Question

错误：

local variable 'num1' referenced before assignment.

我尝试制作一个单独的函数，但是它不起作用（或者至少我无法使它起作用）。

def main():

  while True:
    try:
      num1=int(input('.+'))

    except ValueError:
      print('Sorry, this progam only accepts values between 0 and 100.')
    if num1 < 0:
      return ('Sorry this program only accepts values between 0 and 100.')
    else:
      break 

  if num1 >= 90:
    return ('Your letter grade is A')
  if num1 >= 80:
    return ('Your letter grade is B')
  elif num1 >= 70:
    return ('Your letter grade is C')
  elif num1 >= 60:
    return ('Your letter grade is D')
  if num1 <=60:
    return ('Your letter grade is F')

print(main())

Answer 1

我假设这是在您输入无法转换为int的字符串时发生的。因此它进入try块，然后（不设置num1）引发异常，然后继续。稍后，您尝试访问未设置的num1。

您可以将数字设置为默认值：

while True:
    try:
        num1 = int(input())
    except ValueError:
        num1 = -1

    if num < 0:
        print('Please input a valid number between 0 - 100')
    else:
        break

这将使它每次无效输入仅警告用户一次，并不断提示直到他们输入有效数字

Answer 2

如果您第一次输入无效数字，则会发生错误。在这种情况下，永远不会定义变量num1。

要解决此问题，您可以在while循环外定义一次变量，如下所示：

num1 = -1
while True:
    ...

Answer 3

稍微清洁了代码。

def my_func():

  while True:
    try:
      this_input=int(input('.+'))
    except ValueError:
      print('Sorry, this progam only accepts values between 0 and 100.')
    if this_input < 0 or this_input > 100:
      return ('Sorry this program only accepts values between 0 and 100.')
    else:
      break 

  if this_input >= 90:
    return ('Your letter grade is A')
  elif this_input >= 80:
    return ('Your letter grade is B')
  elif this_input >= 70:
    return ('Your letter grade is C')
  elif this_input >= 60:
    return ('Your letter grade is D')
  elif this_input <=60:
    return ('Your letter grade is F')
  elif this_input > 100:
    return ("Value out of bounds")
  else:
    return ""


print(my_func())

由于输入了除int之外的其他内容，因此出现错误。

daudnadeem:use_me_to_code_tests daudn$ python3 mail.py
.+A
Sorry, this progam only accepts values between 0 and 100.
Traceback (most recent call last):
  File "mail.py", line 30, in <module>
    print(my_func())
  File "mail.py", line 9, in my_func
    if this_input < 0 or this_input > 100:
UnboundLocalError: local variable 'this_input' referenced before assignment
daudnadeem:use_me_to_code_tests daudn$ python3 mail.py
.+100
Your letter grade is A

分配前已引用局部变量“ num1”

3 个答案: