为什么`letter =="A"或"a"`总是评估为True？

Question

请看代码.我正在使用机器人汽车来画一个字母,在这个代码中,当我输入b时,它仍然会画一个小案例a.

import create

# Draw a:
def drawa():
 #create robot
 robot = create.Create(4)
 #switch robot to full mode
 robot.toFullMode()
 for i in range(1280):
  robot.go(20,30)
 robot.stop()
 robot.move(-40,20)

# Draw b:
def drawb():
 #create robot
 robot = create.Create(4)
 #switch robot to full mode
 robot.toFullMode()
 robot.move(-100,20)
 for i in range(1270):
  robot.go(20,-30)
 robot.stop()

# Draw c:
def drawc():
 #create robot
 robot = create.Create(4)
 #switch robot to full mode
 robot.toFullMode()
 for i in range(700):
  robot.go(20,30)
 robot.stop()

# Define Main Function
def main():
 # While loop
 while(True):
  # Prompt user to enter a letter
  letter = raw_input("Please enter the letter you want to draw: ")
  # If user enters the letter a, draw a
  if letter=="A" or "a":
   drawa()
  # If user enters the letter b, draw b
  elif letter=="B" or "b":
   drawb();
  # If user enters the letter c, draw c
  elif letter=="C" or "c":
   drawc();
  # If user enters anything other than a letter from a-z,
  # ask them to enter a valid input
  else:
   print("Please enter a letter from a-z.")

main()

请帮忙.

Answer 1

这是因为你的条件.当你说...

if letter == "A" or "a"

......你其实在说......

if it's true that 'letter' equals 'A', or is true that 'a'

...并且"a",作为非空字符串,始终评估为true.你没有letter在右边那边问任何东西or.做这个:

if letter == "A" or letter == "a"

或者,因为我们在python中:

if letter in ["A", "a"]

干杯!