pythonflask如何修改默认端⼝号的⽅法步骤场景：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__)
@ute('/')
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>
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_ctxmand.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)
<: [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 127.0.0.1:5000/
docs/config.rst:453:  * Running on 127.0.0.1:5000/
docs/quickstart.rst:51:  * Running on 127.0.0.1:5000/
docs/quickstart.rst:66:  * Running on 127.0.0.1:5000/
docs/quickstart.rst:72:Now head over to `127.0.0.1:5000/ <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:*localhost:5000/*.
reactor debug mode is enableddocs/cli.rst:97:  * Running on 127.0.0.1:5000/ (Press CTRL+C to quit)
docs/cli.rst:143:  * Running on 127.0.0.1:5000/ (Press CTRL+C to quit)
docs/tutorial/static.rst:58:Go to 127.0.0.1:5000/auth/login and the page should look like the
docs/tutorial/factory.rst:169:  * Running on 127.0.0.1:5000/ (Press CTRL+C to quit)
docs/tutorial/factory.rst:174:Visit 127.0.0.1:5000/hello in a browser and you should see the
docs/tutorial/templates.rst:174:then go to 127.0.0.1:5000/auth/register.
examples/javascript/README.rst:39:Open 127.0.0.1:5000 in a browser.
examples/tutorial/README.rst:62:Open 127.0.0.1:5000 in a browser.
<strong>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,</strong>
README.rst:43:  * Running on 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 = ('/', 'localhost:5000/')
tests/test_basic.py:385:    SERVER_NAME='127.0.0.1:5000',
tests/test_basic.py:393:  rv = ('/', '127.0.0.1:5000/')
tests/test_basic.py:1448:    SERVER_NAME='localhost.localdomain:5000'
tests/test_basic.py:1463:  rv = ('/', 'localhost.localdomain:5000')
tests/test_basic.py:1466:  rv = ('/', 'localhost.localdomain:5000')
tests/test_reqctx.py:72:    SERVER_NAME='localhost.localdomain:5000'
tests/test_reqctx.py:85:        'localhost.localdomain:5000/'
tests/test_reqctx.py:89:        '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.
<strong> -p, --port INTEGER      The port to bind to.</strong>
--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 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。
以上就是本⽂的全部内容，希望对⼤家的学习有所帮助，也希望⼤家多多⽀持。

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