Question

全局上下文中使用的全局键盘在python中意味着什么？我知道如果在函数内部使用它，它可以让你修改全局变量，但是当你使用global声明一个全局变量时我不知道它是如何工作的，因为我认为当你在函数之外声明它们时它们已经是全局变量了。如下面的代码所示：

from ctypes import *

import ctypes

import os
import cv2
import time
import Image
import argparse
import numpy as np
import thread as thread

from select import select
from evdev import InputDevice

import ArducamSDK

COLOR_BYTE2RGB = 49
CAMERA_MT9F002 = 0x4D091031
SensorShipAddr = 32
I2C_MODE_16_16  = 3
usbVid = 0x52cb
Width = 4384
Height = 3288
cfg ={"u32CameraType":CAMERA_MT9F002,
      "u32Width":Width,"u32Height":Height,
      "u32UsbVersion":1,
      "u8PixelBytes":1,
      "u16Vid":0x52cb,
      "u8PixelBits":8,
      "u32SensorShipAddr":SensorShipAddr,
      "emI2cMode":I2C_MODE_16_16 }
# *********** Here is where I'm talking about****************
global saveNum,saveFlag,downFlag,flag,handle,openFlag
openFlag = False
saveNum = 0
handle = {}
downFlag = False
flag = True
saveFlag = False


regArr= [[0x301A, 0x0018],

    [0x0103, 0x1   ],  

    [0x31AE, 0x301 ],  
    [0x0112, 0x0C0C],   
    [0x301A, 0x0010],   
    [0x3064, 0x0805],   
    [0x301E, 0x00A8],   
    [0x301A, 0x10DC],   
    [0x0104, 0x1   ],  
    [0x0100, 0x0   ],  

    [0x0300, 0x4   ],  
    [0x0302, 0x01  ],  
    [0x0304, 0x03  ],  
    [0x0306, 0x6E  ],  
    [0x0308, 0x0C  ],  
    [0x030A, 0x01  ],  

    [0x3016, 0x111 ],  
    [0x0344, 0x090 ],  
    [0x0348, 0x11AF],   
    [0x0346, 0x020 ],  
    [0x034A, 0xCF7 ],  
    [0x3040, 0x0041],   
    [0x0400, 0x0   ],  
    [0x0404, 0x10  ],  
    [0x034C, 0x1120],   
    [0x034E, 0xCD8 ],  
    [0x0342, 0x33C1],   
    [0x0340, 0x0D67],   
    [0x3010, 0x00CF],   
    [0x3012, 0x0010],   
    [0x3014, 0x1F50],   
    [0x3018, 0x0000],   

    [0x0104, 0x0],  
    [0x0100, 0x1],  
    [0x0304, 8],

    [0x301a, 0x5ccc],        
    [0x3012, 500],
    [0x0206, 33],
    [0x0208, 50],
    [0x020a, 50],
    [0x020c, 33],

    [0xffff, 0xffff],
    [0xffff, 0xffff]
]


ap = argparse.ArgumentParser()
ap.add_argument("--type",default = "jpg",required = False, help = "type to the image file")
ap.add_argument("--name",required = False, help = "name to the image file")
args = vars(ap.parse_args())

def readThread(threadName,read_Flag):
    global flag,handle
    data = {}
    cv2.namedWindow("MT9F002",1)
    while flag:
        if ArducamSDK.Py_ArduCam_availiable(handle) > 0:

            res,data = ArducamSDK.Py_ArduCam_read(handle,Width * Height)
            if res == 0:
                ArducamSDK.Py_ArduCam_del(handle)
            else:
                print "read data fail!"

        else:
            print "is not availiable"
        if len(data) >= Width * Height:
            show(data)
            flag = False
        else:
            print "data length is not enough!"
        if flag == False:       
            break

thread.start_new_thread( readThread,("Thread-2", flag,))

pass

def show(bufferData):
    global downFlag,saveFlag,saveNum
    image = Image.frombuffer("L",(Width,Height),bufferData)
    img = np.array(image)
    height,width = img.shape[:2]
    img2 = cv2.cvtColor(img,COLOR_BYTE2RGB)
        saveNum += 1

    if args["name"] != "":
                name = args["name"]   
        else:
                name = str(saveNum)
    if "bmp" == args["type"]:        
                name += ".bmp"
        if "png" == args["type"]:        
                name += ".png"
        if "jpg" == args["type"]:        
                name += ".jpg"
    cv2.imwrite(name,img2)  


def video():
    global flag,regArr,handle
    regNum = 0
    res,handle = ArducamSDK.Py_ArduCam_autoopen(cfg)
    capFlag = True
    if res == 0:
        openFlag = True
        print "device open success!"
        while (regArr[regNum][0] != 0xFFFF):
            ArducamSDK.Py_ArduCam_writeSensorReg(handle,regArr[regNum][0],regArr[regNum][1])
            regNum = regNum + 1
        res = ArducamSDK.Py_ArduCam_beginCapture(handle)

        if res == 0:
            print "transfer task create success!"
            while flag :
                                if capFlag:
                                        res = ArducamSDK.Py_ArduCam_capture(handle)
                                        if res != 0:
                                                print "capture fail!"
                                                break
                                        else:
                                                capFlag = False
                                time.sleep(0.4)
                if flag == False:       
                    break
        else:
            print "transfer task create fail!"
        res = ArducamSDK.Py_ArduCam_close(handle)
        if res == 0:
            openFlag = False
            print "device close success!"
        else:
            print "device close fail!"
    else:
        print "device open fail!"

if __name__ == "__main__":      
    video()

Answer 1

Absobleepinglululy什么都没有。 global是编译器的一个提示，它需要检查当前作用域内代码名称的外部作用域。由于全球范围是最外层的范围，因此没有效果。

>>> import dis
>>> def foo():
...   global bar
...   bar = 1
...   baz = 2
... 
>>> dis.dis(foo)
  3           0 LOAD_CONST               1 (1)
              3 STORE_GLOBAL             0 (bar)

  4           6 LOAD_CONST               2 (2)
              9 STORE_FAST               0 (baz)
             12 LOAD_CONST               0 (None)
             15 RETURN_VALUE        
>>> def quux():
...   global bar
...   print bar
...   baz = 1
...   print baz
... 
>>> dis.dis(quux)
  3           0 LOAD_GLOBAL              0 (bar)
              3 PRINT_ITEM          
              4 PRINT_NEWLINE       

  4           5 LOAD_CONST               1 (1)
              8 STORE_FAST               0 (baz)

  5          11 LOAD_FAST                0 (baz)
             14 PRINT_ITEM          
             15 PRINT_NEWLINE       
             16 LOAD_CONST               0 (None)
             19 RETURN_VALUE

全局上下文python中使用的全局关键字

1 个答案: