When using flash, the code ends automatically without an error, the connection cannot be maintained, and the URL cannot be accessed.

author ：cyl

Time ：2021.11.3

One 、 Error description

Learning to use python Lightweight web The service , come to know flask library . But there was a problem executing an entry-level code ：

from flask import Flask # Import flask library 

app = Flask(__name__) # establish flask example 


# Use app.route Modifier to define a url, When visiting this url You can automatically call the function under the modifier （ My personal current understanding , Not necessarily ）
@app.route("/a")
def testflask():
    print("hello world")
    return 'Hello World!'


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)# Start port , perform app.run You can start the service . Default Flask Only listen to the local of the virtual machine 127.0.0.1 This address , Port is 5000. Using parameters instead 0.0.0.0 Can listen to all ports .

In principle , The correct result of running after execution is ：

It's a case of keeping connected .

But mine is ：

Although executed correctly, it automatically ends execution .

Two 、 The reason for the error

I didn't have this problem because python Wrong version or flask Wrong version . But because python Will automatically test The first function is executed as a test . In fact, the information returned from the above figure can also be seen .（ It seems that naming can't be fooled ,python Many constraints are easy to use ）

3、 ... and 、 Error resolution

Change function name

Perfect execution

Although the reason for the error is different from the title of my article . Just take a look at that .

If it helps you , Do me a favor