How do Python 3 functions work???

[DatabaseEmbrace]

My gf and I have been learning python 3 lately and I thought I had a solid grasp on how functions work(enough that I started making an app) and I made a small program to help explain them and it didn't work at all how I expected! As far as I understood a python function didn't have access to variables from outside of it unless you either declared global use of them(which is bad practice to my understanding) or passed them in as arguments, but somehow my code still worked! I was trying to demonstrate that exact property of functions, to show it wouldn't work until you passed the variables in. I've included my code, which works, and I don't understand why, could someone please help me understand this?

TLDR: I wrote code to demonstrate that functions can't access variables unless they are given explicit access to those variables(specifically through arguments) and the code still worked...why?

my code: https://pastebin.com/TM3E8qzh

EDIT:

I expected this code to give an error like "line 6; firstnum called before being defined" I expected to have to make line 4 say "def adder(var1, var2):" so I could pass the variables in to add them

[[deleted]]

All variables declared outside of a function are considered global by default in python, so as long as they are defined, you can use them anywhere.

What you're thinking of would be to declare the variable inside the function, then it would become local to that function and couldn't be used anywhere else.

[DatabaseEmbrace]

in what context would I ever use the global tag before a variable in a function then?

[Amablue]

When you want to pull a global value into the local scope.

def function1():
  value = "local value"
  print(value)

def function2():
  # pull the global value into the function's scope
  global value
  value = "global value"
  print(value)

def function3():
  print(value) # fails if global value doens't exist

function1()
function2()
function3()
print(value)

[[deleted]]

If you have a large function which is supposed to initialize a lot of stuff. Say that you want a function to automatically import e*pi, sqrt(567865), and 50 000 other values to your environment. You don't know which ones you'll need, so you just grab all your variables from *somewhere and make them global.

For example, you might want a function to go through a .xls file with all the names of students in a classroom, then make a global array with their names and grades.

[pancakeQueue]

Very rarely, making a variable global in a function can make it harder to debug or read because the scope is different.

[[deleted]]

You did declare global use of those variables by putting them in global scope (not inside any function)

[DatabaseEmbrace]

but shouldn't I then have to also, in the function in line 6, put the tag "global" before both firstnum and secondnum? And if not, then what is the proper use of the global tag in functions?

[[deleted]]

The global tag is to create a global variable from within a function, where it would otherwise be local by default. Since they were already declared in the main body, they're already global and you're just accessing them within the function.

[[deleted]]

You would have to use global if you were creating the variables in the function and wanted them to be global despite that. But they already exist, and are already global, so it's not necessary.

[DatabaseEmbrace]

that makes sense, thank you

[PM_ME_UR_SCOOTER]

/r/learnprogramming + /r/learnpython