QPlainTextEdit With In Line Spell Check

***Update: Simplified Highlighter.highlightBlock function

One thing Qt lacks is an integrated spell check in the text entry components. For a project I’m working on this is necessary. Using python-enchant and the QSyntaxHighlighter I was able to implement this functionality. Here is how to add an in line spell check support to a QPlainTextEdit.

#!/usr/bin/env python
# -*- coding: utf-8 -*-

__license__ = 'MIT'
__copyright__ = '2009, John Schember '
__docformat__ = 'restructuredtext en'

import re
import sys

import enchant

from PyQt4.Qt import QAction
from PyQt4.Qt import QApplication
from PyQt4.Qt import QEvent
from PyQt4.Qt import QMenu
from PyQt4.Qt import QMouseEvent
from PyQt4.Qt import QPlainTextEdit
from PyQt4.Qt import QSyntaxHighlighter
from PyQt4.Qt import QTextCharFormat
from PyQt4.Qt import QTextCursor
from PyQt4.Qt import Qt
from PyQt4.QtCore import pyqtSignal

class SpellTextEdit(QPlainTextEdit):

    def __init__(self, *args):
        QPlainTextEdit.__init__(self, *args)

        # Default dictionary based on the current locale.
        self.dict = enchant.Dict()
        self.highlighter = Highlighter(self.document())

    def mousePressEvent(self, event):
        if event.button() == Qt.RightButton:
            # Rewrite the mouse event to a left button event so the cursor is
            # moved to the location of the pointer.
            event = QMouseEvent(QEvent.MouseButtonPress, event.pos(),
                Qt.LeftButton, Qt.LeftButton, Qt.NoModifier)
        QPlainTextEdit.mousePressEvent(self, event)

    def contextMenuEvent(self, event):
        popup_menu = self.createStandardContextMenu()

        # Select the word under the cursor.
        cursor = self.textCursor()

        # Check if the selected word is misspelled and offer spelling
        # suggestions if it is.
        if self.textCursor().hasSelection():
            text = unicode(self.textCursor().selectedText())
            if not self.dict.check(text):
                spell_menu = QMenu('Spelling Suggestions')
                for word in self.dict.suggest(text):
                    action = SpellAction(word, spell_menu)
                # Only add the spelling suggests to the menu if there are
                # suggestions.
                if len(spell_menu.actions()) != 0:
                    popup_menu.insertMenu(popup_menu.actions()[0], spell_menu)


    def correctWord(self, word):
        Replaces the selected text with word.
        cursor = self.textCursor()



class Highlighter(QSyntaxHighlighter):

    WORDS = u'(?iu)[\w\']+'

    def __init__(self, *args):
        QSyntaxHighlighter.__init__(self, *args)

        self.dict = None

    def setDict(self, dict):
        self.dict = dict

    def highlightBlock(self, text):
        if not self.dict:

        text = unicode(text)

        format = QTextCharFormat()

        for word_object in re.finditer(self.WORDS, text):
            if not self.dict.check(word_object.group()):
                    word_object.end() - word_object.start(), format)

class SpellAction(QAction):

    A special QAction that returns the text in a signal.

    correct = pyqtSignal(unicode)

    def __init__(self, *args):
        QAction.__init__(self, *args)

        self.triggered.connect(lambda x: self.correct.emit(

def main(args=sys.argv):
    app = QApplication(args)

    spellEdit = SpellTextEdit()

    return app.exec_()

if __name__ == '__main__':

The SpellTextEdit’s purpose is straightforward. It will mark misspelled words. Right clicking on a word in the SpellTextEdit will cause the word to become selected and display a context menu. If the word is misspelled and there are spelling suggestions the context menu will include a sub menu of those suggestions. Selecting a suggestion will replace the misspelled text with the selection.

The Highlighter class takes text, breaks it into words, checks if they are spelled correctly and if not underlines the misspelled ones with a red squiggle. I’m using a regular expression to split the words instead of using str.split because str.split will only split on whitespace and include punctuation (e.g. “.!*) as part of the words.

SpellAction is a simple class that allows for the action’s text to be sent with the signal. This is necessary for dynamically creating the list of possible correction words in the right click menu. The SpellAction is connected to a function that replaces the selected text with the signal text.

3 thoughts on “QPlainTextEdit With In Line Spell Check

  1. Thanks… This is great…

    I had some problems importing pyqtSignal though… Ubuntu 9.04, Qt 4.5.

    Nevertheless, replacing the custom SpellAction with a normal Action connected to a partial function did the trick:
    action = QAction(suggestion, spell_menu)
    action.connect(action, SIGNAL(“triggered()”), functools.partial(self.correctWord, word = suggestion))

    Don’t know if this approach is better, but it worked for me…

    And again thanks for publishing this… Otherwise this would not be a feature I’d waste time on 🙂
    (But it’s just so neat to have…)

  2. The reason you can’t import pyqtSignal is because it is only available in PyQt 4.5+. While, Ubuntu 9.04 ships with Qt 4.5, it only ships with PyQt 4.4.4. The partial solution still works fine and is probably the cleanest solution for PyQt 4.4.

  3. Hi,

    Just realized that instead of overwriting the mousePressEvent on the Q(Plain)TextEdit an convert right clicks to left clicks inorder to move the cursor… Which is sort of an ugly hack, you can use QPlainTextEdit.cursorForPosition(QPoint)

    cursor = self.cursorForPosition(event.pos())
    instead of cursor = self.textCursor() in the contextMenuEvent implementation, this also means that the visible text cursor won’t move, and the user will not see that the text is selected…
    This could still be achieved though, by calling self.setTextCursor(cursor)

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