Heroku部署Flask应用报错：无法从flask_session导入Session

问题回顾 #

将本地运行正常的Flask网站部署到Heroku时，先遇到ImportError: cannot import name 'Session' from 'flask_session'错误，应用启动失败并触发H10崩溃错误，日志详情：

2023-07-24T02:31:34.494523+00:00 app[web.1]: ImportError: cannot import name 'Session' from 'flask_session' (unknown location)
2023-07-24T02:31:34.494654+00:00 app[web.1]: [2023-07-24 02:31:34 +0000] [8] [INFO] Worker exiting (pid: 8)
2023-07-24T02:31:34.526827+00:00 app[web.1]: [2023-07-24 02:31:34 +0000] [2] [ERROR] Worker (pid:7) exited with code 3
2023-07-24T02:31:34.528740+00:00 app[web.1]: [2023-07-24 02:31:34 +0000] [2] [ERROR] Worker (pid:8) was sent SIGTERM!
2023-07-24T02:31:34.627270+00:00 app[web.1]: [2023-07-24 02:31:34 +0000] [2] [ERROR] Shutting down: Master
2023-07-24T02:31:34.627284+00:00 app[web.1]: [2023-07-24 02:31:34 +0000] [2] [ERROR] Reason: Worker failed to boot.
2023-07-24T02:31:35.098046+00:00 heroku[web.1]: Process exited with status 3
2023-07-24T02:31:35.130639+00:00 heroku[web.1]: State changed from starting to crashed
2023-07-24T02:31:48.794602+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=flasker888-950c07d40a01.herokuapp.com request_id=7d5cb524-3382-4408-b53d-992e3382cb82 fwd="114.181.123.229" dyno= connect= service= status=503 bytes= protocol=https
2023-07-24T02:31:48.979619+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=flasker888-950c07d40a01.herokuapp.com request_id=a74969fb-4dbf-44e0-be3d-a21dd1c2d064 fwd="114.181.123.229" dyno= connect= service= status=503 bytes= protocol=https

通过pip freeze生成完整的requirements.txt解决了flask_session的问题，但现在Heroku无法识别flask-bcrypt。当前requirements.txt内容：

blinker==1.6.2
cachelib==0.10.2
click==8.1.3
colorama==0.4.6
Flask==2.3.2
Flask-Login==0.6.2
Flask-Session==0.5.0
Flask-SQLAlchemy==3.0.5
greenlet==2.0.2
gunicorn==21.1.0
itsdangerous==2.1.2
Jinja2==3.1.2
MarkupSafe==2.1.3
numpy==1.25.1
packaging==23.1
pandas==2.0.3
psycopg2==2.9.6
python-dateutil==2.8.2
pytz==2023.3
six==1.16.0
SQLAlchemy==2.0.17
typing_extensions==4.7.1
tzdata==2023.3
Werkzeug==2.3.6

解决步骤 #

• 确保本地虚拟环境已安装flask-bcrypt：激活虚拟环境后，执行pip install flask-bcrypt。如果本地没安装这个包，pip freeze不会把它加入requirements.txt，这是Heroku识别不了的核心原因。
• 重新生成requirements.txt：执行pip freeze > requirements.txt，此时检查文件内容，应该会出现Flask-Bcrypt==x.x.x的条目（x.x.x为实际安装的版本）。
• 提交更新到Heroku：依次执行以下命令

  git add requirements.txt
  git commit -m "添加flask-bcrypt依赖"
  git push heroku main
  

• 若仍有问题，检查版本兼容性：当前使用的Flask版本是2.3.2，可指定兼容的flask-bcrypt版本，比如在requirements.txt中手动添加Flask-Bcrypt==1.0.1（该版本适配Flask 2.x系列），再重新提交。

内容的提问来源于stack exchange，提问作者Dragynjump