Create a pixmap:
pixmap = QtGui.QPixmap(path)
and then use QPixmap.scaledToWidth or QPixmap.scaledToHeight:
pixmap2 = pixmap.scaledToWidth(64)
pixmap3 = pixmap.scaledToHeight(64)
With a 2048×1024 image, the first method would result in an image that is 64×32, whilst the second would be 128×64. Obviously it is impossible to resize a 2048×1024 image to 64×64 whilst keeping the same aspect ratio (because the ratios are different).
To avoid choosing between width or height, you can use QPixmap.scaled:
pixmap4 = pixmap.scaled(64, 64, QtCore.Qt.KeepAspectRatio)
which will automatically adjust to the largest size possible.
To resize the image to an exact size, do:
pixmap5 = pixmap.scaled(64, 64)
Of course, in this case, the resulting image won’t keep the same aspect ratio, unless the original image was also 1:1.