Python NameError, variable 'not defined'

问题:

the error it returns is:

NameError: name 'lives' is not defined

I know the code isn't as efficient as possible, this is one of my first projects, however whatever i try to do this error pops up, I've tried making a global for it but that didn't help. I would really appreciate some help with this, thanks!

import random
import time

def main():
 global guess,rand_num
 win = False
 rand_num = 45
 lives = 10
 while lives > 0 and win == False:
     guess = int(input("Guess a number!"))
     compare()
 print("Well done!")
 time.sleep(3)

def compare():
 global lives,win
 if guess == rand_num:
     print("You guessed correct!")
     win = True
 elif guess > rand_num:
     print ("Guess lower!")
     lives = lives - 1
 else:
     print ("Guess higher!")
     lives = lives - 1

def repeat():
 replay = input("would you like to play again? Y/N")
 if replay == "Y":
     print("enjoy!")
     main()
 elif replay == "N":
     "Goodbye then, hope you enjoyed!"
     time.sleep(3)
     os._exit
 else:
     print("please enter Y or N")
     repeat()

main()
repeat()

EDIT: putting global lives inside main() returns the error:

UnboundLocalError: local variable 'lives' referenced before assignment

回答1:

You need to define the variable "lives" outside of the function main, then any function where you want to reference that global variable you say "global lives." When you are in a function and assign a value to a variable, it assumes it is in the local scope. using "global lives" tells that function to look to the global scope as the reference of lives.

import random
import time

lives = 10
win = False
guess = 0
rand_num = 45

def main():
    global guess, rand_num, lives, win
    win = False
    rand_num = 45
    lives = 10
    while lives > 0 and win == False:
        guess = int(input("Guess a number!"))
        compare()
    print("Well done!")
    time.sleep(3)

def compare():
    global guess, rand_num, lives, win
    if guess == rand_num:
        print("You guessed correct!")
        win = True
    elif guess > rand_num:
        print ("Guess lower!")
        lives = lives - 1
    else:
        print ("Guess higher!")
        lives = lives - 1

def repeat():
    replay = input("would you like to play again? Y/N")
    if replay == "Y":
        print("enjoy!")
        main()
    elif replay == "N":
        "Goodbye then, hope you enjoyed!"
        time.sleep(3)
        os._exit
    else:
        print("please enter Y or N")
        repeat()

main()
repeat()

回答2:

You didn't declare lives to be global inside main(), so it is local to that function.

def main():
    global guess, rand_num, lives
    ...

回答3:

When you declare it inside function they are only available in that function scope, so declare global variables outside functions and code will work fine.

import random
import time

guess = None
random_num = None
lives = 3
win = False


def main():
 global guess,rand_num
 win = False
 rand_num = 45
 lives = 10
 while lives > 0 and win == False:
     guess = int(input("Guess a number!"))
     compare()
 print("Well done!")
 time.sleep(3)

def compare():
 global lives,win
 if guess == rand_num:
     print("You guessed correct!")
     win = True
 elif guess > rand_num:
     print ("Guess lower!")
     lives = lives - 1
 else:
     print ("Guess higher!")
     lives = lives - 1

def repeat():
 replay = input("would you like to play again? Y/N")
 if replay == "Y":
     print("enjoy!")
     main()
 elif replay == "N":
     "Goodbye then, hope you enjoyed!"
     time.sleep(3)
     os._exit
 else:
     print("please enter Y or N")
     repeat()

main()
repeat()

And now this works fine. For more info about gloval vs local variables you can read: http://www.python-course.eu/global_vs_local_variables.php