Added code

ui/modules/validators/__init__.py

@@ -0,0 +1,2 @@
+from .page_text import *
+from .page_index import *

ui/modules/validators/page_index.py

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+from ui.modules.updaters.page_index import update_page_text
+from ui.gui import Ui_MainWindow
+from PyQt5 import QtGui
+
+
+def validate_page_index(ui: Ui_MainWindow, event: QtGui.QKeyEvent, old_event):
+    old_event(event)
+    for char in ui.page_index.text():
+        if char not in '0123456789':
+            ui.page_index.setText(''.join(c for c in ui.page_index.text() if c in '0123456789'))
+            ui.page_index.setCursorPosition(QtGui.QTextCursor.End)
+            break
+
+    update_page_text(ui)

ui/modules/validators/page_text.py

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+from ui.modules.updaters.page_text import update_page_index
+from modules.config import charset
+from ui.gui import Ui_MainWindow
+from PyQt5 import QtGui
+
+
+def validate_page_text(ui: Ui_MainWindow, event: QtGui.QKeyEvent, old_event):
+    old_event(event)
+    for char in ui.page_text.toPlainText():
+        if char not in charset:
+            ui.page_text.setPlainText(''.join(c for c in ui.page_text.toPlainText() if c in charset))
+            ui.page_text.moveCursor(QtGui.QTextCursor.End)
+            break
+
+    update_page_index(ui)