python - Resizing QPixmap while maintaining aspect ratio -

to keep aspect ratio of image fixed while resizing qdialog i've tried following:

import os, sys pyqt5.qtwidgets import qapplication, qdialog, qgridlayout, qlabel pyqt5.qtgui import qpixmap pyqt5.qtcore import qt  class dialog(qdialog):     def __init__(self, parent=none):         super(dialog, self).__init__(parent)         self.pic = qlabel()         self.pic.resizeevent = onresize          self.pic.setpixmap(qpixmap(os.getcwd() + "/images/1.jpg").scaled(300, 200, qt.keepaspectratio,qt.smoothtransformation))         layout = qgridlayout()         layout.addwidget(self.pic, 1, 0)         self.setlayout(layout)  def onresize(event):     size = dialog.pic.size()     dialog.pic.setpixmap(qpixmap(os.getcwd() + "/images/1.jpg").scaled(size, qt.keepaspectratio, qt.smoothtransformation))      if __name__ == '__main__':     app = qapplication(sys.argv)     dialog = dialog()     dialog.show()     sys.exit(app.exec_()) 

as espected image starts 300x200. can enlarged wished size can't reduced @ (down 300x200 after enlargement). onresize seems lack something.

i have working example problem. don't use setpixmap method draw pixmap on widget, draw reimplementing paintevent of widget.

from pyqt4 import qtgui, qtcore import sys pyqt4.qtcore import qt  class label(qtgui.qlabel):     def __init__(self, img):         super(label, self).__init__()         self.setframestyle(qtgui.qframe.styledpanel)         self.pixmap = qtgui.qpixmap(img)      def paintevent(self, event):         size = self.size()         painter = qtgui.qpainter(self)         point = qtcore.qpoint(0,0)         scaledpix = self.pixmap.scaled(size, qt.keepaspectratio, transformmode = qt.smoothtransformation)         # start painting label left upper corner         point.setx((size.width() - scaledpix.width())/2)         point.sety((size.height() - scaledpix.height())/2)         print point.x(), ' ', point.y()         painter.drawpixmap(point, scaledpix)   class main(qtgui.qwidget):               def __init__(self):         super(main, self).__init__()         layout = qtgui.qgridlayout()         label = label(r"/path/to/some/image.png")         layout.addwidget(label)         layout.setrowstretch(0,1)         layout.setcolumnstretch(0,1)          self.setlayout(layout)         self.show()  if __name__ =="__main__":     app = qtgui.qapplication(sys.argv)     widget = main()     sys.exit(app.exec_()) 

copy whole code , run is. try scale window appears. understand paintevent in label class. dont forget change path existing png image in __init__ of main class.

update changing image:

to change image can add method changepixmap(self, img) label class , call on event on want change pixmap.

... def changepixmap(self, img):     self.pixmap = qtgui.qpixmap(img)     self.repaint() # repaint() trigger paintevent(self, event), way new pixmap drawn on label 

you can call method main class saving reference label class in member variable.

... self.label = label('/path/to/image.png') ... 

then inside event in main class, call self.label.changepixmap('path/to/new/image.png')