Using staticmethod

_main-03.py

from asciimatics.screen import Screen
from asciimatics.scene import Scene
from asciimatics.widgets import Layout, Frame, Button, Text

class TestView(Frame):
    def __init__(self, screen):
        super().__init__(screen,
                         screen.height * 2 // 3,
                         screen.width * 2 // 3,
                         reduce_cpu=True,
                         )

        self._create_layouts()

    def _create_layouts(self):
        top_layout = Layout([5, 1, 1])
        self.add_layout(top_layout)

        top_layout.add_widget(Text(label="Filter"))

        self.text_count = Text(label="Count",
                               validator=self._is_digit)  # validador should to call function with func(new_char)
        top_layout.add_widget(self.text_count, 1)

        top_layout.add_widget(Button("Back", lambda x: x), 2)
        self.fix()

    @staticmethod
    def _is_digit(self, new_char):
        # valid new char
        # and insert with self.
        if new_char.isdigit():
            self.text_count.value = new_char
            return True


def main(screen):
    scenes = [
        Scene([TestView(screen)], name="test"),

    ]
    screen.play(scenes)


if __name__ == "__main__":
    Screen.wrapper(main)
    
"""
(venv) franklin@slhost:~/PycharmProjects/viewerpackages$ python _main.py 
Traceback (most recent call last):
  File "_main.py", line 46, in <module>
    Screen.wrapper(main)
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/screen.py", line 1169, in wrapper
    func(screen)
  File "_main.py", line 42, in main
    screen.play(scenes)
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/screen.py", line 1343, in play
    scenes, unhandled_input=unhandled_input, start_scene=start_scene)
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/screen.py", line 1406, in set_scenes
    old_scene=start_scene, screen=self)
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/scene.py", line 44, in reset
    effect.reset()
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/widgets.py", line 552, in reset
    self.data = deepcopy(self._initial_data)
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/widgets.py", line 475, in data
    layout.update_widgets()
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/widgets.py", line 1162, in update_widgets
    widget.value = widget.value
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/widgets.py", line 1680, in value
    self._set_and_check_value(new_value, reset=True)
  File "/home/franklin/PycharmProjects/viewerpackages/venv/lib64/python3.6/site-packages/asciimatics/widgets.py", line 1692, in _set_and_check_value
    self._is_valid = self._validator(self._value)
TypeError: _is_digit() missing 1 required positional argument: 'new_char'
    
"""