fix(plot_renderer): list image formats properly in the export dialog

The image filter of the file dialog shown by QwtPlotRenderer.exportTo read
"Images (*.b'bmp' *.b'png' ...)": the image format names returned by
QImageWriter.supportedImageFormats() are QByteArray objects, which were
converted with str() instead of being decoded.

- Decode the format names (bytes(fmt).decode(), supported by PyQt5, PyQt6
  and PySide6).
- Regression test: file dialog replaced by a stub capturing the filters,
  image filter equal to the decoded format names.
- Changelog entry.

The export itself (QwtPlotRenderer.renderDocument) is not affected: PNG,
SVG and PDF exports already work with the three Qt bindings.

Refs #115

Assisted-by: Claude Opus 5.5

Author: PierreRaybaut

CHANGELOG.md

@@ -18,6 +18,7 @@
 - Fixed the `QwtPainterCommand` copy constructor (`QwtPainterCommand(other)`), which raised an `AttributeError` for state commands and a `TypeError` (Qt objects cannot be pickled) for pixmap and image commands: commands of every type can now be copied, the copy being independent of the original ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 - Fixed `QwtDynGridLayout` (used by `QwtLegend`), whose `numRows()` returned a float (e.g. `2.5` for 3 items on 2 columns) and which raised a `TypeError` when laying out its items with vertical expansion (`setExpandingDirections(Qt.Vertical)`) ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 - Fixed canvas style sheets with rounded borders (e.g. `plot.canvas().setStyleSheet("border: 2px solid black; border-radius: 8px;")`), which raised a `TypeError` on each style change, resize and paint event (aborting the process with PyQt's default exception hook): the rounded border of the style sheet is now taken into account to clip the plot items and to fill the corners with the background of the parent widget, as in Qwt ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
+- Fixed the image formats listed by the file dialog of `QwtPlotRenderer.exportTo`, which read `*.b'bmp' *.b'png' ...` instead of `*.bmp *.png ...` ([Issue #115](https://github.com/PlotPyStack/PythonQwt/issues/115))
 
 ## Version 0.16.3
 

qwt/plot_renderer.py

@@ -722,7 +722,7 @@ def exportTo(self, plot, documentname, sizeMM=None, resolution=85):
             for idx, fmt in enumerate(imageFormats):
                 if idx > 0:
                     imageFilter += " "
-                imageFilter += "*." + str(fmt)
+                imageFilter += "*." + bytes(fmt).decode()
             imageFilter += ")"
             filter_ += [imageFilter]
         filename, _s = getsavefilename(

qwt/tests/test_issue115_porting_bugs.py

@@ -21,6 +21,7 @@
 from qtpy import QtGui as QG
 from qtpy import QtWidgets as QW
 
+import qwt.plot_renderer
 from qwt import (
     QwtLegend,
     QwtLinearScaleEngine,
@@ -635,6 +636,33 @@ def test_canvas_rounded_style_sheet(style_sheet, backing_store):
     del app
 
 
+# ---------------------------------------------------------------------------
+# QwtPlotRenderer.exportTo
+# ---------------------------------------------------------------------------
+
+
+def test_renderer_export_to_image_filter(monkeypatch):
+    """The file dialog of exportTo lists the image formats properly"""
+    app = _ensure_app()  # keep a reference alive for the duration of the test
+    captured = []
+
+    def fake_getsavefilename(*args, **kwargs):
+        captured.append(args[3])  # filters
+        return "", ""  # dialog canceled
+
+    monkeypatch.setattr(qwt.plot_renderer, "getsavefilename", fake_getsavefilename)
+    plot = QwtPlot()
+    assert QwtPlotRenderer().exportTo(plot, "plot") is False
+    filters = captured[0].split(";;")
+    formats = QG.QImageWriter.supportedImageFormats()
+    expected = " ".join("*." + bytes(fmt).decode() for fmt in formats)
+    assert filters[-1] == f"Images ({expected})"
+    assert "*.png" in filters[-1].split()
+    assert "b'" not in captured[0]
+    plot.close()
+    del app
+
+
 if __name__ == "__main__":
     for name in ("toPixmap", "toImage"):
         test_graphic_conversion_default_size(name)