如何使用烧瓶框架在 python 中编写 switch 语句？答案

【问题标题】：How can i write a switch statement in python using flask framework?如何使用烧瓶框架在 python 中编写 switch 语句？
【发布时间】：2020-05-19 05:49:17
【问题描述】：

这里是代码

switcher = {
    "1": func1(),
    "2": func2(),
    "3": func3(),
    "4": func4(),
    "5": func5(),
    "6": func6(),
    "9": func7(),
    "11": func8(),
    "12":func9(),
    "13": func10()
}

@app.route('/ussdcallback', methods=['GET', 'POST'])
def switch(text = request.values.get("text", None)):
    session_id = request.values.get("sessionId", None)
    service_code = request.values.get("serviceCode", None)
    func = switcher.get(text, "none")
    return func()

这是我得到的输出

Traceback (most recent call last):
2020-05-19T05:44:17.416279+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/arbiter.py", line 583, in spawn_worker
2020-05-19T05:44:17.416279+00:00 app[web.1]:     worker.init_process()
2020-05-19T05:44:17.416280+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/workers/base.py", line 119, in init_process
2020-05-19T05:44:17.416280+00:00 app[web.1]:     self.load_wsgi()
2020-05-19T05:44:17.416280+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/workers/base.py", line 144, in load_wsgi
2020-05-19T05:44:17.416280+00:00 app[web.1]:     self.wsgi = self.app.wsgi()
2020-05-19T05:44:17.416281+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/base.py", line 67, in wsgi
2020-05-19T05:44:17.416281+00:00 app[web.1]:     self.callable = self.load()
2020-05-19T05:44:17.416281+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/wsgiapp.py", line 49, in load
2020-05-19T05:44:17.416281+00:00 app[web.1]:     return self.load_wsgiapp()
2020-05-19T05:44:17.416282+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/wsgiapp.py", line 39, in load_wsgiapp
2020-05-19T05:44:17.416282+00:00 app[web.1]:     return util.import_app(self.app_uri)
2020-05-19T05:44:17.416282+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/util.py", line 358, in import_app
2020-05-19T05:44:17.416282+00:00 app[web.1]:     mod = importlib.import_module(module)
2020-05-19T05:44:17.416283+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/importlib/__init__.py", line 126, in import_module
2020-05-19T05:44:17.416284+00:00 app[web.1]:     return _bootstrap._gcd_import(name[level:], package, level)
2020-05-19T05:44:17.416285+00:00 app[web.1]:   File "<frozen importlib._bootstrap>", line 994, in _gcd_import
2020-05-19T05:44:17.416285+00:00 app[web.1]:   File "<frozen importlib._bootstrap>", line 971, in _find_and_load
2020-05-19T05:44:17.416285+00:00 app[web.1]:   File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
2020-05-19T05:44:17.416285+00:00 app[web.1]:   File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
2020-05-19T05:44:17.416286+00:00 app[web.1]:   File "<frozen importlib._bootstrap_external>", line 678, in exec_module
2020-05-19T05:44:17.416286+00:00 app[web.1]:   File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
2020-05-19T05:44:17.416286+00:00 app[web.1]:   File "/app/run.py", line 1, in <module>
2020-05-19T05:44:17.416286+00:00 app[web.1]:     from app import app
2020-05-19T05:44:17.416286+00:00 app[web.1]:   File "/app/app/__init__.py", line 359, in <module>
2020-05-19T05:44:17.416287+00:00 app[web.1]:     from app import routes, usrmgt, safeDeposit
2020-05-19T05:44:17.416287+00:00 app[web.1]:   File "/app/app/routes.py", line 22, in <module>
2020-05-19T05:44:17.416287+00:00 app[web.1]:     "1": radar(),
2020-05-19T05:44:17.416287+00:00 app[web.1]:   File "/app/app/radar.py", line 161, in radar
2020-05-19T05:44:17.416287+00:00 app[web.1]:     resp = make_response(response, 200)
2020-05-19T05:44:17.416288+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/flask/helpers.py", line 223, in make_response
2020-05-19T05:44:17.416288+00:00 app[web.1]:     return current_app.make_response(args)
2020-05-19T05:44:17.416288+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/werkzeug/local.py", line 347, in __getattr__
2020-05-19T05:44:17.416288+00:00 app[web.1]:     return getattr(self._get_current_object(), name)
2020-05-19T05:44:17.416288+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/werkzeug/local.py", line 306, in _get_current_object
2020-05-19T05:44:17.416289+00:00 app[web.1]:     return self.__local()
2020-05-19T05:44:17.416289+00:00 app[web.1]:   File "/app/.heroku/python/lib/python3.6/site-packages/flask/globals.py", line 52, in _find_app
2020-05-19T05:44:17.416311+00:00 app[web.1]:     raise RuntimeError(_app_ctx_err_msg)
2020-05-19T05:44:17.416312+00:00 app[web.1]: RuntimeError: Working outside of application context.
2020-05-19T05:44:17.416312+00:00 app[web.1]: 
2020-05-19T05:44:17.416313+00:00 app[web.1]: This typically means that you attempted to use functionality that needed
2020-05-19T05:44:17.416313+00:00 app[web.1]: to interface with the current application object in some way. To solve
2020-05-19T05:44:17.416313+00:00 app[web.1]: this, set up an application context with app.app_context().  See the
2020-05-19T05:44:17.416319+00:00 app[web.1]: documentation for more information.
2020-05-19T05:44:17.416716+00:00 app[web.1]: [2020-05-19 05:44:17 +0000] [11] [INFO] Worker exiting (pid: 11)
2020-05-19T05:44:18.050667+00:00 app[web.1]: [2020-05-19 05:44:18 +0000] [4] [INFO] Shutting down: Master
2020-05-19T05:44:18.050834+00:00 app[web.1]: [2020-05-19 05:44:18 +0000] [4] [INFO] Reason: Worker failed to boot.
2020-05-19T05:44:18.145123+00:00 heroku[web.1]: Process exited with status 3
2020-05-19T05:44:18.190532+00:00 heroku[web.1]: State changed from up to crashed

【问题讨论】：

请解释你要做什么！并向我们展示引发异常的代码。您的代码不适合。
我正在尝试在 python 中使用替代 switch 语句来使用烧瓶框架调用各种函数。而不是常规的 IF ... ELSE 语句。
总结一下如何使用flask在python中实现switch语句在web上运行
Python 没有 switch 语句。您正在尝试使用带有函数的 dict。当您将值放入时，您正在调用函数，您需要将实际的函数对象放入其中，所以不要调用它们。然后当你从字典中检索函数时，你调用它。
请问我可以举个例子吗？

标签： python flask python-3.7

【解决方案1】：

我相信您的问题在于您实际上是在 switcher dict 中调用函数并留下调用结果，而不是对函数的引用。如果您从 switcher 字典中的函数中删除括号，则可以获取对函数本身的引用，然后像您一样使用 func() 调用它们。

switcher = {
    "1": func1,  # No ()
    ...
}

简单的例子：

>>> def x(): print("test")
...
>>> def y(): print("another test")
...
>>> z = {1:x, 2:y}
>>> z[1]()
test
>>> z[2]()
another test

【讨论】：

【解决方案2】：

TL;DR - 在 Flask 处理请求之前，您正在使用 request "thread"-local，从而导致此错误。您不想使用线程局部值来定义函数参数输入。

您在这里遇到的问题是，您希望函数参数的默认值在函数的调用时间而不是在其定义时间进行评估：

def when_is_this_called(): print("NOW!")

def some_func(an_arg=when_is_this_called()):
    pass

print("Functions defined")
some_func()

将打印：

NOW!
Functions defined

代替：

Functions defined
NOW!

正如您一开始所期望的那样。

代替：

def switch(text = request.values.get("text", None)):

获取方法体中的值：

def switch():
    text = request.values.get("text", None)
    # ... snip ...

【讨论】：