Python: NameError“”未定义

Question

好的，所以我希望程序的最终结果如下所示...

现在，我不需要那些确切的数字，因为这会将机器人置于模拟中，因此结果应该会有所不同。

这是我的代码：

# This program makes the robot calculate the average amount of light in a simulated room

from myro import *
init("simulator")

from random import*

def pressC():
    """ Wait for "c" to be entered from the keyboard in the Python shell """
    entry = " "
    while(entry != "c"):
        entry = raw_input("Press c to continue. ")
    print("Thank you. ")
    print

def randomPosition():
    """ This gets the robot to drive to a random position """
    result = randint(1, 2)
    if(result == 1):
        forward(random(), random())
    if(result == 2):
        backward(random(), random())

def scan():
    """ This allows the robot to rotate and print the numbers that each light sensors obtains """
    leftLightSeries = [0,0,0,0,0,0]
    centerLightSeries = [0,0,0,0,0,0]
    rightLightSeries = [0,0,0,0,0,0]
    for index in range(1,6):
        leftLight = getLight("left")
        leftLightSeries[index] = leftLightSeries[index] + leftLight
        centerLight = getLight("center")
        centerLightSeries[index] = centerLightSeries[index] + centerLight
        rightLight = getLight("right")
        rightLightSeries[index] = rightLightSeries[index] + rightLight
        turnRight(.5,2.739)
    return leftLightSeries, centerLightSeries, rightLightSeries

def printResults():
    """ This function prints the results of the dice roll simulation."""
    print " Average Light Levels "
    print "    L      C      R "
    print "========================="
    for index in range(1, 6):
        print str(index) + " " + str(leftLightSeries[index]) + " " + str(centerLightSeries[index]) + " " + str(rightLightSeries[index])

def main():
    senses()
    pressC()
    randomPosition()
    leftLightSeries, centerLightSeries, rightLightSeries = scan() 
    printResults()

main()

而且，当我运行我的代码时出现此错误：

Traceback (most recent call last):
  File "C:/Users/Owner-pc/Desktop/Computer Programming 1/Mod05/Code/Created/AverageLight.py", line 58, in -toplevel-
    main()
  File "C:/Users/Owner-pc/Desktop/Computer Programming 1/Mod05/Code/Created/AverageLight.py", line 56, in main
    printResults()
  File "C:/Users/Owner-pc/Desktop/Computer Programming 1/Mod05/Code/Created/AverageLight.py", line 49, in printResults
    print str(index) + " " + str(leftLightSeries[index]) + " " + str(centerLightSeries[index]) + " " + str(rightLightSeries[index])
NameError: global name 'leftLightSeries' is not defined

所以，我很困惑为什么我的 return 语句不起作用，为什么我没有得到我想要的列表。请帮忙。

Answer 1

您在函数 scan() 中定义了 leftLightSeries 和 centerLightSeries。由于它们未在外部作用域（在本例中为全局作用域）中定义，函数 printResults 无法访问它们。

Python 文档在 4.2.2. Resolution of names

部分对其进行了描述

A scope defines the visibility of a name within a block. If a local variable is defined in a block, its scope includes that block. If the definition occurs in a function block, the scope extends to any blocks contained within the defining one, unless a contained block introduces a different binding for the name.

When a name is used in a code block, it is resolved using the nearest enclosing scope. The set of all such scopes visible to a code block is called the block’s environment.

When a name is not found at all, a NameError exception is raised. If the current scope is a function scope, and the name refers to a local variable that has not yet been bound to a value at the point where the name is used, an UnboundLocalError exception is raised. UnboundLocalError is a subclass of NameError.

Answer 2

leftLightSeries、centerLightSeries 和 rightLightSeries 未在 printResults 的范围内定义，这就是您收到该错误的原因。

更新您的 printResults 函数以接受这些参数：

def printResults(leftLightSeries, centerLightSeries, rightLightSeries):

稍后，当您调用 printResults 时，将这些变量传入：

def main():
    ...
    printResults(leftLightSeries, centerLightSeries, rightLightSeries)

现在的问题是，您仍然没有在 main 范围内定义这 3 个变量，它们仅在 scan 内定义。你如何让他们离开 scan？只需将 scan 的 return 值存储在变量中，如下所示：

def main():
    senses()
    pressC()
    randomPosition()
    leftLightSeries, centerLightSeries, rightLightSeries = scan() 
    printResults(leftLightSeries, centerLightSeries, rightLightSeries)

你也可以直接将scan的输出发送到printResults而不需要临时变量：printResults(*scan())

Answer 3

您遇到的问题是 scoping 问题。

leftLightSeries 是在函数 scan() 的范围内定义的，这意味着它只能从该函数内访问。所以在函数范围内不可用printResults().

您的代码的另一个问题是您有多个 return 永远不会达到的语句：

return leftLightSeries
return centerLightSeries
return rightLightSeries

此代码块将 return leftLightSeries 然后永远不会到达接下来的两个 return 语句。如果想要 return 多个值，您可以考虑的一种选择是 return 一个元组：

return (leftLightSeries, centerLightSeries, rightLightSeries,)

然后在 printResults() 你可以像这样获取你的系列：

leftSeries, centerSeries, rightSeries = scan()

for index in range(0,6):
    print str(index) + " " + str(leftSeries[index]) + " " + str(centerSeries[index]) + " " + str(rightSeries[index])

另请注意，range(0,6) 是您想要的，而不是范围 (1,6)。数组从索引 0 开始，range 为您提供从第一个参数到但不包括第二个参数的范围。

Python: NameError“”未定义

Python: NameError ' ' is not defined

python

nameerror