Python 为什么我的“for”循环没有完全遍历？

我对python非常陌生，一直致力于密码学。我正在编写一个Caesar密码，但代码快结束时，它停止工作，只加密字符串中的1个字符

为什么会这样？ 我怎样才能修好它

during = []
preBool = True
while preBool == True :
    pre = str(input("Enter your message: "))
    if pre.isalpha() == False:
        print("\nSorry, your input was not recognized.")
        print("-------------------------------------------------------")
        continue
    else:
        preBool = False
for char in pre:
    during.append(char)
print(during)

while True:
    try:
        rot = int(input("Enter the rotation value: "))
    except ValueError:
        print("Sorry, your input was not recognized.")
        continue
    else:
        break
#Here is where I'm having issues. 'Cipher' only prints the first letter.
def encrypt(pre,rot):
   result = ""
   # transverse the plain text
   for i in range(len(pre)):
      char = pre[i]
      # Encrypt uppercase characters in plain text

      if (char.isupper()):
         result += chr((ord(char) + rot-65) % 26 + 65)
      # Encrypt lowercase characters in plain text
      else:
         result += chr((ord(char) + rot - 97) % 26 + 97)
      return result

print ("Cipher: " + encrypt(pre,rot))

返回结果在for循环内。当代码命中它时，它无条件地退出函数，在过程中中断循环

将其缩进一级，for循环应按预期运行，并且仅在其运行完其自然过程后返回