mysqlclient MacOS 使用报错 NameError: name ‘_mysql’ is not defined

背景

最近使用 django 作为一个服务的后台，在使用 mysqlclient 链接 mysql 数据库时发生一个奇怪的报错 NameError: name ‘_mysql’ is not defined

下面是具体报错信息

INFO] 2021-04-07 02:27:57,613 Watching for file changes with StatReloader
Exception in thread django-main-thread:
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/__init__.py", line 18, in <module>
    from . import _mysql
ImportError: dlopen(/usr/local/lib/python3.7/site-packages/MySQLdb/_mysql.cpython-37m-darwin.so, 2): Library not loaded: @rpath/libmysqlclient.21.dylib
  Referenced from: /usr/local/lib/python3.7/site-packages/MySQLdb/_mysql.cpython-37m-darwin.so
  Reason: image not found

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 926, in _bootstrap_inner
    self.run()
  File "/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.7/site-packages/django/utils/autoreload.py", line 53, in wrapper
    fn(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/commands/runserver.py", line 110, in inner_run
    autoreload.raise_last_exception()
  File "/usr/local/lib/python3.7/site-packages/django/utils/autoreload.py", line 76, in raise_last_exception
    raise _exception[1]
  File "/usr/local/lib/python3.7/site-packages/django/core/management/__init__.py", line 357, in execute
    autoreload.check_errors(django.setup)()
  File "/usr/local/lib/python3.7/site-packages/django/utils/autoreload.py", line 53, in wrapper
    fn(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/django/__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/usr/local/lib/python3.7/site-packages/django/apps/registry.py", line 114, in populate
    app_config.import_models()
  File "/usr/local/lib/python3.7/site-packages/django/apps/config.py", line 211, in import_models
    self.models_module = import_module(models_module_name)
  File "/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/usr/local/lib/python3.7/site-packages/django/contrib/auth/models.py", line 2, in <module>
    from django.contrib.auth.base_user import AbstractBaseUser, BaseUserManager
  File "/usr/local/lib/python3.7/site-packages/django/contrib/auth/base_user.py", line 48, in <module>
    class AbstractBaseUser(models.Model):
  File "/usr/local/lib/python3.7/site-packages/django/db/models/base.py", line 122, in __new__
    new_class.add_to_class('_meta', Options(meta, app_label))
  File "/usr/local/lib/python3.7/site-packages/django/db/models/base.py", line 326, in add_to_class
    value.contribute_to_class(cls, name)
  File "/usr/local/lib/python3.7/site-packages/django/db/models/options.py", line 206, in contribute_to_class
    self.db_table = truncate_name(self.db_table, connection.ops.max_name_length())
  File "/usr/local/lib/python3.7/site-packages/django/db/__init__.py", line 28, in __getattr__
    return getattr(connections[DEFAULT_DB_ALIAS], item)
  File "/usr/local/lib/python3.7/site-packages/django/db/utils.py", line 214, in __getitem__
    backend = load_backend(db['ENGINE'])
  File "/usr/local/lib/python3.7/site-packages/django/db/utils.py", line 111, in load_backend
    return import_module('%s.base' % backend_name)
  File "/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/usr/local/lib/python3.7/site-packages/django/db/backends/mysql/base.py", line 15, in <module>
    import MySQLdb as Database
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/__init__.py", line 24, in <module>
    version_info, _mysql.version_info, _mysql.__file__
NameError: name '_mysql' is not defined

其中最关键的报错信息：Library not loaded: @rpath/libmysqlclient.21.dylib ，没有加载 libmysqlclient.21.dylib 这个库，通过 find 命令本机查找 libmysqlclient.21.dylib 位置（每个人电脑上 mysql 安装路径不同，根据具体情况具体分析）。
find / -name libmysqlclient.21.dylib

解决方案

只需要将找到的 libmysqlclient.21.dylib 路径添加到 LD_LIBRARY_PATH （动态库查找路径）即可，添加环境变量

export LD_LIBRARY_PATH=/usr/local/mysql-8.0.18-macos10.14-x86_64/lib

运行服务即可

python manage.py runserver

参考