全局名称'camera'未在python中定义

Question

在这个脚本中: -

camera_port = 0
ramp_frames = 400
camera = cv2.VideoCapture(camera_port) 
def get_image():
  global camera
  retval, im = camera.read()
  return im

def Camera():
    global camera
    for i in xrange(ramp_frames):
     temp = get_image()
    print("Taking image...")
    camera_capture = get_image()
    file = "opencv.png"
    cv2.imwrite(file, camera_capture)
    del(camera)

def Sendmail():
    loop_value = 1
    while loop_value==1:
        try:
            urllib2.urlopen("https://google.com")
        except urllib2.URLError, e:
            print "Network currently down." 
            sleep(20)
        else:
            print "Up and running." 
            loop_value = 0
def Email():
    loop_value = 2
    while loop_value==2:
        try:
            Camera()
            Sendmail()
            yag = yagmail.SMTP('email',   'pass')
            yag.send('amitaagarwal565@gmail.com', subject = "This is    opencv.png", contents = 'opencv.png')
            print "done"
        except smtplib.SMTPAuthenticationError:
            print 'Retrying in 30 seconds'
            sleep(30)
        else:
            print 'Sent!'
            sleep(20)
            loop_value = 2

我收到这个错误: -

我究竟做错了什么.我甚至在全球范围内定义了相机,即TWICE.可以somone请在代码中指出我的错误？我使用带有Opencv模块的python 2.7

File "C:\Python27\Scripts\Servers.py", line 22, in Camera
    temp = get_image()
  File "C:\Python27\Scripts\Servers.py", line 16, in get_image
    retval, im = camera.read()
NameError: global name 'camera' is not defined

更新 在上面查看更新的代码

Answer 1

您还需要camera在方法范围之外定义.该global关键字的作用是告诉Python您将修改您在外部定义的变量.如果还没有,则会出现此错误.

编辑

我没注意到你已经在camera外面宣布了.但是,您删除Camera()方法内的变量,当您尝试再次修改变量时,它具有几乎相同的效果.

编辑2

既然我可以看到你的代码真正做了什么以及你打算做什么,我认为你根本不应该使用全局camera,而是将其作为参数传递.这应该工作:

camera_port = 0
ramp_frames = 400

def get_image(camera):
    retval, im = camera.read()
    return im

def Camera(camera):
    for i in xrange(ramp_frames):
        temp = get_image(camera)
    print("Taking image...")
    camera_capture = get_image(camera)
    file = "opencv.png"
    cv2.imwrite(file, camera_capture)

def Sendmail():
    loop_value = 1
    while loop_value==1:
        try:
            urllib2.urlopen("https://google.com")
        except urllib2.URLError, e:
            print "Network currently down." 
            sleep(20)
        else:
            print "Up and running." 
            loop_value = 0

def Email():
    loop_value = 2
    while loop_value==2:
        try:
            camera = cv2.VideoCapture(camera_port) 
            Camera(camera)
            Sendmail()
            yag = yagmail.SMTP('email',   'pass')
            yag.send('amitaagarwal565@gmail.com', subject = "This is    opencv.png", contents = 'opencv.png')
            print "done"
        except smtplib.SMTPAuthenticationError:
            print 'Retrying in 30 seconds'
            sleep(30)
        else:
            print 'Sent!'
            sleep(20)
            loop_value = 2