4_requests.rst

All about requests

A request is made when a user visits a URL. There are a few different types (also called methods) of requests. Here, we will only discuss two types: GET and POST requests.

The request module must be imported from flask. You can update the import line in application_lulu.py:

from flask import Flask,render_template,request

The request module has an attribute called method, which only has a value if a request is made. When the request is made, it takes the value of GET or POST (or a few other possible values, but we are ignoring them, remember?).

There is some amount of philosophical argument about when to use GET and when to use POST. From what I can tell, GET definitely should be used when no user-information is being used to produce the page. (Think Web 1.0.) And, POST should be used when the user is sending information to the server before a page is returned.

(Technically, one can receive user input through the GET request, but it would appear only in the URL string. For example, do a Google search and see the URL you are visiting when your search result returns. There are question marks, key/value pairs, and other things that define the search.)

GET requests

In the application we have written so far, we have just done a GET request. We have asked for a webpage at 127.0.0.1:5000/index_lulu. Then application_lulu.py found the correct function to call, and it returned a webpage (~/MyFlaskTutorial/templates/userinfo_lulu.html).

In the function index_lulu (inside application_lulu.py), the attribute request.method exists, and it is equal to GET.

Edit application_lulu.py and see that this does not change what we have done so far:

from flask import Flask,render_template
app_lulu = Flask(__name__)

@app_lulu.route('/index_lulu',methods=['GET'])
def index_lulu():
    nquestions=5
if request.method == 'GET':
        return render_template('userinfo_lulu.html',num=nquestions)
    else:
        return 'request.method was not a GET!'

if __name__ == "__main__":
    app_lulu.run(debug=True)

Note that we instruct the application which types of requests to accept in the line:

@app_lulu.route('/index_lulu',methods=['GET'])

I hope that worked for you just as well as it worked for me! CELEBRATE! We're almost there!

POST requests ------------

Try entering your name and age in the fields, then click on Submit. It didn't work, did it? That's because we did not allow POST requests for the destination /index_lulu. This can be remedied by editing the line in application_lulu.py to:

@app_lulu.route('/index_lulu',methods=['GET','POST'])

If you try running the application again, when you try to Submit your name and age, you should get the text we specified above:

'request.method was not a GET!'

GOOD! We know what's getting called when. (At least, I think you should know, based on our tests so far!)

But, it's not interesting to have the screen tell you it was not a GET request. We'd rather the application CALCULATE SOME STUFF or at least RETURN A DIFFERENT PAGE when a POST request is received.

Let's have it return a page with questions on it. First, we will need to make the HTML template, then we will have to instruct the application to use that template. The next part of the tutorial will discuss this.