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Connecting an application with HTML

Copy hello_lulu.py. Call the new file application_lulu.py. We will edit this file to produce a web application that will display the HTML form when the specified URL is accessed.

Making the application

Inside application_lulu.py, edit the file to look like this:

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

@app_lulu.route('/index_lulu')
def index_lulu():
    return render_template('userinfo_lulu.html')

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

You can try running it now with:

python application_lulu.py

Open a browser window and go to:

127.0.0.1:5000/index_lulu

WOW! It looks PRETTY! Yes, that's the style_lulu.css that we added to the ~/MyFlaskTutorial/static directory. Don't worry about it for now.

You should see the form we just made, with the user information and Submit button. Render_template will look for that HTML template in the ~/MyFlaskTutorial/templates directory. That's why we put it there!

In the hello world example, we saw that these functions must return text (HTML code). The render_template function will return text, and HTML text in fact!

Passing variables to HTML files

You can pass variables to the output HTML through the render_template function. For example, we may want to tell the user how many questions we're going to ask.

To do this, edit the application_lulu.py file:

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

@app_lulu.route('/index_lulu')
def index_lulu():
    nquestions=5
    return render_template('userinfo_lulu.html',num=nquestions)

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

You also need to edit the HTML file to tell it to expect the variable num and to tell it what to do with that information.

Open and edit the file ~/MyFlaskTutorial/templates/userinfo_lulu.html:

<!doctype html>
<title>A short quiz</title>
<link rel=stylesheet type=text/css href='{{ url_for('static',filename='style_lulu.css')}}'>
<div class=page>
  <h1>A short quiz</h1>
  <div class=metanav>
    <h4>
      You will be asked {{num}} questions.
      Please answer them to the best of your ability.
    </h4>

    <form id='userinfoform_lulu' method='post' action='index_lulu' >
      <p>
    Name: <input type='text' name='name_lulu' />
      </p>
      <p>
    Age: <input type='text' name='age_lulu' />
      </p>
      <p>
    <input type='submit' value='Submit' />
      </p>
    </form>

  </div>
</div>

Isn't that awesome? We can pass variables from our backend to the rendered HTML page.

While we're here, take a look at the option called action in the form tag. Do you remember the error we got when we tried to click Submit? It told us it couldn't find a page called index_lulu, right? Here's where we told it to look. If you change this to index_tutu, the error will say:

No webpage was found for the web address: file://localhost/Users/administrator/MyFlaskTutorial/templates/index_tutu
Error 6 (net::ERR_FILE_NOT_FOUND): The file or directory could not be found.

Where is it looking for this file? It's actually looking in application_lulu.py, trying to find a URL among the arguments to the @app_lulu.route() decorators. If the URL is found, it will carry out the function that the decorator decorates (the function immediately below the @app_lulu.route() line). That function will return text (HTML code), and that is the page that will be loaded.

For the time being, in application_lulu.py, we have created a decorated function:

@app_lulu.route('/index_lulu')
def index_lulu():
    ...

So, the webpage CAN be found at 127.0.0.1:5000/index_lulu, and we are telling the client that the webpage to be returned (when Submit is clicked) is userinfo_lulu.html, which can be found in the ~/MyFlaskTutorial/templates

It works so far!

Preparing to learn about POST requests

You might also be curious about these options called name in two of the input tags in the form. These are the identifiers for their respective user-input fields in the form (which we have also named, userinfoform_lulu). Here, we have called the name field name_lulu and we have called the age field age_lulu.

We will need these identifiers as we progress to the next step: understanding POST requests.