名称未定义，即使使用全局变量？

Question

所以我试着写一个函数来计算pi的估计值，然后从pi的实际值中减去。然而，当我运行它时，我得到一个错误，说名称“piCalc”没有定义。你知道我做错了什么吗

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

您尚未在函数中声明全局

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 2

尝试这样的操作，您会得到一个错误，因为您的值不是全局的。这样，computPI无论如何都会返回picalc，因此您只需捕获返回值即可

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 3

在主函数和代码中初始化piCalc 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()