如何实现Python Flask项目自动识别运行环境，部署时自动切换数据库连接方式

Great question! You don’t have to manually toggle that onServer variable—there are reliable, low-effort ways to auto-detect whether your app is running on PythonAnywhere or locally. Here are two straightforward approaches:

1. Check for PythonAnywhere-Specific Environment Variables #

PythonAnywhere sets unique environment variables for every running app. The most reliable one is PYTHONANYWHERE_USER, which holds your account username. We can use this to detect the server environment:

from flask import request, Flask, render_template, send_from_directory, url_for
from flask_sqlalchemy import SQLAlchemy
import sshtunnel
import os  # Add this import

sshtunnel.SSH_TIMEOUT = 5.0
sshtunnel.TUNNEL_TIMEOUT = 5.0

app = Flask(__name__)
app.jinja_env.filters['zip'] = zip
app.config['SEND_FILE_MAX_AGE_DEFAULT'] = 1

# Auto-detect if running on PythonAnywhere
on_server = 'PYTHONANYWHERE_USER' in os.environ

if on_server:
    app.config['SQLALCHEMY_DATABASE_URI']='mysql://username:password@username.mysql.pythonanywhere-services.com/username$default'
else:
    # SSH to pythonanywhere to get access to database
    tunnel = sshtunnel.SSHTunnelForwarder(
        ('ssh.pythonanywhere.com'),
        ssh_username='username',
        ssh_password='password',
        local_bind_address=("127.0.0.1",1000),
        remote_bind_address=('username.mysql.pythonanywhere-services.com', 3306)
    )
    # Start SSH tunneling
    tunnel.start()
    app.config['SQLALCHEMY_DATABASE_URI']='mysql://username:password@127.0.0.1:{}/username$default'.format(tunnel.local_bind_port)

db = SQLAlchemy(app)

2. Check the Server Hostname #

Another method is to inspect the hostname of the machine running your app. On PythonAnywhere, your server’s hostname will always include pythonanywhere.com:

from flask import request, Flask, render_template, send_from_directory, url_for
from flask_sqlalchemy import SQLAlchemy
import sshtunnel
import socket  # Add this import

sshtunnel.SSH_TIMEOUT = 5.0
sshtunnel.TUNNEL_TIMEOUT = 5.0

app = Flask(__name__)
app.jinja_env.filters['zip'] = zip
app.config['SEND_FILE_MAX_AGE_DEFAULT'] = 1

# Auto-detect using hostname
hostname = socket.gethostname()
on_server = 'pythonanywhere.com' in hostname

if on_server:
    app.config['SQLALCHEMY_DATABASE_URI']='mysql://username:password@username.mysql.pythonanywhere-services.com/username$default'
else:
    # SSH to pythonanywhere to get access to database
    tunnel = sshtunnel.SSHTunnelForwarder(
        ('ssh.pythonanywhere.com'),
        ssh_username='username',
        ssh_password='password',
        local_bind_address=("127.0.0.1",1000),
        remote_bind_address=('username.mysql.pythonanywhere-services.com', 3306)
    )
    # Start SSH tunneling
    tunnel.start()
    app.config['SQLALCHEMY_DATABASE_URI']='mysql://username:password@127.0.0.1:{}/username$default'.format(tunnel.local_bind_port)

db = SQLAlchemy(app)

Quick Security Note #

Hardcoding credentials (like your database and SSH passwords) directly in your code is a bad practice. For better security, store these values in environment variables:

• On PythonAnywhere, you can set them in your app’s "Web" settings under "Environment variables".
• Locally, use a .env file with the python-dotenv package to load them into os.environ.

内容的提问来源于stack exchange，提问作者aldo