python：未定义全局名称“ user_input”

Question

I keep getting the error message "global name 'user_input' not defined. new to python and to SO, hope you can help. Here's my code. Sorry if it's a mess. just starting out and teaching myself...

def menu():
    '''list of options of unit types to have converted for the user
    ex:
    >>> _1)Length
        _2)Tempurature
        _3)Volume
    '''

    print('_1)Length\n' '_2)Temperature\n' '_3)Volume\n' '_4)Mass\n' '_5)Area\n'
          '_6)Time\n' '_7)Speed\n' '_8)Digital Storage\n')

    ask_user()
    sub_menu(user_input)

def ask_user():
    ''' asks the user what units they would like converted
    ex:
    >>> what units do you need to convert? meter, feet
    >>> 3.281
    '''
    user_input = input("Make a selection: ")
    print ("you entered",  user_input)
    #conversion(user_input)
    return user_input

def convert_meters_to_feet(num):
    '''converts a user determined ammount of meters into feet
    ex:
    >>> convert_meters_to_feet(50)
    >>> 164.042
    '''

    num_feet = num * 3.28084
    print(num_feet)


def convert_fahrenheit_to_celsius(num):
    '''converts a user determined temperature in fahrenheit to celsius
    ex:
    >>> convert_fahrenheit_to_celsius(60)
    >>> 15.6
    >>> convert_fahrenheit_to_celsius(32)
    >>> 0
    '''

    degree_celsius = (num - 32) * (5/9)
    print(round(degree_celsius, 2))


def sub_menu(num):
    '''routes the user from the main menu to a sub menu based on
    their first selection'''

    if user_input == '1':
        print('_1)Kilometers\n' '_2)Meters\n' '_3)Centimeters\n' '_4)Millimeters\n'
              '_5)Mile\n' '_6)Yard\n' '_7)Foot\n' '_8)Inch\n' '_9)Nautical Mile\n')

        ask = input('Make a selection (starting unit)')
        return
    if user_input == '2':
        print('_1)Fahrenheit\n' '_2)Celsius\n' '_3)Kelvin\n')
        ask = input('Make a selection (starting unit)')
        return

Answer 1

在menu功能中，将显示ask_user()的行更改为user_input = ask_user() 。

Answer 2

When you do:

user_input = input("Make a selection: ")

Inside the ask_user() function, you can only access user_input inside that function. It is a local variable, contained only in that scope.

If you want to access it elsewhere, you can globalise it:

global user_input
user_input = input("Make a selection: ")

---

I think what you were trying was to return the output and then use it. You kind of got it, but instead of ask_user() , you have to put the returned data into a variable. So:

user_input = ask_user()

THere's no need to globalise the variable (as I showed above) if you use this method.