How to Access Form Values in Flask Routes Without Errors: A Guide to Avoid Empty Dictionaries and 400s

Accessing Form Values in Flask Routes

In Flask applications, posting values from an HTML form and accessing them in views is a common task. However, users often encounter issues with empty request.form dictionaries and 400 errors when trying to access form values by ID.

Key Takeaways:

To successfully post and access form values in Flask:

• Ensure each input field in the HTML form has a unique name attribute. This attribute specifies the key that will be used to identify the corresponding value in the request.form dictionary.
• In the Flask view, retrieve the form values using request.form.get(key_name). This method safely retrieves the value associated with the specified key or returns None if the key does not exist in the dictionary.

Example:

Consider the following HTML form and Flask view:

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

<code class="python">@app.route('/page', methods=['POST', 'GET'])
def get_page():
    if request.method == 'POST':
        my_input_value = request.form.get('my_input')
        # Process my_input_value here
    return render_template('page.html')</code>

By using request.form.get('my_input'), the view safely retrieves the value associated with the 'my_input' key. If the key does not exist in the request.form dictionary, 'None' is returned, preventing 400 errors.

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