运行manage.py runserver时出现django-main-thread错误

尝试将Django应用部署到Digital Ocean后修改了代码，本地运行python3 manage.py runserver时出现以下错误：

(my_chaburah) ~/Desktop/Code/my_chaburah (main)
$ python3 manage.py runserver
Watching for file changes with StatReloader
Exception in thread django-main-thread:
Traceback (most recent call last):
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/db/backends/postgresql/base.py", line 24, in <module>
    import psycopg2 as Database
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/psycopg2/__init__.py", line 51, in <module>
    from psycopg2._psycopg import (                     # noqa
ImportError: dlopen(/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/psycopg2/_psycopg.cpython-39-darwin.so, 0x0002): Library not loaded: '/opt/homebrew/opt/postgresql/lib/libpq.5.dylib'
  Referenced from: '/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/psycopg2/_psycopg.cpython-39-darwin.so'
  Reason: tried: '/opt/homebrew/opt/postgresql/lib/libpq.5.dylib' (no such file), '/usr/local/lib/libpq.5.dylib' (no such file), '/usr/lib/libpq.5.dylib' (no such file), '/opt/homebrew/Cellar/postgresql@14/14.5_5/lib/libpq.5.dylib' (no such file), '/usr/local/lib/libpq.5.dylib' (no such file), '/usr/lib/libpq.5.dylib' (no such file)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/homebrew/Cellar/python@3.9/3.9.15/Frameworks/Python.framework/Versions/3.9/lib/python3.9/threading.py", line 980, in _bootstrap_inner
    self.run()
  File "/opt/homebrew/Cellar/python@3.9/3.9.15/Frameworks/Python.framework/Versions/3.9/lib/python3.9/threading.py", line 917, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/utils/autoreload.py", line 64, in wrapper
    fn(*args, **kwargs)
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/core/management/commands/runserver.py", line 125, in inner_run
    autoreload.raise_last_exception()
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/utils/autoreload.py", line 87, in raise_last_exception
    raise _exception[1]
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/core/management/__init__.py", line 398, in execute
    autoreload.check_errors(django.setup)()
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/utils/autoreload.py", line 64, in wrapper
    fn(*args, **kwargs)
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/apps/registry.py", line 116, in populate
    app_config.import_models()
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/apps/config.py", line 304, in import_models
    self.models_module = import_module(models_module_name)
  File "/opt/homebrew/Cellar/python@3.9/3.9.15/Frameworks/Python.framework/Versions/3.9/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 850, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/contrib/auth/models.py", line 3, in <module>
    from django.contrib.auth.base_user import AbstractBaseUser, BaseUserManager
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/contrib/auth/base_user.py", line 49, in <module>
    class AbstractBaseUser(models.Model):
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/db/models/base.py", line 141, in __new__
    new_class.add_to_class("_meta", Options(meta, app_label))
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/db/models/base.py", line 369, in add_to_class
    value.contribute_to_class(cls, name)
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/db/models/options.py", line 235, in contribute_to_class
    self.db_table, connection.ops.max_name_length()
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/utils/connection.py", line 15, in __getattr__
    return getattr(self._connections[self._alias], item)
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/utils/connection.py", line 62, in __getitem__
    conn = self.create_connection(alias)
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/db/utils.py", line 208, in create_connection
    backend = load_backend(db["ENGINE"])
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/db/utils.py", line 113, in load_backend
    return import_module("%s.base" % backend_name)
  File "/opt/homebrew/Cellar/python@3.9/3.9.15/Frameworks/Python.framework/Versions/3.9/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/django/db/backends/postgresql/base.py", line 28, in <module>
    raise ImproperlyConfigured("Error loading psycopg2 module: %s" % e)
django.core.exceptions.ImproperlyConfigured: Error loading psycopg2 module: dlopen(/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/psycopg2/_psycopg.cpython-39-darwin.so, 0x0002): Library not loaded: '/opt/homebrew/opt/postgresql/lib/libpq.5.dylib'
  Referenced from: '/Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/lib/python3.9/site-packages/psycopg2/_psycopg.cpython-39-darwin.so'
  Reason: tried: '/opt/homebrew/opt/postgresql/lib/libpq.5.dylib' (no such file), '/usr/local/lib/libpq.5.dylib' (no such file), '/usr/lib/libpq.5.dylib' (no such file), '/opt/homebrew/Cellar/postgresql@14/14.5_5/lib/libpq.5.dylib' (no such file), '/usr/local/lib/libpq.5.dylib' (no such file), '/usr/lib/libpq.5.dylib' (no such file)

当前目标是恢复本地应用正常运行，怀疑问题和虚拟环境、pip安装有关，也担心误删了文件。

这个错误是因为psycopg2找不到PostgreSQL的libpq依赖库，以下是几种修复方法：

方法1：重新安装PostgreSQL并建立软链接 #

• 先通过Homebrew重新安装PostgreSQL：

  brew reinstall postgresql
  

• 找到当前PostgreSQL的libpq路径，比如如果安装的是postgresql@14，路径可能是/opt/homebrew/Cellar/postgresql@14/<版本号>/lib/，然后建立软链接到错误提示的路径：

  ln -s /opt/homebrew/Cellar/postgresql@14/<你的版本号>/lib/libpq.5.dylib /opt/homebrew/opt/postgresql/lib/libpq.5.dylib
  

  注意替换<你的版本号>为实际安装的版本，比如14.10_1。

方法2：重新安装psycopg2-binary #

psycopg2-binary是预编译版本，自带依赖，不需要本地PostgreSQL库：

• 激活虚拟环境：

  source /Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/bin/activate
  

• 卸载原有的psycopg2：

  pip uninstall psycopg2
  

• 安装psycopg2-binary：

  pip install psycopg2-binary
  

方法3：重置虚拟环境 #

如果以上方法无效，直接重置虚拟环境：

• 退出虚拟环境：

  deactivate
  

• 删除现有虚拟环境：

  rm -rf /Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC
  

• 重新创建虚拟环境：

  python3 -m venv /Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC
  

• 激活虚拟环境并重新安装所有依赖：

  source /Users/almoni/.local/share/virtualenvs/my_chaburah-AiCSV-sC/bin/activate
  pip install -r requirements.txt
  

方法4：临时切换到SQLite（仅用于本地测试） #

如果只是想快速恢复本地运行，不需要连接PostgreSQL，可以临时修改settings.py里的数据库配置为SQLite：

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': BASE_DIR / 'db.sqlite3',
    }
}

修改后重新运行python3 manage.py runserver即可，后续部署时再改回PostgreSQL配置。

内容的提问来源于stack exchange，提问作者Yehuda