名称未定义，即使使用全局变量？

Question

所以我试图写一个 function 来计算 pi 的估计值，然后从 pi 的实际值中减去。 但是，当我运行它时，我收到一条错误消息，提示未定义名称“piCalc”。 关于我做错了什么的任何想法？

import math
import random
def computePI (numThrows):
  circleCount = 0
  for i in range(numThrows):
      xPos = random.uniform (-1.0, 1.0)
      yPos = random.uniform (-1.0, 1.0)
      distance = math.hypot(xPos, yPos)
      if distance < 1:
        circleCount = circleCount + 1  
  piCalc =  4 * (circleCount/numThrows)
  return(piCalc)
def main():
  global piCalc
  throws = int(input(""))
  computePI(throws)
  difference = piCalc - math.pi
  print(piCalc)
  print(difference)
main()

Answer 1

尝试这样的事情，你会得到一个错误，因为你的价值不是全局的。 这样，computPI 无论如何都会返回 piccalc，因此您只需获取返回值即可。

import math
import random
def computePI (numThrows):
  circleCount = 0
  for i in range(numThrows):
      xPos = random.uniform (-1.0, 1.0)
      yPos = random.uniform (-1.0, 1.0)
      distance = math.hypot(xPos, yPos)
      if distance < 1:
        circleCount = circleCount + 1  
  piCalc =  4 * (circleCount/numThrows)
  return(piCalc)
def main():
   throws = int(input(""))
   calc = computePI(throws)
   difference = calc - math.pi
   print(calc)
   print(difference)
main()

Answer 2

您尚未在 function 中声明全局

import math
import random
def computePI (numThrows):
  global piCalc
  circleCount = 0
  for i in range(numThrows):
      xPos = random.uniform (-1.0, 1.0)
      yPos = random.uniform (-1.0, 1.0)
      distance = math.hypot(xPos, yPos)
      if distance < 1:
        circleCount = circleCount + 1  
  piCalc =  4 * (circleCount/numThrows)
  return(piCalc)
def main():
  global piCalc
  throws = int(input(""))
  computePI(throws)
  difference = piCalc - math.pi
  print(piCalc)
  print(difference)
main()

Answer 3

在主 function 中初始化 piCalc，代码表示 piCalc = 0

import math
import random
def computePI (numThrows):
  circleCount = 0
  for i in range(numThrows):
      xPos = random.uniform (-1.0, 1.0)
      yPos = random.uniform (-1.0, 1.0)
      distance = math.hypot(xPos, yPos)
      if distance < 1:
        circleCount = circleCount + 1  
  piCalc =  4 * (circleCount/numThrows)
  return(piCalc)
def main():
  global piCalc 
  piCalc = 0
  throws = int(input(""))
  computePI(throws)
  difference = piCalc - math.pi
  print(difference)
main()