Updating DataFrame while API is running in Python-CodePudding

So I am trying to create an API that constantly reads from a CSV and returns information about it when requested. So far, I have created a flask API that reads the CSV file once and returns correctly. However, I can't seem to make it constantly update. My working code is something like this.

app = flask.Flask(__name__)
app.config["DEBUG"] = True


dfchat = pd.read_csv(path)
escaper = None

# for now, this is just to make sure the program keeps running even if there is an error
def escape_route():
    global escaper
    while escaper != "Y":
        escaper = str(input("Exit now? Enter \'Y\': \n")).strip()
    os._exit(os.X_OK)
    
def sample_function(dfchat):

    @app.route('/sample_text', methods=['GET'])
    def sample_endpoint():
        # this function filters dfchat and returns whatever

def main():
    global dfchat
    escape_route_thread = threading.Thread(target = escape_route)
    escape_route_thread.start()
    sample_function(dfchat)
    app.run()


main()

I have tried creating another thread that updates the CSV file:

def retrieve_database():
    global dfchat
    while True:
        time.sleep(0.1)
        dfchat = pd.read_csv(path)

along with:

escape_route_thread = threading.Thread(target = retrieve_database)
escape_route_thread.start()

in the main function.

But that fails to update the dfchat data frame when the API launches. I have tested the thread by itself and it does update and return an updated data frame. From what I understand so far, once an API runs, python code cannot change the API itself.

So, Is there a way to update a running API with just python?

I'm asking for just python because I will not be able to manually enter a link like "/refresh" to do this. It has to be done by python.

Am I missing something?

Thank you very much for helping!

Edit:

I also tried to update the csv file for every API call. But that does but work either:

def sample_function():

    dfchat = pd.read_csv(path)
    @app.route('/sample_text', methods=['GET'])
    def sample_endpoint():
        # this function filters dfchat and returns whatever

CodePudding user response：

So I realized that the solution is really simple. I'm new to CS and APIs in general so I did not realize how @app.route worked in Flask. Outside of @app.route cannot change a route but updating a variable inside a route does work. I accidentally kept updating dfchat outside of @app.route.

def sample_function():

  # instead of putting dfchat here
  @app.route('/sample_text', methods=['GET'])
  def sample_endpoint():
      dfchat = pd.read_csv(path) # it should go here.
      # this function filters dfchat and returns whatever

Thank you yco for helping me realize this.

CodePudding user response：

Code defined at the root of the script (as was dfchat definition in your example) is executed once at the moment you start the flask server.

Code inside a Flask app route (function decorated with @app.route(...)) is executed at each API call to this route.

from flask import Flask

app = Flask(__name__)

path = "path/to/your/csv/file.csv"

@app.route('/sample_text', methods=['GET'])
def sample_endpoint():
  dfchat = pd.read_csv(path)
  # do what you have to do with the DF

Also note that Flask handles errors without stopping the API, and has great documentation to help you : https://flask.palletsprojects.com/en/2.0.x/quickstart/#a-minimal-application