Qt re-sizable image label.

qimage_label.py

from qtpy import QtCore, QtWidgets, QtGui


class QImageLabel(QtWidgets.QLabel):
    doubleClicked = QtCore.Signal()

    def loadFile(self, filename):
        """Load the image with the given filename."""
        pm = QtGui.QPixmap()
        with open(filename, 'rb') as f:
            pm.loadFromData(f.read())
        self.setPixmap(pm)

    def setPixmap(self, pixmap):
        """Set the pixmap to display the image for."""
        self._pixmap = pixmap
        super().setPixmap(pixmap)

    def pixmapSize(self):
        """Get the pixmap size."""
        try:
            return self._pixmap.size()
        except:
            return self.size()

    def toggleMaximized(self):
        """Toggle the image as maximized or the normal image size."""
        if self.isMaximized():
            self.showNormal()
            self.resize(self.pixmapSize())
        else:
            self.showMaximized()

    def mouseDoubleClickEvent(self, event):
        self.doubleClicked.emit()
        return super().mouseDoubleClickEvent(event)

    def resizeEvent(self, event):
        try:
            size = event.size()
            if size != super().pixmap().size():
                super().setPixmap(self._pixmap.scaled(size.width(), size.height(),
                                                      QtCore.Qt.KeepAspectRatio,
                                                      QtCore.Qt.SmoothTransformation))
        except (AttributeError, Exception):
            pass
        return super().resizeEvent(event)


if __name__ == '__main__':
    import sys

    FILENAME = None
    if len(sys.argv) > 1:
        FILENAME = sys.argv[1]

    app = QtWidgets.QApplication([])

    lbl = QClickImgLabel()
    lbl.loadFile(FILENAME)
    lbl.show()
    lbl.doubleClicked.connect(lbl.toggleMaximized)

    app.exec_()