Question

我正在编写一个程序来控制连接到树莓派的两个步进电机的相机。我在python中写作，我在理解全局变量（或python中的名字，我猜）时遇到了麻烦。我已经查看了有关范围和全局变量的一些内容，但我对使用python进行编程真的很陌生，而且它对我来说并不完全有意义。我有一个程序＆＃34; MainProgram＆＃34;为变量D_Alt赋值。然后该程序从模块＆＃34; stepper＆＃34;调用一个函数。该函数需要使用D_Alt。我将D_Alt设置为主程序中的全局变量，但我仍然收到错误。如何设置D_Alt以便主程序和模块可以使用它？

以下是主程序的代码：

doSomething

这是我需要使用的模块的功能：

from astropy.io import fits
import os
import RPi.GPIO as GPIO
import time
import math
import sys
import stepper

global In_Alt, In_Az, C_Alt, C_Az, D_Alt, D_Az

#start server and get initial position
os.system("indi.sh")
os.system("indi.takepic.sh %s %s" %(15, "InitialPosition"))
os.system("platesolve.sh %s" %("InitialPosition"))
stepper.initPosition()
stepper.initPins()

list_of_stars = [[0,0],[1,1],[2,2]]     #star in list_of_stars is [RA,D]
for star in list_of_stars:
    D_Az=star[0]                        #
    D_Alt=star[1]
    print D_Az
    print D_Alt
    stepper.moveMotor()
    for x in range(0,10):
        os.system("indi.takepic.sh {0}+str(x) .format(list_of_stars[star])")      #take pic with 15s exposure and rename with name of star and number
    stepper.resetPosition()
    os.system("indi.takepic.sh 15 ResetPosition")
    os.system("platesolve.sh ResetPosition")
GPIO.cleanup()
sys.exit(0)

我得到的错误是：

def moveMotor():
    #move altitude motor
    global D_Alt
    result = D_Alt - C_Alt            #find number of steps to move
    if(result>0):                    #if number of steps is positive, move forward
        steps = result
        forward(int(delay) / 1000.0, int(steps), C_Alt)
        C_Alt = C_Alt + steps
    else:                            #if number of steps is negative, move backward
        steps = abs(result)          #steps must be positive, so turn result into positive number
        backwards(int(delay) / 1000.0, int(steps), C_Alt)
        C_Alt = C_Alt - steps

Answer 1

global语句是声明，它包含整个当前代码块。这意味着列出的标识符将被解释为全局变量。

您仍然需要在某处定义标识符。这是您得到的错误：global name 'D_Alt' is not defined，您尚未定义变量。

通过在模块根目录中定义变量而不是在函数或其他代码块中，您可以将整个模块作为只读进行访问。但是，要在不同的代码块中修改它，您需要在代码块中将其声明为全局。

试试这个：

from astropy.io import fits import os import RPi.GPIO as GPIO import time import math import sys import stepper # Defining the variables In_Alt = None In_Az = None C_Alt = None C_Az = None D_Alt = None D_Az = None delay = None def forward(someArgs): .. your implementation .. def backwards(someArgs): ..your implementation.. def moveMotor(): #move altitude motor global D_Alt, C_Alt, delay result = D_Alt - C_Alt #find number of steps to move if(result>0): #if number of steps is positive, move forward steps = result forward(int(delay) / 1000.0, int(steps), C_Alt) C_Alt = C_Alt + steps else: #if number of steps is negative, move backward steps = abs(result) #steps must be positive, so turn result into positive number backwards(int(delay) / 1000.0, int(steps), C_Alt) C_Alt = C_Alt - steps # start server and get initial position os.system("indi.sh") os.system("indi.takepic.sh %s %s" % (15, "InitialPosition")) os.system("platesolve.sh %s" % ("InitialPosition")) stepper.initPosition() stepper.initPins() list_of_stars = [[0, 0], [1, 1], [2, 2]] # star in list_of_stars is [RA,D] for star in list_of_stars: D_Az = star[0] # D_Alt = star[1] print D_Az print D_Alt stepper.moveMotor() for x in range(0, 10): os.system( "indi.takepic.sh {0}+str(x) .format(list_of_stars[star])") # take pic with 15s exposure and rename with name of star and number stepper.resetPosition() os.system("indi.takepic.sh 15 ResetPosition") os.system("platesolve.sh ResetPosition") GPIO.cleanup() sys.exit(0)

您可以在此处找到有关global的更多信息：https://docs.python.org/2/reference/simple_stmts.html#global

如何在主程序中定义的模块中使用变量？

1 个答案: