問題描述：當在python的flask中定義全局變量之后，當其他模塊修改全局變量，flask中的api運行時讀取的全局變量值還是定義時的初始值。
在https://stackoverflow.com/questions/23457658/flask-global-variables有人遇到了同樣的問題。
I am trying to find out how to work with global variables in Flask:
gl = {'name': 'Default'}
@app.route('/store/<name>')
def store_var(name=None):
gl['name'] = name
return "Storing " + gl['name']
@app.route("/retrieve")
def retrieve_var():
n = gl['name']
return "Retrieved: " + n
Storing the name and retrieving it from another client works fine. However, this doesn't feel right: a simple global dictionary where any session pretty much simultaneously can throw in complex objects, does that really work without any dire consequences?
下面有人說了導致問題的原因：
No, it doesn't work, not outside the simple Flask development server.
WSGI servers scale in two ways; by using threads or by forking the process. A global dictionary is not a thread-safe storage, and when using multi-processing changes to globals are not going to be shared. If you run this on a PAAS provider like Google App Server, the processes aren't even forked; they are run on entirely separate machines even.
可能的解決方法：
Use some kind of backend storage instead; a memcached server, a database server, something to control concurrent access and share the data across processes.
另一個可能的解決方法：
參考：https://www.cnpython.com/qa/78502
你不需要一個全局變量來實現這一點，並且說真的，你在未來的任何時候都不需要它們，因為使用全局變量是一種不好的做法。有關詳細信息，請參閱此鏈接，why are global variables evil?
現在談到您的問題，您可能需要flask的g模塊，該模塊創建一個上下文，該上下文在同一用戶的多個請求上保持不變。你可以這樣做：
from flask import g
...
def get_messages():
messages = getattr(g, '_messages', None)
if messages is None:
g._messages = [] # to store messages you may use a dictionary
return g._messages
def add_message(message):
messages = get_messages()
messages.append(message)
setattr(g, '_messages', messages)
return messages
記住，對於每個用戶，應用程序都會創建一個不同的線程，這樣既不會共享變量，也不會共享它們的值。因此，對於每個用戶，都有一個不同的g，但它將在同一個用戶的多個請求上持續存在。希望有幫助！