What issues can arise when you call a function within a function?

Question

I’m in the process of learning coding and below we have a simple conversion between Fahrenheit and Celsius. I have created a loop in the check function that will call the convert function again if the user inputs something in the confirm array (I removed the arrays to save space).

From what I’ve been told it is better coding practice to have something like a do-while loop as opposed to calling functions within functions.

So I’m wondering what issues could arise with functions within functions that new people may not think of.

def convert():

    while True:
        usrchoice = input("Would you like to change Cel or Far? :")
        if usrchoice in Celsius:
            usrcel = int(input("Input temp in Celc: "))
            far = usrcel * (9.0/5.0) +32
            print("that's " + str(far) + " degrees in Far")   
            break
        elif usrchoice in Far:
            usrfar = int(input("Input temp in Far: "))
            cel = (usrfar - 32) / (9.0/5.0)
            print("that's " + str(cel) + " degrees in Cel" )
            break
        else: print("Choose Cel or Far")
        continue



def check():

    while True:
        dblchk = input("Would you like to make another conversion? ")
        if dblchk in Confirm:
            convert()                                                           
        elif dblchk in Deny:
            print("Conversion finished")
            break
        else: print("Please enter yes or no")
        continue


convert()

check()

Asked By: Mars Hall

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Source

Answer 1

Well, you may get a stack overflow!

When you call a new function, some information about it is saved in memory. While it runs, its local variables are saved there as well. This structure is called a “stack frame”. When you call a function within a function, the stack frames that describe the caller stay there since control must (or at least is expected to) return to the caller at some point (there are techniques like tail-call optimisation to prevent that, but they don’t apply to most cases), so the deeper you go into recursion, the more stack frames are pushed onto the stack.

It may happen that you’ll run out of memory solely because of the excessive amount of stack frames on the stack, which is known as a stack overflow, which causes your program to crash.

As an example, I once wrote a recursive function that kept crashing my Python interpreter because it was running in an environment which was very low on memory. Once I removed one single local variable from said function, it stopped crashing. As you can see, sometimes one local variable (that’s copied over and over again in new stack frames) can make a difference.

Answered By: ForceBru

Answer 2

I’m curious about this myself.

Generally I’m sure I was always taught that you shouldn’t call a function from within another function, and you should instead call them one at a time and pass the return value to the next function via an intermediary variable, to avoid ‘spaghetti code’. Might take a few more lines but makes it more ‘logical’ and easy to read.

However I’m doing the Python Essentials 1 course and calling functions from within functions is part of the model answer, which was something of a surprise.

Hopefully another contributor can shed some light on this 🙂

Answered By: user1047228

What issues can arise when you call a function within a function?

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