Python et variables globales

Question

Comment configurer correctement la variable globale?

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

après que je déclare la classe Webcam avec la GET définition:

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() 

Dois-je mettre le if __name__ == "__main__": avant que je sois la définition de la classe Webcam?

Voici mon retraçage des appels:

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' 

Answer 1

Il semble que vous utilisez cela comme un fichier de bibliothèque et donc la section __main__ n'exécute pas. Mettez ce code à portée globale.

Je suppose que quelque chose comme ceci est ce que vous voulez:

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

main() 

Answer 2

Assurez-vous que vous avez les pilotes V4l, essayez ceci:

sudo modprobe bcm2835-v4l2