Python - Function Return Value

问题

This example is just a basic program - I'm a new Coder - learning and experimenting whilst messing about .. Currently testing on Python 3.6 IDE and PyCharm - apologies for double spacing code - but looks a mess without.

Looking for guidance for returning a value from a function.

Have tried dozens of different methods / searched the forum, but closest answer this layman could understand stated I needed to use the return value otherwise it will be forgotten .. So added print(age_verification, " example test value .. ") at various locations - but nothing gets returned outside the function ..

Have tried returning Boolean / integer / string values and adapting - nothing with each variant .. Added a default age_verification = False variable before the function // or // referenced within function for 1st time .. Doesn't effect the return value except IDE doesn't state "unresolved reference"

Tried a line-by-line python visualizer - but again - age_verification value disappears instantly after exiting the function . :-(

==================================================================

Using 1 Single Function

def age_veri(age, age_verification) :

  if age < 18 :

    age_verification = False

    print(age_verification, " is false .. Printed to test variable ..")

    return age_verification

  elif age >= 18:

    age_verification = True

    print(age_verification, " is True.. Printed to test variable ..")

    return age_verification

  return age_verification # ( -- have tested with/without this single-indent line & with/without previous double-indent return age_verification line.)

age=int(input("Enter Your Age : ")

age_verification = False # ( -- have tried with / without this default value)

age_veri(age, False)

if age_verification is False:

  print("You failed Verification - Age is Below 18 .. ")

elif age_verification is True:

  print("Enter Website - Over 18yrs")

else:

  print(" Account not Verified .. ")

==================================================================

Same Example - Using 2 Functions

def age_variable(age):

   if age < 18:

      age_verification = False

      print (age_verification, " printing here to use value and help test function..")

      return age_verification

   elif age >= 18:

      age_verification = True

      print (age verification, " printing here to use value and help test function..")

      return age_verification

   return age_verification (tried with and without this line - single indent - same level as if / elif) 

def are_verified(age_verification):

   if age_verification is False:

      print("Age Verification Failed .. ")

   elif age_verification is True:

      print("Visit Website .. ")

   else:

      print("Verification Incomplete .. ")

age = int(input("Enter Your Age : ")

age_variable(age)

are_verified(age_verification)

==============================================================

Any advice is appreciated - wasted most of today hitting my head against the wall .. And apologies in advance .. Know it'll be something really basic - but appear to be using same formatting as others :-)

THANK YOU

回答1:

print doesn't return values, it will just display the value to stdout or the console. If you want to return a value with conditions, understanding scope is helpful. Your comment regarding returning variables otherwise they will be "forgotten" is correct. Variables defined and not returned by the function will go away when the function executes:

def my_func(var1):
    var2 = var1
    var3 = 5
    return var3

print(my_func(1), var2)

The print statement will throw a NameError because var2 isn't defined outside of the function, nor is it returned. For your example, you'd want something like this:

def age_verify(age):
    if age < 18:
        print("Failed Verification")
        return False
    else:
        print("Verification Complete")
        return True

# Call and assign to var
age = int(input("Enter Your Age : ")
age_verification = age_verify(age)

This way you are saving the returned value as the variable age_verification

EDIT:

To further expand on the scope concept, using the same definition for my_func:

def my_func(var1):
    var2 = var1
    var3 = 5
    return var3

We assign the returned var3 to a variable like so:

myvar = my_func(5)

As noted, the name var3 isn't actually returned, just the value. If I were to run

myvar = my_func(5)
print(var3)

I would get a NameError. The way to get around that would be to do:

var3 = my_func(5)

because now var3 is defined in global scope. Otherwise, I would have to edit my function to make var3 global:

def my_func(var1):
    global var3
    var2 = var1
    var3 = 5
    # The return statement is then a bit redundant

my_func(5)

print(var3)
# prints 5 in global scope

Hopefully this is a bit clearer than my original answer

来源：https://stackoverflow.com/questions/52209825/python-function-return-value

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