yamltest.py

#!/usr/bin/env python3

import kivy
kivy.require('2.0.0')

from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.app import App
from kivy.properties import ObjectProperty, StringProperty
import subprocess as sp

ruby = sp.run(['which', 'ruby'], capture_output=True).stdout.strip()

kv = """
<MainScreen>:
    orientation: 'vertical'
    TextInput:
        on_text: root.process(self.text)
    TextInput:
        id: output
"""
Builder.load_string(kv)


class MainScreen(BoxLayout):
    pass

    def process(self, yaml):
        global ruby
        code = f"print YAML.load('{yaml}').to_yaml.sub(/---\\n?/, '')"
        res = sp.run([ruby, '-ryaml', '-e', code], capture_output=True)
        outfield = self.ids.output
        if res.stdout:
            utf8_str = res.stdout.decode('UTF-8')
            print(utf8_str)
            outfield.text = utf8_str.strip()
            outfield.foreground_color = (.17,.37,0, 1)
        elif res.stderr:
            outfield.text = res.stderr.strip()
            outfield.foreground_color = (.67,0,.3, 1)


class YAMLTest(App):
    def build(self):
        return MainScreen()


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