strange difference in python behavior with Requests, Flask and Kivy

I'm trying to make a simple Kivy app (my first, have patience) that sends two parameters to my localhost (Flask) and gets 2 strings in return. A label should show the string values.

When I don't use Kivy the following code works:

import requests

payload = {'key1': 'value1', 'key2': 'value2'}
r = requests.get('http://127.0.0.1:5000/', params=payload)

print r.text

My console shows me "value1value2". Obviously, because it's the example code I copied from the documentation...

Now, when I put the same code in a Kivy app like this:

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import StringProperty
import requests


kv = '''

BoxLayout:
    orientation: 'vertical'
    Label:
        text: app.text
    Button:
        text: 'call Flask'
        on_press: app.clicked()

'''


class MyApp(App):
    text = StringProperty("Show me the Params!")

    def build(self):
        return Builder.load_string(kv)

    def clicked(self):
        payload = {'key1': 'value1', 'key2': 'value2'}
        r = requests.get('http://127.0.0.1:5000/', params=payload)
        self.text = str(r)
        print r


if __name__ == '__main__':
    MyApp().run()

I get no errors, but the label shows "Response[200]", in stead of the string values ("value1value2")...

I know this is the http status code, but why do I get it here? I want my values! ;-)

Anyone a clue?

Added code (for text entry):

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import StringProperty
import requests


kv = '''

BoxLayout:
    orientation: 'vertical'
    Label:
        text: app.text
    Button:
        text: 'call Flask'
        on_press: app.clicked()
    TextInput:
        id: text_input
'''

class MyApp(App):
    text = StringProperty("Show me the Params!")
    intxt = StringProperty("Input_text")

    def build(self):
        return Builder.load_string(kv)

    def clicked(self):
        payload = {'key1': self.intxt, 'key2': 'value2'}

        r = requests.get('http://127.0.0.1:5000/', params=payload)
        self.text = str(r.content)
        print r.content


if __name__ == '__main__':
    MyApp().run()