Add code syntax highlight utils (#88)

* add code syntax highlight code

* add example

* add documentation and fix example

* add tests

* add information about napari theme usage

* clean napari mention

docs/utils.md

@@ -0,0 +1,10 @@
+# Utils
+
+## Code highlighting
+
+`superqt` provides a code highlighter subclass of `QSyntaxHighlighter`
+that can be used to highlight code in a QTextEdit.
+
+Code lexer and available styles are from [`pygments`](https://pygments.org/) python library
+List of available languages are available [here](https://pygments.org/languages/).
+List of available styles are available [here](https://pygments.org/styles/).

examples/code_highlight.py

@@ -0,0 +1,32 @@
+from PyQt5.QtGui import QColor, QPalette
+from qtpy.QtWidgets import QApplication, QTextEdit
+
+from superqt.utils import CodeSyntaxHighlight
+
+app = QApplication([])
+
+text_area = QTextEdit()
+
+highlight = CodeSyntaxHighlight(text_area.document(), "python", "monokai")
+
+palette = text_area.palette()
+palette.setColor(QPalette.Base, QColor(highlight.background_color))
+text_area.setPalette(palette)
+text_area.setText(
+    """from argparse import ArgumentParser
+
+def main():
+    parser = ArgumentParser()
+    parser.add_argument("name", help="Your name")
+    args = parser.parse_args()
+    print(f"Hello {args.name}")
+
+
+if __name__ == "__main__":
+    main()
+"""
+)
+
+text_area.show()
+
+app.exec_()

setup.cfg

@@ -36,6 +36,7 @@ project_urls =
 packages = find:
 install_requires =
     packaging
+    pygments>=2.4.0
     qtpy>=1.1.0
     typing-extensions>=3.10.0.0
 python_requires = >=3.7

src/superqt/utils/__init__.py

@@ -1,4 +1,5 @@
 __all__ = (
+    "CodeSyntaxHighlight",
     "create_worker",
     "ensure_main_thread",
     "ensure_object_thread",
@@ -15,7 +16,7 @@ __all__ = (
     "WorkerBase",
 )
 
-
+from ._code_syntax_highlight import CodeSyntaxHighlight
 from ._ensure_thread import ensure_main_thread, ensure_object_thread
 from ._message_handler import QMessageHandler
 from ._misc import signals_blocked

src/superqt/utils/_code_syntax_highlight.py

@@ -0,0 +1,93 @@
+from itertools import takewhile
+
+from pygments import highlight
+from pygments.formatter import Formatter
+from pygments.lexers import find_lexer_class, get_lexer_by_name
+from pygments.util import ClassNotFound
+from qtpy import QtGui
+
+# inspired by  https://github.com/Vector35/snippets/blob/master/QCodeEditor.py (MIT license) and
+# https://pygments.org/docs/formatterdevelopment/#html-3-2-formatter
+
+
+def get_text_char_format(style):
+    """
+    Return a QTextCharFormat with the given attributes.
+
+    https://pygments.org/docs/formatterdevelopment/#html-3-2-formatter
+    """
+
+    text_char_format = QtGui.QTextCharFormat()
+    text_char_format.setFontFamily("monospace")
+    if style.get("color"):
+        text_char_format.setForeground(QtGui.QColor(f"#{style['color']}"))
+
+    if style.get("bgcolor"):
+        text_char_format.setBackground(QtGui.QColor(style["bgcolor"]))
+
+    if style.get("bold"):
+        text_char_format.setFontWeight(QtGui.QFont.Bold)
+    if style.get("italic"):
+        text_char_format.setFontItalic(True)
+    if style.get("underline"):
+        text_char_format.setFontUnderline(True)
+
+    # TODO find if it is possible to support border style.
+
+    return text_char_format
+
+
+class QFormatter(Formatter):
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
+        self.data = []
+        self._style = {name: get_text_char_format(style) for name, style in self.style}
+
+    def format(self, tokensource, outfile):
+        """
+        `outfile` is argument from parent class, but
+        in Qt we do not produce string output, but QTextCharFormat, so it needs to be
+        collected using `self.data`.
+        """
+        self.data = []
+
+        for token, value in tokensource:
+            self.data.extend(
+                [
+                    self._style[token],
+                ]
+                * len(value)
+            )
+
+
+class CodeSyntaxHighlight(QtGui.QSyntaxHighlighter):
+    def __init__(self, parent, lang, theme):
+        super().__init__(parent)
+        self.formatter = QFormatter(style=theme)
+        try:
+            self.lexer = get_lexer_by_name(lang)
+        except ClassNotFound:
+            self.lexer = find_lexer_class(lang)()
+
+    @property
+    def background_color(self):
+        return self.formatter.style.background_color
+
+    def highlightBlock(self, text):
+        cb = self.currentBlock()
+        p = cb.position()
+        text_ = self.document().toPlainText() + "\n"
+        highlight(text_, self.lexer, self.formatter)
+
+        enters = sum(1 for _ in takewhile(lambda x: x == "\n", text_))
+        # pygments lexer ignore leading empty lines, so we need to do correction
+        # here calculating the number of empty lines.
+
+        # dirty, dirty hack
+        # The core problem is that pygemnts by default use string streams,
+        # that will not handle QTextCharFormat, so wee need use `data` property to work around this.
+        for i in range(len(text)):
+            try:
+                self.setFormat(i, 1, self.formatter.data[p + i - enters])
+            except IndexError:  # pragma: no cover
+                pass

tests/test_code_highlight.py

@@ -0,0 +1,19 @@
+from qtpy.QtWidgets import QTextEdit
+
+from superqt.utils import CodeSyntaxHighlight
+
+
+def test_code_highlight(qtbot):
+    widget = QTextEdit()
+    qtbot.addWidget(widget)
+    code_highlight = CodeSyntaxHighlight(widget, "python", "default")
+    assert code_highlight.background_color == "#f8f8f8"
+    widget.setText("from argparse import ArgumentParser")
+
+
+def test_code_highlight_by_name(qtbot):
+    widget = QTextEdit()
+    qtbot.addWidget(widget)
+    code_highlight = CodeSyntaxHighlight(widget, "Python Traceback", "monokai")
+    assert code_highlight.background_color == "#272822"
+    widget.setText("from argparse import ArgumentParser")