length())
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/db/__init__.py", line 33, in __getattr__
    return getattr(connections[DEFAULT_DB_ALIAS], item)
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/db/utils.py", line 202, in __getitem__
    backend = load_backend(db['ENGINE'])
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/db/utils.py", line 110, in load_backend
    return import_module('%s.base' % backend_name)
  File "/Users/apple/Documents/article/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/Users/apple/Documents/article/lib/python3.6/site-packages/django/db/backends/mysql/base.py", line 20, in <module>
    ) from err
django.core.exceptions.ImproperlyConfigured: Error loading MySQLdb module.
Did you install mysqlclient?

因为该虚拟环境之前都是可以正常使用的，很确定已经安装了mysqlclient等各种包，所以应该是Django中文件配置的问题，后来找到原因是需要在项目文件中的__init__.py中添加：

import pymysql
pymysql.install_as_MySQLdb()

就可以了