test.py

#!/usr/bin/env python
from kivy.app import App
from kivy.animation import Animation
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.button import Button
from kivy.uix.textinput import TextInput

class TestB(App):
    def build(self):
        self.f = FloatLayout()
        self.ti = TextInput(
                pos_hint={'top': 1},
                size_hint=(1, None),
                multiline=False,
                text='1')

        self.b = Button(size_hint=(None, None))
        self.b.bind(on_press=self.moveit)
        self.f.add_widget(self.ti)
        self.f.add_widget(self.b)

        return self.f

    def moveit(self, *args):
        try:
            duration = float(self.ti.text)

            if duration <= 0:
                raise ValueError

            a = Animation(x=self.f.right, d=duration)
            a += Animation(x=0, d=duration)

            a.start(self.b)

        except ValueError:
            self.ti.text = 'please put a valid positive float number'

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