場景：按照github文檔上啟動一個flask的app，默認是用5000端口，如果5000端口被占用，啟動失敗。
樣例代碼：
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello():
return 'Hello, World!'
啟動的腳本：
$ env FLASK_APP=hello.py flask run
出錯信息如下：
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
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
問題：
那么該怎么指定新的端口呢？又如何查看5000端口指定的位置呢？
源碼分析，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/
可以看到在flask/app.py 以及cli.py中有指定。那么根據啟動命令flask run 實際上是啟動了一個http server，然后監聽了一個本地端口，等待連接。那么看看是否有相應的參數。
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這個參數，是指定端口的，默認是5000，那么嘗試修改一下。
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)
還一個5001的端口就成功了，由此可知，當出現一個我們不知道該如何解決問題的時候，我們可以嘗試著自己分析源碼，得到想要的結果。
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