python - if/elif 语句和turtle 命令出错

Question

我在 if/else 语句中遇到了一个奇怪的错误。由于某种原因，当我使用此代码时( turtle 图形介绍项目)

from turtle import *
print('Hello. I am Terry the Turtle. Enter a command to make me draw a line, or ask for help.')
on = True
shape('turtle')
if on == True:
   c1 = str(input('Enter command: ')
   if c1 == 'forward':
      c2 = eval(input('How many degrees? ' ))
      right(c2)
   elif c1 == 'right':
      c2 = eval(input('How many degrees? ' ))
      right(c2)
   elif c1 == 'left':
      c2 = eval(input('How many degrees? ' ))
      left(c2)
   elif c1 == 'goodbye':
      print('Bye!')
      on = False
   else:
      print('Possible commands: forward, right, left, goodbye.')

出于某种奇怪的原因，if 和 elif 语句不断返回语法错误，但它们似乎没有任何可见错误。我尝试做类似的事情，但它不断返回语法错误。有什么办法可以解决这个问题吗？

抱歉，如果这是一个愚蠢的问题，这是我第一次来这里，我真的很困惑。

Answer 1

我想这就是你想要的

from turtle import *
print('Hello. I am Terry the Turtle. Enter a command to make me draw a line, or ask for help.')
on = True
shape('turtle')
# Get commands until user enters goodbye
while on:
    c1 = str(input('Enter command: '))
    if c1 == 'forward':
        # Ask how far when moving
        c2 = int(input('How far? '))
        # Use forward to move
        forward(c2)
    elif c1 == 'right':
        c2 = int(input('How many degrees? '))
        right(c2)
    elif c1 == 'left':
        c2 = int(input('How many degrees? '))
        left(c2)
    elif c1 == 'goodbye':
        print('Bye!')
        on = False
    else:
        print('Possible commands: forward, right, left, goodbye.')

这应该使用 Python3 运行(例如 python3 myrtle.py)。