Short example showing smarter filtering in Qt

qt_filter_example.py

from difflib import SequenceMatcher
try:
    from PySide6 import QtCore, QtGui, QtWidgets
except ImportError:
    from PySide2 import QtCore, QtGui, QtWidgets


class FilterModel(QtCore.QSortFilterProxyModel):
    """ A simple filter model based on sequencematcher quick_ratio.
    ratio is 0-1 value for a match.

    Note: This is not performant, it is an example, ideally you would look into precaching or difflib.get_close_matches() for many items
    https://docs.python.org/3/library/difflib.html
    """
    def __init__(self, ratio:float=0.6, parent=None):
        super().__init__(parent)
        self._filter_text = ""
        self._ratio = ratio
        self._show_all = False
        self.sort(0, QtCore.Qt.AscendingOrder)
    
    @QtCore.Slot(str)
    def set_filter_text(self, text:str):
        self._filter_text = str(text).lower()
        self.invalidate()
    
    @QtCore.Slot(float)
    def set_ratio(self, ratio:float):
        self._ratio = float(ratio)
        self.invalidate()
    
    @QtCore.Slot(bool)
    def set_show_all(self, show_all:bool):
        self._show_all = bool(show_all)
        self.invalidate()
    
    def filterAcceptsColumn(self, source_column:int, source_parent:QtCore.QModelIndex)->bool:
        return True
    
    def filterAcceptsRow(self, source_row:int, source_parent:QtCore.QModelIndex)->bool:
        if self._ratio <= 0.0 or self._show_all or not self._filter_text:
            # Nothing set, show everything
            return True
        
        # Case-insensitive
        text = (self.sourceModel().index(source_row, 0, source_parent).data() or "").lower()
        if not text:
            return False
        if self._filter_text in text:
            return True
        # First parameter is optional filtering of "junk" text like spaces, default is usually fine.
        # ratio is more accurate but doesn't provide much in this context, real_quick_ratio is not accurate enough.
        ratio = SequenceMatcher(None, self._filter_text, text).quick_ratio()
        return ratio >= self._ratio

    def lessThan(self, left:QtCore.QModelIndex, right:QtCore.QModelIndex)->bool:
        if not self._filter_text or self._show_all:
            return left.row() < right.row()
        
        left_ratio = SequenceMatcher(None, self._filter_text, left.data().lower()).quick_ratio() if left.data() else 0.0
        right_ratio = SequenceMatcher(None, self._filter_text, right.data().lower()).quick_ratio() if right.data() else 0.0
        # Sort text ascending so ratio is flipped
        return left_ratio > right_ratio
    
    def data(self, index, role=QtCore.Qt.DisplayRole):
        # Provides a color falloff to demonstrate the filtering
        if not self._show_all or role != QtCore.Qt.ForegroundRole or self._ratio <= 0.0:
            return super().data(index, role)
        ratio = SequenceMatcher(None, self._filter_text, (index.data() or "").lower()).quick_ratio()
        if ratio < self._ratio:
            # Draw falloff color between 20 (no match) and 255 (full match)
            t = ratio * (1.0/self._ratio)
            luminance = (1 - t) * 20 + t * 255

            return QtGui.QBrush(QtGui.QColor(luminance, luminance, luminance))
        return super().data(index, role)
        
        


class Widget(QtWidgets.QWidget):
    """ A Simple example widget that filters items based on some text input
    """
    def __init__(self, items, parent=None):
        super().__init__(parent)
        self.setWindowTitle("Filter Example")
        
        layout = QtWidgets.QVBoxLayout(self)
        
        search_box = QtWidgets.QLineEdit()
        search_box.setPlaceholderText("filter...")
        layout.addWidget(search_box)
        
        show_all_box = QtWidgets.QCheckBox("Show All")
        layout.addWidget(show_all_box)
        
        view = QtWidgets.QListView()
        layout.addWidget(view)
        
        model = QtCore.QStringListModel(items, parent=self)
        filter_model = FilterModel(parent=self)
        filter_model.setSourceModel(model)
        view.setModel(filter_model)
        
        search_box.textChanged.connect(filter_model.set_filter_text)
        show_all_box.toggled.connect(filter_model.set_show_all)


items = ["January", "February", "March", "April", "May", "June", "July", "August", "October", "November", "December"]

widget = Widget(items)
widget.show()