SyntaxHighlighter problem

I have found some code of syntax highlight in PyQt4, but my problem is that QTextEdit colorize text, but only first line, and only line when I put enter at the end of line at the following lines. If I open file with code, only first line is colorized. Rest of code is black.

Would you be so kind to help me?

Code:

class Highlighter(QtCore.QObject):
    def __init__(self, parent=None):
        QtCore.QObject.__init__(self, parent)
 
        self.mappings = {}
 
    def addToDocument(self, doc):
        self.connect(doc, QtCore.SIGNAL("contentsChange(int, int, int)"), self.highlight)
 
    def addMapping(self, pattern, format):
        self.mappings[pattern] = format
 
    def highlight(self, position, removed, added):
        doc = self.sender()
 
        block = doc.findBlock(position)
        if not block.isValid():
            return
 
        endBlock = QtGui.QTextBlock()
        if added > removed:
            endBlock = doc.findBlock(position + added)
        else:
            endBlock = block
 
        while block.isValid() and not (endBlock < block):
            self.highlightBlock(block)
            block = block.next()
 
    def highlightBlock(self, block):
        layout = block.layout()
        text = block.text()
 
        overrides = []
 
        for pattern in self.mappings:
            expression = QtCore.QRegExp(pattern)
            i = text.indexOf(expression)
            while i >= 0:
                range = QtGui.QTextLayout.FormatRange()
                range.start = i
                range.length = expression.matchedLength()
                range.format = self.mappings[pattern]
                overrides.append(range)
 
                i = text.indexOf(expression, i + expression.matchedLength())
 
        layout.setAdditionalFormats(overrides)
        block.document().markContentsDirty(block.position(), block.length())