I am having trouble understanding the flow of programming

Question

I am new to programming and one of the problems I have run across is structuring. I am learning Python (3) and am practicing by making a few practical programs. An issue I am running in to is how to get the right flow to the program. I find that as I write a function, I realize that I need it to lead to another function, so I end up calling the next function at the end of the function I'm writing. Then I realize that Python will read the code line-by-line, so I have to have the function I will be calling above the one I am actively writing. The effect is that I end up writing the program in reverse. For example:

#Replaces letters in chosen word with X's
def display_word():
 selected_word = list(selected_word)
 for x in selected_word:
 x = "X"
 print (x)
#Function that will display the welcome message when program launches
def start_screen():
 user_input = input("Hello and welcome to Hang Man! If you would like to 
start a game, please enter 'YES' now!")
 user_input = user_input.upper()
 if user_input == "YES":
 display_word()
 else:
 print ("You're no fun!")
start_screen()

This is a little tid-bit that I have written in a hang-man program I am practicing with. I started out writing the start_screen function, then realized that I will need to call the display_word function within the start_screen function, but to do that, I will have to define the function before it is called, so I have to write the display_word function above the start_screen function, which effectively has me moving in reverse. My question is whether this is the way things go or if there is a better way to do things. It seems like writing the code in reverse is inefficient, but I am unsure if that is just my inexperience talking.

• norok2: While writing functions in reversed order is considered good programming practice, it makes no real difference in Python, as long as when you use a name, that name is already being defined, e.g. swapping display_word() and start_screen() position does not make any difference, but it is not allowed to call start_screen() before its definition.

Answer 1

All functions in Python must be defined before they are used. That does not mean that the function has to be listed above the one it is called from.

The functions can be defined in any order. You just have to make sure the executable portions that start your program, like start_screen(), are called below where the function is defined.

In the case of your hangman program, you are perfectly safe to switch the order of the two functions.

In general, if you have all of your executable code following all of your function definitions, you are good to go to keep them in any order you choose!

Example:

This is perfectly ok. You can even switch them!

def fn1():
 print('I am function 1')
 fn2()
def fn2():
 print ('I am function 2')
fn1()

This is bad!

fn1() #not defined yet!
def fn1():
 print('I am function 1')
def fn2():
 print ('I am function 2')

This is also bad!

def fn1():
 print('I am function 1')
 fn2() #not defined yet!
fn1()
def fn2():
 print ('I am function 2')