python flask 如何修改默认端口号

场景：按照github文档上启动一个flask的app，默认是用5000端口，如果5000端口被占用，启动失败。

样例代码：

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
    return 'Hello, World!'

启动的脚本：

$ env FLASK_APP=hello.py flask run

出错信息如下：

renjg@renjg-HP-Compaq-Pro-6380-MT:~/WorkSpace/python/django$ env FLASK_APP=index.py flask run
 * Serving Flask app "index.py"
 * Environment: production
   WARNING: Do not use the development server in a production environment.
   Use a production WSGI server instead.
 * Debug mode: off
Traceback (most recent call last):
  File "/usr/local/bin/flask", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python2.7/dist-packages/flask/cli.py", line 894, in main
    cli.main(args=args, prog_name=name)
  File "/usr/local/lib/python2.7/dist-packages/flask/cli.py", line 557, in main
    return super(FlaskGroup, self).main(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/click/decorators.py", line 64, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/flask/cli.py", line 771, in run_command
    threaded=with_threads, ssl_context=cert)
  File "/usr/local/lib/python2.7/dist-packages/werkzeug/serving.py", line 814, in run_simple
    inner()
  File "/usr/local/lib/python2.7/dist-packages/werkzeug/serving.py", line 774, in inner
    fd=fd)
  File "/usr/local/lib/python2.7/dist-packages/werkzeug/serving.py", line 660, in make_server
    passthrough_errors, ssl_context, fd=fd)
  File "/usr/local/lib/python2.7/dist-packages/werkzeug/serving.py", line 577, in __init__
    self.address_family), handler)
  File "/usr/lib/python2.7/SocketServer.py", line 417, in __init__
    self.server_bind()
  File "/usr/lib/python2.7/BaseHTTPServer.py", line 108, in server_bind
    SocketServer.TCPServer.server_bind(self)
  File "/usr/lib/python2.7/SocketServer.py", line 431, in server_bind
    self.socket.bind(self.server_address)
  File "/usr/lib/python2.7/socket.py", line 228, in meth
    return getattr(self._sock,name)(*args)
socket.error: [Errno 98] Address already in use

问题：

那么该怎么指定新的端口呢？又如何查看5000端口指定的位置呢？

源码分析，首先clone github上的flask框架，然后直接grep命令查看5000的位置。

renjg@renjg-HP-Compaq-Pro-6380-MT:~/WorkSpace/python/django/flask$ grep 5000 * -nrw
docs/patterns/appdispatch.rst:28:    run_simple('localhost', 5000, application, use_reloader=True)
docs/patterns/appdispatch.rst:48:        run_simple('localhost', 5000, app,
docs/config.rst:417:     * Running on http://127.0.0.1:5000/
docs/config.rst:453:     * Running on http://127.0.0.1:5000/
docs/quickstart.rst:51:     * Running on http://127.0.0.1:5000/
docs/quickstart.rst:66:     * Running on http://127.0.0.1:5000/
docs/quickstart.rst:72:Now head over to `http://127.0.0.1:5000/ <http://127.0.0.1:5000/>`_, and you
docs/deploying/wsgi-standalone.rst:38:    $ uwsgi --http 127.0.0.1:5000 --module myproject:app
docs/deploying/wsgi-standalone.rst:55:    http_server = WSGIServer(('', 5000), app)
docs/server.rst:26:*http://localhost:5000/*.
docs/cli.rst:97:     * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
docs/cli.rst:143:     * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
docs/tutorial/static.rst:58:Go to http://127.0.0.1:5000/auth/login and the page should look like the
docs/tutorial/factory.rst:169:     * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
docs/tutorial/factory.rst:174:Visit http://127.0.0.1:5000/hello in a browser and you should see the
docs/tutorial/templates.rst:174:then go to http://127.0.0.1:5000/auth/register.
examples/javascript/README.rst:39:Open http://127.0.0.1:5000 in a browser.
examples/tutorial/README.rst:62:Open http://127.0.0.1:5000 in a browser.
flask/app.py:878:        :param port: the port of the webserver. Defaults to ``5000`` or the
flask/app.py:925:        _port = 5000
flask/cli.py:738:@click.option('--port', '-p', default=5000,
README.rst:43:     * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
tests/test_basic.py:369:        SERVER_NAME='localhost:5000',
tests/test_basic.py:377:    rv = client.get('/', 'http://localhost:5000/')
tests/test_basic.py:385:        SERVER_NAME='127.0.0.1:5000',
tests/test_basic.py:393:    rv = client.get('/', 'http://127.0.0.1:5000/')
tests/test_basic.py:1448:        SERVER_NAME='localhost.localdomain:5000'
tests/test_basic.py:1463:    rv = client.get('/', 'http://localhost.localdomain:5000')
tests/test_basic.py:1466:    rv = client.get('/', 'https://localhost.localdomain:5000')
tests/test_reqctx.py:72:        SERVER_NAME='localhost.localdomain:5000'
tests/test_reqctx.py:85:               'http://localhost.localdomain:5000/'
tests/test_reqctx.py:89:               'http://foo.localhost.localdomain:5000/'
tests/test_reqctx.py:97:            "('localhost.localdomain:5000') does not match the "

　可以看到在flask/app.py 以及cli.py中有指定。那么根据启动命令flask run 实际上是启动了一个http server，然后监听了一个本地端口，等待连接。那么看看是否有相应的参数。

renjg@renjg-HP-Compaq-Pro-6380-MT:~/WorkSpace/python/django/flask$ flask --help
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/flask/cli.py", line 529, in list_commands
    rv.update(info.load_app().cli.list_commands(ctx))
  File "/usr/local/lib/python2.7/dist-packages/flask/cli.py", line 384, in load_app
    'Could not locate a Flask application. You did not provide '
NoAppException: Could not locate a Flask application. You did not provide the "FLASK_APP" environment variable, and a "wsgi.py" or "app.py" module was not found in the current directory.
Usage: flask [OPTIONS] COMMAND [ARGS]...

  A general utility script for Flask applications.

  Provides commands from Flask, extensions, and the application. Loads the
  application defined in the FLASK_APP environment variable, or from a
  wsgi.py file. Setting the FLASK_ENV environment variable to 'development'
  will enable debug mode.

    $ export FLASK_APP=hello.py
    $ export FLASK_ENV=development
    $ flask run

Options:
  --version  Show the flask version
  --help     Show this message and exit.

Commands:
  routes  Show the routes for the app.
  run     Runs a development server.
  shell   Runs a shell in the app context.
renjg@renjg-HP-Compaq-Pro-6380-MT:~/WorkSpace/python/django/flask$ flask run --help
Usage: flask run [OPTIONS]

  Run a local development server.

  This server is for development purposes only. It does not provide the
  stability, security, or performance of production WSGI servers.

  The reloader and debugger are enabled by default if FLASK_ENV=development
  or FLASK_DEBUG=1.

Options:
  -h, --host TEXT                 The interface to bind to.
  -p, --port INTEGER              The port to bind to.
  --cert PATH                     Specify a certificate file to use HTTPS.
  --key FILE                      The key file to use when specifying a
                                  certificate.
  --reload / --no-reload          Enable or disable the reloader. By default
                                  the reloader is active if debug is enabled.
  --debugger / --no-debugger      Enable or disable the debugger. By default
                                  the debugger is active if debug is enabled.
  --eager-loading / --lazy-loader
                                  Enable or disable eager loading. By default
                                  eager loading is enabled if the reloader is
                                  disabled.
  --with-threads / --without-threads
                                  Enable or disable multithreading.
  --help                          Show this message and exit.

　可以看到有-p这个参数，是指定端口的，默认是5000，那么尝试修改一下。

renjg@renjg-HP-Compaq-Pro-6380-MT:~/WorkSpace/python/django$ env FLASK_APP=index.py flask run -p 5001
 * Serving Flask app "index.py"
 * Environment: production
   WARNING: Do not use the development server in a production environment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5001/ (Press CTRL+C to quit)

　还一个5001的端口就成功了，由此可知，当出现一个我们不知道该如何解决问题的时候，我们可以尝试着自己分析源码，得到想要的结果。