问题
I have written a small GUI using PyQt4 that displays an image and gets point coordinates that the user clicks on. I need to display a 2D numpy array as a grayscale, so I am creating a QImage from the array, then from that creating a QPixmap. In Python 2 it works fine.
When I moved to Python 3, however, it can't decide on a constructor for QImage - it gives me the following error:
TypeError: arguments did not match any overloaded call:
QImage(): too many arguments
QImage(QSize, QImage.Format): argument 1 has unexpected type 'numpy.ndarray'
QImage(int, int, QImage.Format): argument 1 has unexpected type 'numpy.ndarray'
QImage(str, int, int, QImage.Format): argument 1 has unexpected type 'numpy.ndarray'
QImage(sip.voidptr, int, int, QImage.Format): argument 1 has unexpected type 'numpy.ndarray'
QImage(str, int, int, int, QImage.Format): argument 1 has unexpected type 'numpy.ndarray'
QImage(sip.voidptr, int, int, int, QImage.Format): argument 1 has unexpected type 'numpy.ndarray'
QImage(list-of-str): argument 1 has unexpected type 'numpy.ndarray'
QImage(str, str format=None): argument 1 has unexpected type 'numpy.ndarray'
QImage(QImage): argument 1 has unexpected type 'numpy.ndarray'
QImage(object): too many arguments
As far as I can tell, the QImage constructor I was calling previously was one of these:
QImage(str, int, int, QImage.Format)
QImage(sip.voidptr, int, int, QImage.Format)
I'm assuming that a numpy array fits one of the protocols necessary for one of these. I'm thinking it might have to do with an array versus a view, but all the variations I've tried either produce the above error or just make the GUI exit without doing anything. How can I reproduce the Python 2 behavior in Python 3?
The following is a small example, in which the same exact code works fine under Python 2 but not Python 3:
from __future__ import (print_function, division)
from PyQt4 import QtGui, QtCore
import numpy as np
class MouseView(QtGui.QGraphicsView):
mouseclick = QtCore.pyqtSignal(tuple)
def __init__(self, scene, parent=None):
super(MouseView, self).__init__(scene, parent=parent)
def mousePressEvent(self, event):
self.mouseclick.emit((event.x(),
self.scene().sceneRect().height() - event.y()))
class SimplePicker(QtGui.QDialog):
def __init__(self, data, parent=None):
super(SimplePicker, self).__init__(parent)
mind = data.min()
maxd = data.max()
bdata = ((data - mind) / (maxd - mind) * 255.).astype(np.uint8)
wdims = data.shape
wid = wdims[0]
hgt = wdims[1]
# This is the line of interest - it works fine under Python 2, but not Python 3
img = QtGui.QImage(bdata.T, wid, hgt,
QtGui.QImage.Format_Indexed8)
self.scene = QtGui.QGraphicsScene(0, 0, wid, hgt)
self.px = self.scene.addPixmap(QtGui.QPixmap.fromImage(img))
view = MouseView(self.scene)
view.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
view.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
view.setSizePolicy(QtGui.QSizePolicy.Fixed,
QtGui.QSizePolicy.Fixed)
view.setMinimumSize(wid, hgt)
view.mouseclick.connect(self.click_point)
quitb = QtGui.QPushButton("Done")
quitb.clicked.connect(self.quit)
lay = QtGui.QVBoxLayout()
lay.addWidget(view)
lay.addWidget(quitb)
self.setLayout(lay)
self.points = []
def click_point(self, xy):
self.points.append(xy)
def quit(self):
self.accept()
def test_picker():
x, y = np.mgrid[0:100, 0:100]
img = x * y
app = QtGui.QApplication.instance()
if app is None:
app = QtGui.QApplication(['python'])
picker = SimplePicker(img)
picker.show()
app.exec_()
print(picker.points)
if __name__ == "__main__":
test_picker()
I am using an Anaconda installation on Windows 7 64-bit, Qt 4.8.7, PyQt 4.10.4, numpy 1.9.2.
回答1:
In the PyQt constructor above, the following behavior is observed from a Numpy array called bdata
:
bdata
works correctly for both Python 2 and Python 3bdata.T
works for 2, not for 3 (constructor error)bdata.T.copy()
works for bothbdata[::-1,:]
does not work for either 2 or 3 (the same error)bdata[::-1,:].copy()
works for bothbdata[::-1,:].base
works for both, but loses the result of the reverse operation
As mentioned by @ekhumoro in the comments, you need something which supports the Python buffer protocol. The actual Qt constructor of interest here is this QImage constructor, or the const version of it:
QImage(uchar * data, int width, int height, Format format)
From the PyQt 4.10.4 documentation kept here, what PyQt expects for an unsigned char *
is different in Python 2 and 3:
Python 2:
If Qt expects a
char *
,signed char *
or anunsigned char *
(or a const version) then PyQt4 will accept a unicode or QString that contains only ASCII characters, a str, a QByteArray, or a Python object that implements the buffer protocol.
Python 3:
If Qt expects a
signed char *
or anunsigned char *
(or a const version) then PyQt4 will accept a bytes.
A Numpy array satisfies both of these, but apparently a Numpy view doesn't satisfy either. It's actually baffling that bdata.T
works at all in Python 2, as it purportedly returns a view:
>>> a = np.ones((2,3))
>>> b = a.T
>>> b.base is a
True
The final answer: If you need to do transformations that result in a view, you can avoid errors by doing a copy()
of the result to a new array for passing into the constructor. This may not be the best answer, but it will work.
来源:https://stackoverflow.com/questions/33445109/reproduce-python-2-pyqt4-qimage-constructor-behavior-in-python-3