How to Retrieve Submitted Form Values in Flask: Why is request.form Empty?

Passing and Accessing Form Values in Flask

When developing web functionalities, handling form submissions is crucial. To facilitate this process in Flask, you may encounter issues retrieving submitted form values. This article focuses on understanding how to submit values from HTML forms and access them within Flask views.

Problem Statement

Consider the following HTML form:

<code class="html"><form method="POST">
  <input id="my_input" type="text" value="{{ email }}">
  <input id="my_submit" type="submit" value="Submit">
</form></code>

And a corresponding Flask route:

<code class="python">@app.route('/page', methods=['POST', 'GET'])
def get_page():
    if request.method == 'POST':
        print(request.form)  # prints ImmutableMultiDict([])
        print(request.form['my_input'])  # raises 400 error
    return render_template('page.html')</code>

When submitting the form, you may discover that request.form is empty. Attempting to retrieve the value for my_input directly results in a 400 error.

Solution

The crux of the issue lies in the absence of a name attribute in the input fields. For Flask to properly process the form, each input should have a name attribute that corresponds to the desired key in request.form. In this case, the following modification should resolve the issue:

<code class="html"><input name="my_input" id="my_input" type="text" value="{{ email }}"></code>

By adding the name attribute, the input value will be submitted to the server with a key of "my_input". Consequently, you can seamlessly retrieve the value within your Flask view.

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