python - 一旦满足条件，循环将无法终止

Question

我试图让我的函数在遇到 return 子句时结束循环，但它没有这样做。解释而不是直接代码编辑将不胜感激。

def Menu():
    UserMenu = True
    print (""" 
        U.Create a Username
        E.Run Exponential Calculator
        Q.Exit/Quit 
        """)
    while UserMenu not in ("U", "E", "Q"):
        print("\n Error: Choice must be U, E or Q")
    return UserMenu

# Function designed to retrieve first name only from fullname entry.
def get_first_name(name):
    first=[""]
    i = 0 
    while i < len(name) and name[i] !=" ":
        first += name[i]
        i += 1
    return name[:i]

# Function designed to retrieve first initial of last name or first initial of first name if only one name input.
def get_last_initial(name):
    j = len(name) - 1 
    while j >= 0 and name[j] !=" ":
        j-=1
    return name[j+1]


# Function that generates username based upon user input.
def get_username():
    name = raw_input("Please enter your Full Name: ") 
    username = get_first_name(name) + get_last_initial(name) 
    return username.lower()



# Function to generate exponential numbers based upon usser input.
def print_exponential(): 
    base = int(raw_input("Please select a base number: \n")) 
    power = int(raw_input("Please select a power number: \n")) 
    exponential = 1 
    while power>0: 
        exponential = exponential * base 
        print base 
        if power >1:
            print "*",
        power = power -1 
    return "=%d" % exponential

print Menu()
while UserMenu != "Q":
    if UserMenu is "U":
        UserMenu = raw_input("Please enter your Full Name: ")
        print "your username is %s" % get_username()
    else:
        print print_exponential()
    print Menu()

这就是整个程序，希望对您有所帮助!

Answer 1

需要在循环内更新UserMenu的值，否则进入循环本身就是死循环:

def Menu():
    UserMenu = raw_input(""" 
        U.Create a Username
        E.Run Exponential Calculator
        Q.Exit/Quit 
        """)
    while UserMenu not in ("U", "E", "Q"):
        UserMenu = raw_input("\n Error: Please input only U, E or Q:")
    return UserMenu


...
all your other functions
...

user_choice = Menu()
while user_choice != "Q":
    if user_choice == "U":
        print "your username is %s" % get_username()
    else:
        print_exponential()
    user_choice = Menu()

通过在循环中获取新的输入，它将能够满足控制循环的条件。您编写的循环将只打印然后再次检查 UserMenu 而不更改它，因此循环永远不会退出。