Python syntax highlighting for QTextEdit C++/Qt

We were in need for some basic Python syntax highlighting in a QTextEdit box, and didn't immediately want to go fully pro with a Scintilla wrapper. (Update: We did that, too, in the end, according to this scintilla/qt post).

So we looked for a QSyntaxHighlighter subclass for Python formatting, but only found a PyQt example  which seems to be from Torsten Marek ( shlomme.diotavelli.net ) originally.

I asked Frankie to create a C++  Qt4 QSyntaxHighlighter class based on this, so here it is:

/*
$Id: PythonSyntaxHighlighter.cpp 167 2013-11-03 17:01:22Z oliver $
This is a C++ port of the following PyQt example
http://diotavelli.net/PyQtWiki/Python%20syntax%20highlighting
C++ port by Frankie Simon (www.kickdrive.de, www.fuh-edv.de)

The following free software license applies for this file ("X11 license"): 

Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
and associated documentation files (the "Software"), to deal in the Software without restriction, 
including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, 
and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, 
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial 
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT 
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN 
ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE 
USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#include "PythonSyntaxHighlighter.h"

PythonSyntaxHighlighter::PythonSyntaxHighlighter(QTextDocument *parent)
 : QSyntaxHighlighter(parent)
{
 keywords = QStringList() << "and" << "assert" << "break" << "class" << "continue" << "def" <<
        "del" << "elif" << "else" << "except" << "exec" << "finally" <<
        "for" << "from" << "global" << "if" << "import" << "in" <<
        "is" << "lambda" << "not" << "or" << "pass" << "print" <<
        "raise" << "return" << "try" << "while" << "yield" <<
        "None" << "True" << "False";
 
 operators = QStringList() << "=" <<
        // Comparison
        "==" << "!=" << "<" << "<=" << ">" << ">=" <<
        // Arithmetic
        "\\+" << "-" << "\\*" << "/" << "//" << "%" << "\\*\\*" <<
        // In-place
        "\\+=" << "-=" << "\\*=" << "/=" << "%=" <<
        // Bitwise
        "\\^" << "\\|" << "&" << "~" << ">>" << "<<";

 braces = QStringList() << "{" << "}" << "\\(" << "\\)" << "\\[" << "]";

 basicStyles.insert("keyword", getTextCharFormat("blue"));
 basicStyles.insert("operator", getTextCharFormat("red"));
 basicStyles.insert("brace", getTextCharFormat("darkGray"));
    basicStyles.insert("defclass", getTextCharFormat("black", "bold"));
 basicStyles.insert("brace", getTextCharFormat("darkGray"));
 basicStyles.insert("string", getTextCharFormat("magenta"));
 basicStyles.insert("string2", getTextCharFormat("darkMagenta"));
 basicStyles.insert("comment", getTextCharFormat("darkGreen", "italic"));
 basicStyles.insert("self", getTextCharFormat("black", "italic"));
 basicStyles.insert("numbers", getTextCharFormat("brown"));

 triSingleQuote.setPattern("'''");
 triDoubleQuote.setPattern("\"\"\"");

 initializeRules();
}

void PythonSyntaxHighlighter::initializeRules()
{
 foreach (QString currKeyword, keywords)
 {
  rules.append(HighlightingRule(QString("\\b%1\\b").arg(currKeyword), 0, basicStyles.value("keyword")));
 }
 foreach (QString currOperator, operators)
 {
  rules.append(HighlightingRule(QString("%1").arg(currOperator), 0, basicStyles.value("operator")));
 }
 foreach (QString currBrace, braces)
 {
  rules.append(HighlightingRule(QString("%1").arg(currBrace), 0, basicStyles.value("brace")));
 }
 // 'self'
    rules.append(HighlightingRule("\\bself\\b", 0, basicStyles.value("self")));

    // Double-quoted string, possibly containing escape sequences
 // FF: originally in python : r'"[^"\\]*(\\.[^"\\]*)*"'
    rules.append(HighlightingRule("\"[^\"\\\\]*(\\\\.[^\"\\\\]*)*\"", 0, basicStyles.value("string")));
    // Single-quoted string, possibly containing escape sequences
 // FF: originally in python : r"'[^'\\]*(\\.[^'\\]*)*'"
 rules.append(HighlightingRule("'[^'\\\\]*(\\\\.[^'\\\\]*)*'", 0, basicStyles.value("string")));

    // 'def' followed by an identifier
 // FF: originally: r'\bdef\b\s*(\w+)'
    rules.append(HighlightingRule("\\bdef\\b\\s*(\\w+)", 1, basicStyles.value("defclass")));
    //  'class' followed by an identifier
 // FF: originally: r'\bclass\b\s*(\w+)'
 rules.append(HighlightingRule("\\bclass\\b\\s*(\\w+)", 1, basicStyles.value("defclass")));

    // From '#' until a newline
 // FF: originally: r'#[^\\n]*'
    rules.append(HighlightingRule("#[^\\n]*", 0, basicStyles.value("comment")));

    // Numeric literals
    rules.append(HighlightingRule("\\b[+-]?[0-9]+[lL]?\\b", 0, basicStyles.value("numbers"))); // r'\b[+-]?[0-9]+[lL]?\b'
    rules.append(HighlightingRule("\\b[+-]?0[xX][0-9A-Fa-f]+[lL]?\\b", 0, basicStyles.value("numbers"))); // r'\b[+-]?0[xX][0-9A-Fa-f]+[lL]?\b'
    rules.append(HighlightingRule("\\b[+-]?[0-9]+(?:\\.[0-9]+)?(?:[eE][+-]?[0-9]+)?\\b", 0, basicStyles.value("numbers"))); // r'\b[+-]?[0-9]+(?:\.[0-9]+)?(?:[eE][+-]?[0-9]+)?\b'
}

void PythonSyntaxHighlighter::highlightBlock(const QString &text)
{ 
 foreach (HighlightingRule currRule, rules)
 {
  int idx = currRule.pattern.indexIn(text, 0);
  while (idx >= 0)
  {
   // Get index of Nth match
   idx = currRule.pattern.pos(currRule.nth);
   int length = currRule.pattern.cap(currRule.nth).length();
   setFormat(idx, length, currRule.format);
   idx = currRule.pattern.indexIn(text, idx + length);
  }
 }
    
 setCurrentBlockState(0);

    // Do multi-line strings
    bool isInMultilne = matchMultiline(text, triSingleQuote, 1, basicStyles.value("string2"));
    if (!isInMultilne)
  isInMultilne = matchMultiline(text, triDoubleQuote, 2, basicStyles.value("string2"));
}

bool PythonSyntaxHighlighter::matchMultiline(const QString &text, const QRegExp &delimiter, const int inState, const QTextCharFormat &style)
{
    int start = -1;
 int add = -1;
 int end = -1;
 int length = 0;

 // If inside triple-single quotes, start at 0
 if (previousBlockState() == inState) {
        start = 0;
        add = 0;
 }
 // Otherwise, look for the delimiter on this line
 else { 
        start = delimiter.indexIn(text);
        // Move past this match
        add = delimiter.matchedLength();
 }

    // As long as there's a delimiter match on this line...
    while (start >= 0) {
        // Look for the ending delimiter
        end = delimiter.indexIn(text, start + add);
        // Ending delimiter on this line?
        if (end >= add) {
            length = end - start + add + delimiter.matchedLength();
            setCurrentBlockState(0);
  }
        // No; multi-line string
        else {
            setCurrentBlockState(inState);
            length = text.length() - start + add;
  }
        // Apply formatting and look for next
        setFormat(start, length, style);        
        start = delimiter.indexIn(text, start + length);
 }
    // Return True if still inside a multi-line string, False otherwise
    if (currentBlockState() == inState)
        return true;
    else
        return false;
}

const QTextCharFormat PythonSyntaxHighlighter::getTextCharFormat(const QString &colorName, const QString &style)
{
 QTextCharFormat charFormat;
 QColor color(colorName);
 charFormat.setForeground(color);
 if (style.contains("bold", Qt::CaseInsensitive))
  charFormat.setFontWeight(QFont::Bold);
 if (style.contains("italic", Qt::CaseInsensitive))
  charFormat.setFontItalic(true);
 return charFormat;
}

$Id: KickPythonSyntaxHighlighter.h 167 2013-11-03 17:01:22Z oliver $
This is a C++ port of the following PyQt example
http://diotavelli.net/PyQtWiki/Python%20syntax%20highlighting
C++ port by Frankie Simon (docklight.de, www.fuh-edv.de)

The following free software license applies for this file ("X11 license"): 

Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
and associated documentation files (the "Software"), to deal in the Software without restriction, 
including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, 
and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, 
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial 
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT 
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN 
ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE 
USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#ifndef KICKPYTHONSYNTAXHIGHLIGHTER_H
#define KICKPYTHONSYNTAXHIGHLIGHTER_H




#include <QSyntaxHighlighter>

//! Container to describe a highlighting rule. Based on a regular expression, a relevant match # and the format.
class HighlightingRule
{
public: 
 HighlightingRule(const QString &patternStr, int n, const QTextCharFormat &matchingFormat)
 {
  originalRuleStr = patternStr;
  pattern = QRegExp(patternStr);
  nth = n;
  format = matchingFormat;
 } 
 QString originalRuleStr;
 QRegExp pattern;
 int nth;
 QTextCharFormat format;
};

//! Implementation of highlighting for Python code.
class KickPythonSyntaxHighlighter : public QSyntaxHighlighter
{
 Q_OBJECT
public:
 KickPythonSyntaxHighlighter(QTextDocument *parent = 0);
protected:
     void highlightBlock(const QString &text);
private:
 QStringList keywords;
 QStringList operators;
 QStringList braces;

 QHash<QString, QTextCharFormat> basicStyles;
 
 void initializeRules();
 
 //! Highlighst multi-line strings, returns true if after processing we are still within the multi-line section.
 bool matchMultiline(const QString &text, const QRegExp &delimiter, const int inState, const QTextCharFormat &style);
 const QTextCharFormat getTextCharFormat(const QString &colorName, const QString &style = QString());

 QList<HighlightingRule> rules;
 QRegExp triSingleQuote;
 QRegExp triDoubleQuote;
};

#endif

Using a QSyntaxHighlighter for QTextEdit is a one-liner, e.g.


PythonSyntaxHighlighter *pythonHighlighter = new PythonSyntaxHighlighter(ui.plainTextEditScript->document());