python - Using requests module in flask route function

Question

Consider the following minimal working flask app:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello():
    return "I am /"

@app.route("/api")
def api():
    return "I am /api"

if __name__ == "__main__":
    app.run()

This happily works. But when I try to make a GET request with the "requests" module from the hello route to the api route - I never get a response in the browser when trying to access http://127.0.0.1:5000/

from flask import Flask
import requests

app = Flask(__name__)

@app.route("/")
def hello():
    r = requests.get("http://127.0.0.1:5000/api")
    return "I am /" # This never happens :(

@app.route("/api")
def api():
    return "I am /api"

if __name__ == "__main__":
    app.run()

So my questions are: Why does this happen and how can I fix this?

Answer 1

You are running your WSGI app with the Flask test server, which by default uses a single thread to handle requests. So when your one request thread tries to call back into the same server, it is still busy trying to handle that one request.

You'll need to enable threading:

if __name__ == "__main__":
    app.run(threaded=True)

or use a more advanced WSGI server; see Deployment Options.