为什么我的变量显示为“未定义”？

Question

I have made an input variable as a number but only if the number 2 is inputted, it shows this:

  line 35, in <module>
    if num_b == legal_num:
NameError: name 'num_b' is not defined"

I am not sure why it shows this.

print ("This is the popular 60's game Nim")
print ("The aim of the game is for you to get to zero")

nim_rules = ("Rules:", "The human always gets the luxury to start", "You can only take away 1, 2, or 3 in 1 turn", "As you know, the person who gets to zero wins")
 
for rules in nim_rules:
     print (rules)

num_a = input ("Type your number: 1, 2, 3: ")
num_a = int(num_a);

legal_numbers = [1, 2, 3]
for legal_num in legal_numbers:

     if num_a == legal_num:
          C_num_a = 4 - num_a
          print (f" I take away {C_num_a}")
          num_b = input ("The number 8 is left. Choose your next number: ")
          num_b = int(num_b);

     if num_b == legal_num:
          C_num_b = 4 - num_b
          print (f"I take away {C_num_b}")
          num_c = input ("The number 4 is left. Choose your next number: ")
          num_c = int(num_c);
     
     if num_c == legal_num:
          C_num_c = 4 - num_c
          print (f"I take away {C_num_c}")
          print ("I win. Please Try again - You might win next time!")

else:
     print ("Is that the number 1, 2, or 3? Try again. ")

Answer 1

您只定义num_b当num_a == legal_num 。

Answer 2

You have only defined a variable "num_a" in this snippet as global var:

num_a = input ("Type your number: 1, 2, 3: ")
num_a = int(num_a);

While num_b and num_c are defined with local scope within if condition.

You need to define these variables globally.

num_a = input ("Type your number: 1, 2, 3: ")
num_a = int(num_a);

num_b = None;
num_c = None;
for legal_num in legal_numbers:

   if num_a == legal_num:
      C_num_a = 4 - num_a
      print (f" I take away {C_num_a}")
      num_b = input ("The number 8 is left. Choose your next number: ")
      num_b = int(num_b);
   ..........

Answer 3

您只需num_b初始化变量num_b和num_c 。

Answer 4

The way your program has been define, num_b and num_c will be defined only if num_a == legal_name

You may want to revisit your if statement implementation.

Do you want to left indent the num_b and num_c input statements?

To help you, i have added a comment before those statements.

Your code below. I have added comments using #

num_a = input ("Type your number: 1, 2, 3: ")
num_a = int(num_a);

legal_numbers = [1, 2, 3]
for legal_num in legal_numbers:

     if num_a == legal_num:
          C_num_a = 4 - num_a
          print (f" I take away {C_num_a}")

          #should the next two lines be left intend or go outside the for loop

          num_b = input ("The number 8 is left. Choose your next number: ")
          num_b = int(num_b);

     if num_b == legal_num:
          C_num_b = 4 - num_b
          print (f"I take away {C_num_b}")

          #should the next two lines be left intend or go outside the for loop

          num_c = input ("The number 4 is left. Choose your next number: ")
          num_c = int(num_c);
     
     if num_c == legal_num:
          C_num_c = 4 - num_c
          print (f"I take away {C_num_c}")
          print ("I win. Please Try again - You might win next time!")