Question

I can’t find a solution anywhere how to handle module import exceptions. I need to import ‘enchant’ module but I have to check if it’s installed first. And I need to show an error message if it’s not installed. So if I do this, there’s no way to show the QMessageBox because the main class hasn’t been created yet.

import sys
import re

from PyQt4.QtCore import *
from PyQt4.QtGui import *

try:
    import enchant
    dict_list = enchant.list_languages()
    if "ru_RU" in dict_list:
        self.dict = enchant.Dict("ru_RU")
    else:
        self.dict = enchant.Dict()
except ImportError, inst:
    #How do I graphically show an error message here if the class hasn't been set up yet?

class Translit(QMainWindow):
    def __init__(self, parent = None):
        super(Translit, self).__init__(parent)

If I do this:

import sys
import re

from PyQt4.QtCore import *
from PyQt4.QtGui import *

class Translit(QMainWindow):
    def __init__(self, parent = None):
        super(Translit, self).__init__(parent)

    try:
        import enchant
        dict_list = enchant.list_languages()
        if "ru_RU" in dict_list:
            self.dict = enchant.Dict("ru_RU")
        else:
            self.dict = enchant.Dict()
    except ImportError, inst:
        QMessageBox.warning(parent, "", "Error:\n%s seems to be installed\n\nSpell checking will be disabled" % (inst))

    self.change_dict()

    def change_dict(self):
        self.dict = enchant.Dict("en_US")
        QMessageBox.about(parent,"","Spellcheck is set to " + self.dict.tag)

then the interpreter complains “NameError: global name ‘enchant’ is not defined”.

Please show me how I can show module import exception messages or how to make that module work throughout the whole program. Thank you.

Here’s an original source I’m trying to reuse:

__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("ru_RU")
    self.highlighter = Highlighter(self.document())
    self.highlighter.setDict(self.dict)

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()
    cursor.select(QTextCursor.WordUnderCursor)
    self.setTextCursor(cursor)

    # 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)
                action.correct.connect(self.correctWord)
                spell_menu.addAction(action)
            # Only add the spelling suggests to the menu if there are
            # suggestions.
            if len(spell_menu.actions()) != 0:
                popup_menu.insertSeparator(popup_menu.actions()[0])
                popup_menu.insertMenu(popup_menu.actions()[0], spell_menu)

    popup_menu.exec_(event.globalPos())

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

    cursor.removeSelectedText()
    cursor.insertText(word)

    cursor.endEditBlock()

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:
        return

    text = unicode(text)

    format = QTextCharFormat()
    format.setUnderlineColor(Qt.red)
    format.setUnderlineStyle(QTextCharFormat.SpellCheckUnderline)

    for word_object in re.finditer(self.WORDS, text):
        if not self.dict.check(word_object.group()):
            self.setFormat(word_object.start(),
                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(
        unicode(self.text())))

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

spellEdit = SpellTextEdit()
spellEdit.show()

return app.exec_()

if __name__ == '__main__':
    sys.exit(main()) 

Answer 1

Here’s one possible fix for your problem:

from PyQt4.QtCore import *
from PyQt4.QtGui import *

try:
    import enchant
except ImportError:
    enchant = None

class Translit(QMainWindow):
    def __init__(self, parent = None):
        super(Translit, self).__init__(parent)
        if enchant is not None:
            dict_list = enchant.list_languages()
            if "ru_RU" in dict_list:
                self.dict = enchant.Dict("ru_RU")
            else:
                self.dict = enchant.Dict()
            self.change_dict()
        else:
            self.dict = None
            QMessageBox.warning(parent, "",
                "Error: could not import the 'enchant' module\n\n"
                "Spell checking will be disabled")

    def change_dict(self):
        if self.dict is not None:
            self.dict = enchant.Dict("en_US")
            QMessageBox.about(
                parent, "", "Spellcheck is set to " + self.dict.tag)

However, if spell checking is an optional feature, as a user I would be pretty annoyed if I got this warning message every time I ran the application.

It would be better show the warning when the user first tries to access the spell checker (and then disable any further access). But the way to go about doing that will obviously depend on how the enchant module is used elsewhere within your application.