QSyntaxHighlighter

The QSyntaxHighlighter class allows you to define syntax highlighting rules, and in addition you can use the class to query a document’s current formatting or user data. More

Inheritance diagram of PySide2.QtGui.QSyntaxHighlighter

Synopsis

Functions

Virtual functions

Slots

Detailed Description

The QSyntaxHighlighter class is a base class for implementing QTextDocument syntax highlighters. A syntax highligher automatically highlights parts of the text in a QTextDocument . Syntax highlighters are often used when the user is entering text in a specific format (for example source code) and help the user to read the text and identify syntax errors.

To provide your own syntax highlighting, you must subclass QSyntaxHighlighter and reimplement highlightBlock() .

When you create an instance of your QSyntaxHighlighter subclass, pass it the QTextDocument that you want the syntax highlighting to be applied to. For example:

editor = QTextEdit()
highlighter = MyHighlighter(editor.document())

After this your highlightBlock() function will be called automatically whenever necessary. Use your highlightBlock() function to apply formatting (e.g. setting the font and color) to the text that is passed to it. QSyntaxHighlighter provides the setFormat() function which applies a given QTextCharFormat on the current text block. For example:

class MyHighlighter(QSyntaxHighlighter):
    def highlightBlock(self, text):
        myClassFormat = QTextCharFormat()
        myClassFormat.setFontWeight(QFont.Bold)
        myClassFormat.setForeground(Qt.darkMagenta)
        pattern = QString("\\bMy[A-Za-z]+\\b")

        expression = QRegExp(pattern)
        index = text.indexOf(expression)
        while index >= 0:
            length = expression.matchedLength()
            setFormat(index, length, myClassFormat)
            index = text.indexOf(expression, index + length)

Some syntaxes can have constructs that span several text blocks. For example, a C++ syntax highlighter should be able to cope with / *...* / multiline comments. To deal with these cases it is necessary to know the end state of the previous text block (e.g. “in comment”).

Inside your highlightBlock() implementation you can query the end state of the previous text block using the previousBlockState() function. After parsing the block you can save the last state using setCurrentBlockState() .

The currentBlockState() and previousBlockState() functions return an int value. If no state is set, the returned value is -1. You can designate any other value to identify any given state using the setCurrentBlockState() function. Once the state is set the QTextBlock keeps that value until it is set set again or until the corresponding paragraph of text is deleted.

For example, if you’re writing a simple C++ syntax highlighter, you might designate 1 to signify “in comment”:

multiLineCommentFormat = QTextCharFormat()
multiLineCommentFormat.setForeground(Qt.red)

startExpression = QRegExp("/\\*")
endExpression = QRegExp("\\*/")

setCurrentBlockState(0)

startIndex = 0
if previousBlockState() != 1:
    startIndex = text.indexOf(startExpression)

while startIndex >= 0:
    endIndex = text.indexOf(endExpression, startIndex)
    if endIndex == -1:
       setCurrentBlockState(1)
       commentLength = text.length() - startIndex
    else:
       commentLength = endIndex - startIndex
                       + endExpression.matchedLength()

    setFormat(startIndex, commentLength, multiLineCommentFormat)
    startIndex = text.indexOf(startExpression,
                              startIndex + commentLength)

In the example above, we first set the current block state to 0. Then, if the previous block ended within a comment, we highlight from the beginning of the current block (startIndex = 0 ). Otherwise, we search for the given start expression. If the specified end expression cannot be found in the text block, we change the current block state by calling setCurrentBlockState() , and make sure that the rest of the block is highlighted.

In addition you can query the current formatting and user data using the format() and currentBlockUserData() functions respectively. You can also attach user data to the current text block using the setCurrentBlockUserData() function. QTextBlockUserData can be used to store custom settings. In the case of syntax highlighting, it is in particular interesting as cache storage for information that you may figure out while parsing the paragraph’s text. For an example, see the setCurrentBlockUserData() documentation.

See also

QTextDocument Syntax Highlighter Example

class QSyntaxHighlighter(parent)

QSyntaxHighlighter(parent)

param parent

QObject

Constructs a QSyntaxHighlighter with the given parent .

If the parent is a QTextEdit , it installs the syntax highlighter on the parents document. The specified QTextEdit also becomes the owner of the QSyntaxHighlighter .

Constructs a QSyntaxHighlighter and installs it on parent . The specified QTextDocument also becomes the owner of the QSyntaxHighlighter .

PySide2.QtGui.QSyntaxHighlighter.currentBlock()
Return type

QTextBlock

Returns the current text block.

PySide2.QtGui.QSyntaxHighlighter.currentBlockState()
Return type

int

Returns the state of the current text block. If no value is set, the returned value is -1.

PySide2.QtGui.QSyntaxHighlighter.currentBlockUserData()
Return type

QTextBlockUserData

Returns the QTextBlockUserData object previously attached to the current text block.

PySide2.QtGui.QSyntaxHighlighter.document()
Return type

QTextDocument

Returns the QTextDocument on which this syntax highlighter is installed.

See also

setDocument()

PySide2.QtGui.QSyntaxHighlighter.format(pos)
Parameters

posint

Return type

QTextCharFormat

Returns the format at position inside the syntax highlighter’s current text block.

See also

setFormat()

PySide2.QtGui.QSyntaxHighlighter.highlightBlock(text)
Parameters

text – unicode

Highlights the given text block. This function is called when necessary by the rich text engine, i.e. on text blocks which have changed.

To provide your own syntax highlighting, you must subclass QSyntaxHighlighter and reimplement . In your reimplementation you should parse the block’s text and call setFormat() as often as necessary to apply any font and color changes that you require. For example:

class MyHighlighter(QSyntaxHighlighter):
    def highlightBlock(self, text):
        myClassFormat = QTextCharFormat()
        myClassFormat.setFontWeight(QFont.Bold)
        myClassFormat.setForeground(Qt.darkMagenta)
        pattern = QString("\\bMy[A-Za-z]+\\b")

        expression = QRegExp(pattern)
        index = text.indexOf(expression)
        while index >= 0:
            length = expression.matchedLength()
            setFormat(index, length, myClassFormat)
            index = text.indexOf(expression, index + length)

See the Detailed Description for examples of using setCurrentBlockState() , currentBlockState() and previousBlockState() to handle syntaxes with constructs that span several text blocks

PySide2.QtGui.QSyntaxHighlighter.previousBlockState()
Return type

int

Returns the end state of the text block previous to the syntax highlighter’s current block. If no value was previously set, the returned value is -1.

PySide2.QtGui.QSyntaxHighlighter.rehighlight()

Reapplies the highlighting to the whole document.

PySide2.QtGui.QSyntaxHighlighter.rehighlightBlock(block)
Parameters

blockQTextBlock

Reapplies the highlighting to the given QTextBlock block .

See also

rehighlight()

PySide2.QtGui.QSyntaxHighlighter.setCurrentBlockState(newState)
Parameters

newStateint

Sets the state of the current text block to newState .

PySide2.QtGui.QSyntaxHighlighter.setCurrentBlockUserData(data)
Parameters

dataQTextBlockUserData

Attaches the given data to the current text block. The ownership is passed to the underlying text document, i.e. the provided QTextBlockUserData object will be deleted if the corresponding text block gets deleted.

QTextBlockUserData can be used to store custom settings. In the case of syntax highlighting, it is in particular interesting as cache storage for information that you may figure out while parsing the paragraph’s text.

For example while parsing the text, you can keep track of parenthesis characters that you encounter (‘{[(‘ and the like), and store their relative position and the actual QChar in a simple class derived from QTextBlockUserData :

class MyHighlighter(QSyntaxHighlighter):
    def highlightBlock(self, text):
        myClassFormat = QTextCharFormat()
        myClassFormat.setFontWeight(QFont.Bold)
        myClassFormat.setForeground(Qt.darkMagenta)
        pattern = QString("\\bMy[A-Za-z]+\\b")

        expression = QRegExp(pattern)
        index = text.indexOf(expression)
        while index >= 0:
            length = expression.matchedLength()
            setFormat(index, length, myClassFormat)
            index = text.indexOf(expression, index + length)

During cursor navigation in the associated editor, you can ask the current QTextBlock (retrieved using the block() function) if it has a user data object set and cast it to your BlockData object. Then you can check if the current cursor position matches with a previously recorded parenthesis position, and, depending on the type of parenthesis (opening or closing), find the next opening or closing parenthesis on the same level.

In this way you can do a visual parenthesis matching and highlight from the current cursor position to the matching parenthesis. That makes it easier to spot a missing parenthesis in your code and to find where a corresponding opening/closing parenthesis is when editing parenthesis intensive code.

PySide2.QtGui.QSyntaxHighlighter.setDocument(doc)
Parameters

docQTextDocument

Installs the syntax highlighter on the given QTextDocument doc . A QSyntaxHighlighter can only be used with one document at a time.

See also

document()

PySide2.QtGui.QSyntaxHighlighter.setFormat(start, count, color)
Parameters
  • startint

  • countint

  • colorQColor

PySide2.QtGui.QSyntaxHighlighter.setFormat(start, count, font)
Parameters
  • startint

  • countint

  • fontQFont

PySide2.QtGui.QSyntaxHighlighter.setFormat(start, count, format)
Parameters