python和全局變量

如何正確設置全局變量？python和全局變量

# default objects is being set as None (null), after importing the piCamera library 
camera = None

之後，我宣佈攝像頭類的GET定義：

class Webcam: 
    def GET(self): 
     web.header('Content-type','multipart/x-mixed-replace; boundary=--jpgboundary') 
     stream=io.BytesIO() 
     start=time.time() 

     for foo in camera.capture_continuous(stream,'jpeg'): 
      web.header('Content-type','--jpgboundary') 
      web.header('Content-type','image/jpeg') 
      web.header('Content-length',len(stream.getvalue())) 
      yield (stream.getvalue()) 
      stream.seek(0) 
      stream.truncate() 
      time.sleep(.5) 


if __name__ == "__main__": 
    camera = picamera.PiCamera() 
    global camera 
    camera.resolution = (640, 480) 
    app = web.application(urls, globals()) 
    app.internalerror = web.debugerror 
    app.run()

我應該把if __name__ == "__main__":我定義了網絡攝像頭前級？

這裏是我的電話追蹤：

Traceback (most recent call last): 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/wsgiserver/__init__.py", line 1245, in communicate 
    req.respond() 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/wsgiserver/__init__.py", line 775, in respond 
    self.server.gateway(self).respond() 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/wsgiserver/__init__.py", line 2018, in respond 
    response = self.req.server.wsgi_app(self.env, self.start_response) 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/httpserver.py", line 306, in __call__ 
    return self.app(environ, xstart_response) 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/httpserver.py", line 274, in __call__ 
    return self.app(environ, start_response) 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/application.py", line 281, in wsgi 
    result = peep(result) 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/application.py", line 261, in peep 
    firstchunk = iterator.next() 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/application.py", line 605, in wrap 
    yield next() 
    File "/usr/local/lib/python2.7/dist-packages/web.py-0.37-py2.7.egg/web/application.py", line 597, in next 
    return result.next() 
    File "/home/pi/piApp/index.py", line 77, in GET 
    for foo in camera.capture_continuous(stream,'jpeg'): 
AttributeError: 'NoneType' object has no attribute 'capture_continuous'

來源

2014-07-13 el.severo

全球關鍵字只讓你分配到模塊中的全局範圍較小。它在這裏什麼都不做，因爲如果語句不創建範圍。 – geoffspear

@Wooble：你能否建議我另一種選擇？問題是我想從不同的課程中訪問相機。 –

看起來你正在運行這是一個庫文件，因此__main__部分不執行。將該代碼放在全局範圍內。

我猜這樣的事情是你想要什麼：

def main(): 
    global camera 
    camera = picamera.PiCamera() 
    camera.resolution = (640, 480) 
    app = web.application(urls, globals()) 
    app.internalerror = web.debugerror 
    app.run() 

main()

來源

2014-07-13 16:25:46 hughdbrown

確保您有V4L驅動程序，試試這個：

sudo modprobe bcm2835-v4l2

來源

2016-10-13 08:16:30

python和全局變量

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