Dash + Flask request args

Dash Python
1

In flask, normally you can:

@server.route('/args/')
def args():
   name = request.args.get('name')
   age = request.args.get('age')
   return "name: {}  age: {}".format(name, age)

With a URL like:

http://localhost:8000/args/?name=matt&age=100

(over simplified example)
Currently referenceing the following links:

https://dash.plot.ly/urls

stack overflow discussion

How would this work with dash, because I would like the args from the server.route to get passed into an app.callback?
I really would like to try and integrate the above code, I want to avoid the following:

@app.callback(
[Output('display-name','children'),
Output('display-age','children')]
[Input('url','pathname')])
def load_page(pathname):
    ##parse through the args with regex or str.split()
    return name, age
2

What exactly do you want to avoid in your example? You’ve got the url so you just use Python’s standard library to parse it, e.g.:

import urllib.parse

...

@app.callback(
    [Output('display-name', 'children'), Output('display-age', 'age')]
    [Input('url', 'pathname')]
)
def load_page(url):
    parsed_url = urllib.parse.urlparse(url)
    parsed_query = urllib.parse.parse_qs(parsed_url.query)
    name = parsed_query['name'][0]
    age = parsed_query['age'][0]
    return name, age

You can also get the url using flask.request.headers.get('Referer') but I would not recommend it except for dynamic layouts, you also still need to parse it.

1 Like
3

Ahh great, this is exactly what I was looking for! (In hindsight I should have considered urllib…)

I want to avoid the following

To this I was referring to the bottom portion of my original post

##parse through the args with regex or str.split()

urllib.parse solves this perfectly. Thank you again :smile:

EDIT:
I did want to point out that in testing this with dash, my url was the following: http://localhost:8000/?name=matt&age=1000

Using the code provided above, I debugged what Dash picked up as the input URL in the callback, and also logged the parsed_url and parsed_query objects:

pathname: /
parsed_url: ParseResult(scheme='', netloc='', path='/', params='', query='', fragment='')
parsed_query={}

Thus I changed my URL to: http://localhost:8000/name=matt&age=1000 (note I removed the ‘?’)

So then I had to alter your code slightly:

parsed_url = urllib.parse.urlparse(url[1:])
parsed_query = urllib.parse.parse_qs(parsed_url.path)
2 Likes
5

That’s a very cool trick thank you :slight_smile: .
But if the url was something like http://localhost:8000/results/name=matt&age=1000
then the 1st args would be “results/name” instead of just “name”…
So if you have several url’s in your application it could be confusing…

I kept the same code but I added a “&” to replace the “?” so the urllib can considerate it as an empty args (I use it as a separator)

So for my example the url would be something like http://localhost:8000/results/&name=matt&age=1000
or just http://localhost:8000/results&name=matt&age=1000

1 Like