Passing variables between functions: recall returned variables or use classes?

Question

I have found a simple way to pass variables between functions.

However, I am curious to see if another way is simpler, for example by creating a class. Or, indeed, if my approach to pass variables is problematic.

I was recently struggling to understand how variables can be passed between functions.

There are several StackOverflow questions for newbies on this issue (see here, here, and here). Many answers, however, tend to be too specific to the code snippet provided by the questioner.

I want to understand the general workflow. That is, how variableA can be passed to functionA, manipulated, then passed to functionB, changed again, and then output in functionC, for example.

I think I have a solution:

def main():
    output()

def function1():
    sentence = ("This is short.")   # here is a string variable
    value = (10)                    # here is a number variable
    return sentence, value          # they are returned

def firstAddition():
    sentence, value = function1()   # variables recalled by running function1()
    add1stSentence = "{}at is longer.".format(sentence[0:2]) # string changed
    add1stValue = 2 * value                                  # number changed
    return add1stSentence, add1stValue    # the changed values are returned

def secondAddition():               # This function changes variables further
    add1stSentence, add1stValue = firstAddition()
    add2ndSentence = "{} This is even longer.".format(add1stSentence)
    add2ndValue = 2 * add1stValue
    return add2ndSentence, add2ndValue

def output():                       # function recalls all variables and prints
    sentence, value = function()
    add1stSentence, add1stValue = firstAddition()
    add2ndSentence, add2ndValue = secondAddition()
    print(sentence)
    print(str(value))
    print(add1stSentence)
    print(str(add1stValue))
    print(add2ndSentence)
    print(str(add2ndValue))

The output of the above code is the following:

This is short. 10 That is longer. 20 That is longer. This is even longer. 40

The original sentence and value variables were passed between the functions.

My way for passing variables has four steps:

build functionA that manipulates variables;
return those variables at the end of functionA;
at start of functionB, recall each variable, which = functionA;
functionB manipulates variables and returns them again to be further manipulated, or outputs the variables.

My questions are:

(a) Is my way an accepted practice?

(b) Is there a better or more elegant way to pass variables between functions?

Explicit is much, much better than implicit. You hide all data passing with this method, that makes your code much harder to understand. Furthermore, you remove all flexibility by hardcoding the the source of the data in each function. In short: use parameters. :) — Thierry Lathuille, Apr 05 '19 at 19:54
@DYZ Cheers. I've just found this which introduces them. https://stackoverflow.com/questions/919680/can-a-variable-number-of-arguments-be-passed-to-a-function — P Braga, Apr 05 '19 at 20:06
@ThierryLathuille Okay. Using parameters appears to be the consensus. Nick Vitha, who responded below, is telling me the same thing. — P Braga, Apr 05 '19 at 20:09

score 0 · Answer 1 · answered Apr 05 '19 at 19:52

The way to pass variables into functions are through function arguments (also known as function parameters).

In your case, you can modify functionB to accept inputs. Your example is a bit complex, but I'll boil it down slightly easier to understand for you.

Right now, you are essentially doing something like this:

def functionA():
    return 12

def functionB():
    return 5

def caller():
    holder = functionA() + functionB()
    print(holder)

In general, this will work, but it's much more preferred to do something like:

def functionA():
   return 5

def functionB(number):
   return(number+5)

def caller():
   holder = functionA()
   output = functionB(holder)
   print(output)

or even:

def caller():
   print(functionB(functionA()))

You can pass outputs of functions to other functions.

I'd read a bit more about python functions https://www.tutorialspoint.com/python3/python_functions.htm before continuing on to more complex things.

Thank you very much, Nick. Much appreciated for your speedy reply. — P Braga, Apr 05 '19 at 20:10

Passing variables between functions: recall returned variables or use classes?

1 Answers1