Docker容器内启动Django报错TypeError: NoneType不可迭代

使用VSCode Remote - Container扩展在Docker中搭建Python 3 & PostgreSQL开发容器，相关配置文件如下：

devcontainer.json #

// 配置遵循devcontainer官方规范，可通过docker-compose.yml中的VARIANT参数指定Python版本
{
  "name": "Python 3 & PostgreSQL",
  "dockerComposeFile": "docker-compose.yml",
  "service": "app",
  "workspaceFolder": "/workspace",

  // 工具专属配置
  "customizations": {
      // VS Code专属配置
      "vscode": {
          // 容器创建时写入的默认settings.json配置
          "settings": { 
              "python.defaultInterpreterPath": "/usr/local/bin/python",
              "python.linting.enabled": true,
              "python.linting.pylintEnabled": true,
              "python.formatting.autopep8Path": "/usr/local/py-utils/bin/autopep8",
              "python.formatting.blackPath": "/usr/local/py-utils/bin/black",
              "python.formatting.yapfPath": "/usr/local/py-utils/bin/yapf",
              "python.linting.banditPath": "/usr/local/py-utils/bin/bandit",
              "python.linting.flake8Path": "/usr/local/py-utils/bin/flake8",
              "python.linting.mypyPath": "/usr/local/py-utils/bin/mypy",
              "python.linting.pycodestylePath": "/usr/local/py-utils/bin/pycodestyle",
              "python.linting.pydocstylePath": "/usr/local/py-utils/bin/pydocstyle",
              "python.linting.pylintPath": "/usr/local/py-utils/bin/pylint",
              "python.testing.pytestPath": "/usr/local/py-utils/bin/pytest"
          },
          
          // 容器创建时自动安装的扩展ID列表
          "extensions": [
              "ms-python.python",
              "ms-python.vscode-pylance"
          ]
      }
  },

  // 配置需要本地转发的容器端口，可用于容器间、容器与主机的网络通信
  "forwardPorts": [5000, 5432, 8000],

  // 容器创建完成后自动执行的命令
  "postCreateCommand": "pip install --user poetry"

  // 注释掉以下配置则默认使用root用户连接容器
  // "remoteUser": "vscode"
}

docker-compose.yml #

version: '3.8'

services:   
  app:
    build:
      context: ..
      dockerfile: .devcontainer/Dockerfile
      args:
        # 可选Python版本：3, 3.10, 3.9, 3.8, 3.7, 3.6
        # 可追加-bullseye或-buster指定操作系统版本，本地arm64/Apple Silicon设备建议使用-bullseye变体
        VARIANT: 3.9-bullseye
        # 可选Node.js版本
        NODE_VERSION: "lts/*"

    volumes:
      - ..:/workspace:cached

    # 覆盖默认启动命令，保证容器启动后不会自动退出
    command: sleep infinity

    # 与数据库容器共享网络栈，支持devcontainer.json中的端口转发配置
    network_mode: service:db
    # 取消下一行注释则使用非root用户运行所有进程
    # user: vscode

    # 注意：应用端口请在devcontainer.json的forwardPorts中配置，直接在本文件配置ports字段无法在Codespace环境生效

  db:
    image: postgres:latest
    restart: unless-stopped
    volumes:
      - postgres-data:/var/lib/postgresql/data
    environment:
      POSTGRES_USER: postgres
      POSTGRES_DB: postgres
      POSTGRES_PASSWORD: postgres
    # 注意：PostgreSQL端口请在devcontainer.json的forwardPorts中配置，直接在本文件配置ports字段无法在Codespace环境生效

volumes:   
  postgres-data: null

Dockerfile #

# [可选] Python版本（本地arm64/Apple Silicon设备请使用-bullseye变体）：3, 3.10, 3.9, 3.8, 3.7, 3.6, 3-bullseye, 3.10-bullseye,
# 3.9-bullseye, 3.8-bullseye, 3.7-bullseye, 3.6-bullseye, 3-buster, 3.10-buster, 3.9-buster, 3.8-buster, 3.7-buster, 3.6-buster 
ARG VARIANT=3-bullseye 
FROM mcr.microsoft.com/vscode/devcontainers/python:0-${VARIANT}

ENV PYTHONUNBUFFERED 1

# [可选] Node.js版本：none, lts/*, 16, 14, 12, 10 
ARG NODE_VERSION="none" 
RUN if [ "${NODE_VERSION}" != "none" ]; then su vscode -c "umask 0002 && . /usr/local/share/nvm/nvm.sh && nvm install ${NODE_VERSION} 2>&1"; fi

# [可选] 如果依赖变动频率低，可取消以下注释将依赖直接打入镜像
# COPY requirements.txt /tmp/pip-tmp/
# RUN pip3 --disable-pip-version-check --no-cache-dir install -r /tmp/pip-tmp/requirements.txt \
#    && rm -rf /tmp/pip-tmp

# [可选] 取消以下注释安装额外的系统依赖包
# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive
#     && apt-get -y install --no-install-recommends <your-package-list-here>

环境搭建完成后，手动安装Poetry管理项目依赖，通过pip3 install和poetry install完成依赖安装后，执行python3 manage.py runserver或poetry run python3 manage.py runserver启动Django服务时抛出如下异常：

Exception in thread django-main-thread:
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/threading.py", line 973, in _bootstrap_inner
    self.run()
  File "/usr/local/lib/python3.9/threading.py", line 910, in run
    self._target(*self._args, **self._kwargs)
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/utils/autoreload.py", line 64, in wrapper
    fn(*args, **kwargs)
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/core/management/commands/runserver.py", line 118, in inner_run
    self.check(display_num_errors=True)
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/core/management/base.py", line 419, in check
    all_issues = checks.run_checks(
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/core/checks/registry.py", line 76, in run_checks
    new_errors = check(app_configs=app_configs, databases=databases)
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/core/checks/urls.py", line 13, in check_url_config
    return check_resolver(resolver)
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/core/checks/urls.py", line 23, in check_resolver
    return check_method()
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/urls/resolvers.py", line 417, in check
    messages.extend(check_resolver(pattern))
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/core/checks/urls.py", line 23, in check_resolver
    return check_method()
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/urls/resolvers.py", line 419, in check
    return messages or self.pattern.check()
  File "/root/.cache/pypoetry/virtualenvs/backend-xS3fZVNL-py3.9/lib/python3.9/site-packages/django/urls/resolvers.py", line 282, in check
    if '(?P<' in route or route.startswith('^') or route.endswith('$'):
TypeError: argument of type 'NoneType' is not iterable

Docker实例运行在2020款MacBook Air设备上。

该报错与Docker运行环境、Mac硬件架构、Poetry依赖管理逻辑均无关，本质是Django项目自身URL配置错误：
Django启动阶段会自动校验所有注册的路由规则，校验到某条路由的路径字段（route）值为None，执行字符串成员判断'(?P<' in route时，None类型不支持迭代判断，直接抛出类型错误。
常见触发场景包括：

• 编写path/re_path路由规则时漏填第一个路由字符串参数，直接传入视图函数
• 动态生成路由的逻辑存在bug，最终传入路由方法的路径值为None
• 根路由通过include()引入子路由模块时导入路径错误，导致子路由对象属性为空

按以下步骤排查修复即可，无需调整容器配置、重装依赖：

• 全局检索项目内所有urls.py文件，逐行核对path()、re_path()、url()方法的传参：确认第一个参数为字符串格式的路由规则，不可省略、不可传None。典型错误写法为path(views.HomeView.as_view(), name='home')，漏写了空路径的第一个参数''，修正为path('', views.HomeView.as_view(), name='home')即可
• 若存在动态生成路由的逻辑，逐段打印路由变量值，排查返回None的分支
• 检查根路由文件中include()引入的子路由路径，确认模块导入正常，不存在导入失败导致子路由属性为空的问题

修复完成后重新执行启动命令即可正常运行Django服务。

内容的提问来源于stack exchange，提问作者CatalyticMusa