python - Oct2Py 使用返回多个参数的 Psychtoolbox 函数给出“TypeError: cannot unpack non-iterable float object”

Question

我正在使用 Oct2py 包从他们的站点运行一个非常基本的 Psychtoolbox 示例，当我尝试返回两个浮点值时，我遇到了一个问题，它看起来像：

from oct2py import octave
import sys

def ptb():
    # Clear the workspace and the screen
    octave.sca;
    octave.close;

    octave.PsychDebugWindowConfiguration; 

    # Here we call some default settings for setting up Psychtoolbox
    octave.PsychDefaultSetup(2);

    # Get the screen numbers. This gives us a number for each of the screens
    # attached to our computer.
    screens = octave.Screen('Screens');

    # To draw we select the maximum of these numbers. So in a situation where we
    # have two screens attached to our monitor we will draw to the external
    # screen.
    screenNumber = octave.max(screens);

    # Define black and white (white will be 1 and black 0). This is because
    # in general luminace values are defined between 0 and 1 with 255 steps in
    # between. All values in Psychtoolbox are defined between 0 and 1
    white = octave.WhiteIndex(screenNumber);
    black = octave.BlackIndex(screenNumber);

    # Do a simply calculation to calculate the luminance value for grey. This
    # will be half the luminace values for white
    grey = white / 2;

    # Open an on screen window using PsychImaging and color it grey.
    window, windowRect = octave.PsychImaging('OpenWindow', screenNumber, grey);

    # Now we have drawn to the screen we wait for a keyboard button press (any
    # key) to terminate the demo.
    octave.KbStrokeWait;

    # Clear the screen.
    octave.sca;
    
    sys.exit()
    
if __name__ == "__main__":
    ptb()

错误发生在第 49 行：

TypeError                                 Traceback (most recent call last)
<ipython-input-1-6e0dcd049170> in <module>
     47 
     48 if __name__ == "__main__":
---> 49     ptb()

<ipython-input-1-6e0dcd049170> in ptb()
     37 
     38     #Open an on screen window using PsychImaging and color it grey.
---> 39     window, windowRect = octave.PsychImaging('OpenWindow', screenNumber, grey);
     40 
     41     #Now we have drawn to the screen we wait for a keyboard button press (any

TypeError: cannot unpack non-iterable float object

我在网上寻找这个错误的帮助，但我看到的解释很少，没有一个能帮助我。当我在 Octave 中执行它时，它运行良好，但在 Python 中我遇到了这个问题，我试图在 window 和 windowRect 之间放置括号，但它也不起作用。我怎么能继续呢？

标签： pythonoctavepsychtoolboxoct2py

Answer 1

将评论转换为答案。

这里的问题是，当 oct2py 运行该行时，它的行为就像使用单个参数调用函数一样。Oct2py 无法从 python 调用的输出数量推断参数的数量。（显然这曾经是旧 oct2py 版本的情况，但不再是：请参阅此答案）。

正如链接的答案所暗示的那样，这样做的方法是nout=2向函数传递一个额外的参数。即你的电话（假设所有其他参数都是正确的？）应该是：

window, windowRect = octave.PsychImaging('OpenWindow', screenNumber, grey, nout=2);

或者，您可以使用“eval”以更自然的八度语法运行您的函数，即

octave.eval("[window, windowRect] = PsychImaging('OpenWindow', screenNumber, grey);")

我注意到，在这种情况下，您实际上并不需要使用生成的输出变量，但如果您这样做了，您可以使用 oct2py 的pull函数将它们检索到您的 python 会话中。