如何使用函数解决这个 Python 问题？ [复制]

Question

import json

def get_stored_username():
    """Get stored username if available."""
    filename = 'username.json'
    try:
        with open(filename) as f_obj:
            username = json.load(f_obj)
    except FileNotFoundError:
        return None
    else:
        return username

def get_new_username():
    """Prompt for a new username."""
    username = input("What is your name? ")
    filename = 'username.json'
    with open(filename, 'w') as f_obj:
        json.dump(username, f_obj)
    return username

def greet_user():
    """Greet the user by name."""
    username = get_stored_username()
    if username:
        correct = input("Are you " + username + "? (y/n) ")
        if correct == 'y':
            print("Welcome back, " + username + "!")
            return

    # We got a username, but it's not correct.
    # Let's prompt for a new username.
    username = get_new_username()
    print("We'll remember you when you come back, " + username + "!")


greet_user()

上面代码中的函数greet_user()应该根据下面的文字重写：

唯一需要解决的是嵌套的if 语句。这可以通过将检查用户名是否正确的代码移动到单独的函数来清除。如果您喜欢这个练习，您可以尝试创建一个名为 check_username() 的新函数，看看是否可以从 greet_user() 中删除嵌套的 if 语句。

这是我试图解决这个问题的尝试：

def greet_user():
    """Greet the user by name."""
    username = get_stored_username()
    if username:
        check_username()
    username = get_new_username()
    print("We'll remember you when you come back, " + username + "!")

def check_username():
    correct = input("Are you " + username + "? (y/n) ")
    if correct == 'y':
        print("Welcome back, " + username + "!")
    username = get_new_username()
    print("We'll remember you when you come back, " + username + "!")

这是 IDLE 的输出：

Traceback (most recent call last):
  File "C:\Users\Documents\python_work\files and exceptions\JSON\remember_me.py", line 41, in <module>
    greet_user()
  File "C:\Users\Documents\python_work\files and exceptions\JSON\remember_me.py", line 29, in greet_user
    check_username()
  File "C:\Users\Documents\python_work\files and exceptions\JSON\remember_me.py", line 34, in check_username
    correct = input("Are you " + username + "? (y/n) ")
UnboundLocalError: local variable 'username' referenced before assignment

程序应该是这样工作的：

What is your name? eric
We'll remember you when you come back, eric!

Are you eric? (y/n) y
Welcome back, eric!

Are you eric? (y/n) n
What is your name? ever
We'll remember you when you come back, ever!

Are you ever? (y/n) y
Welcome back, ever!

Answer 1

您在该范围内没有变量 username。您在great_user 中有一个同名的局部变量，但您还没有将它传递给check_username。只需添加该参数/参数。

def greet_user():
    """Greet the user by name."""
    username = get_stored_username()
    if username:
        check_username(username)
    username = get_new_username()
    print("We'll remember you when you come back, " + username + "!")

def check_username(username):
    correct = input("Are you " + username + "? (y/n) ")
    if correct == 'y':
        print("Welcome back, " + username + "!")
    username = get_new_username()
    print("We'll remember you when you come back, " + username + "!")

另外，您的流量控制很不舒服。 check_username 应该只做这么多，返回其状态，并让新用户的注册保留已为此目的编写的函数。